Seismic Rehabilitation Methods for Existing Buildings [1 ed.] 0128199598, 9780128199596

Table of contents :
Cover
Copyright
Contents
About the author
Preface
one Understanding the basic concepts in seismic rehabilitation
Aims
1.1 Introduction
1.2 What is seismic rehabilitation?
1.2.1 Rehabilitation and basic concepts
1.2.1.1 Essential rehabilitation to confront decaying effect of time (life span)
1.2.1.2 Necessity of rehabilitation from perspective of accidents
1.2.1.3 Necessity of rehabilitation in terms of preserving the environment
1.2.1.4 Rehabilitation, necessity of time
1.2.1.5 Rehabilitation and prevention of postearthquake social damages and crimes
1.2.1.6 Prevention of mental disorders and stress in crisis-stricken people through rehabilitation and precrisis management
1.2.1.7 Necessity of rehabilitation from the perspective of designing buildings against earthquake
1.2.2 Retrofitting or seismic rehabilitation in civil engineering science: which term is correct?
1.2.2.1 What is seismic rehabilitation of existing buildings?
1.2.3 Regulation standards of seismic analysis over time
1.2.3.1 Performance level regulations
1.2.3.2 Prescriptive regulations
1.3 Various types of buildings and their constituent elements
1.3.1 Materials and evaluated with its criteria
1.3.2 Structural roof
1.3.2.1 Diaphragm
1.3.2.2 Different types of roof
1.3.2.2.1 Brick arched vault roof and floor form
1.3.2.2.2 Joist-block roof
1.3.2.2.3 Compound roof
1.3.2.2.4 Traditional composite roof
1.3.2.2.5 Steel metal deck roof
1.3.2.2.6 Concrete slab roof
1.3.2.2.7 Waffle slab
1.3.2.2.8 COBIAX roof
1.3.2.2.9 ROOFIX roof and floor form
1.3.2.2.10 Prestressed roof slab and floor form
1.3.3 Seismic lateral and gravity structure main systems
1.3.3.1 Load bearing wall system
1.3.3.2 Building frame system
1.3.3.3 Simple moment frame system
1.3.3.4 Combined or hybrid system
1.3.3.5 Other structural systems
1.3.4 Foundations
1.3.4.1 Types of foundations in buildings
1.3.4.1.1 Shallow foundation
1.3.4.1.1.1 Strip foundation
1.3.4.1.1.2 Pad foundation
1.3.4.1.1.3 Balanced-base foundation
1.3.4.1.1.4 Combined foundation
1.3.4.1.1.5 Extensive (MAT) foundation
1.3.4.1.1.6 Semideep foundations
1.3.4.1.1.7 Deep foundation
1.3.4.2 Types of foundations regarding the consumable materials
1.3.4.2.1 Mortar foundation
1.3.4.2.2 Stone foundation
1.3.4.2.3 Brick foundation
1.3.4.2.4 Steel foundation
1.3.4.2.5 Reinforced concrete foundation
1.3.5 Nonstructure components
1.3.6 Building types in seismic rehabilitation grouping
1.3.6.1 Buildings with masonry materials
1.3.6.2 Buildings with concrete materials
1.3.6.3 Buildings with steel materials
1.4 Main indicators and criteria for seismic rehabilitation
1.4.1 Examining and determining the general status of the building to evaluate vulnerability
1.4.1.1 Building specifications
1.4.1.2 Deterioration in materials
1.4.1.3 Defects in designing and construction problems
1.4.1.4 History of the building and future uses
1.4.1.5 Checking and determining the status of nonstructural components
1.4.2 Determining the target performance level for seismic rehabilitation
1.4.2.1 Categorizing buildings according to importance
1.4.2.2 Performance levels
1.4.2.2.1 Structural performance level of immediate occupancy: SP-1
1.4.2.2.2 Structural performance level of life safety: SP-2
1.4.2.2.3 Structural performance level of collapse occupancy: SP-3
1.4.2.3 Earthquake hazard level in seismic rehabilitation
1.4.2.3.1 Earthquake hazard analysis and designing spectrum preparation
1.4.2.3.2 Design spectrum
1.4.2.3.2.1 Standard design spectrum
1.4.2.3.2.2 Spectrum of specific site design
1.4.3 Methods of structure analysis
1.4.3.1 Linear methods
1.4.3.1.1 Linear (equivalent)static analysis
1.4.3.1.2 Linear dynamic analysis
1.4.3.1.3 Spectrum analysis method
1.4.3.1.4 Time history analysis method
1.4.3.2 Nonlinear methods
1.4.3.2.1 Nonlinear static analysis
1.4.3.2.2 Nonlinear dynamic analysis
1.5 Identification of site specifications to investigate threats during seismic rehabilitation
1.5.1 Identifying and determining the faults their distance from of the site
1.5.2 Examining the fault risk
1.5.3 Liquefaction history, high subsidence
1.5.4 Differential settlement
1.5.5 Progressive or further liquefaction of soil
1.5.6 Liquescence (boiling smooth sand) phenomenon
1.5.7 Slipping phenomenon and slip types of mountain range
1.5.8 Draught water forces
1.5.9 Lateral spread and sequential fracture
1.5.10 Talus slope slippage
1.5.11 Landslide
1.5.12 Determining the type of land and underground water surface
References
Chapter at the glance
two Seismic rehabilitation steps and practical methods in seismic rehabilitation of existing buildings
Aims
2.1 Seismic rehabilitation studies with applied approach
2.1.1 Product and documentation of seismic rehabilitation studies
2.1.1.1 Collecting preliminary information in visiting the building
2.1.1.2 Preparation of qualitative evaluation
2.1.1.3 Experiments and digging
2.1.1.4 Report of quantities evaluation
2.1.1.4.1 Quantitative evaluation of the building
2.1.1.5 Report providing on three-method for seismic rehabilitation of existing building
2.1.1.6 Report on providing a detailed seismic rehabilitation method for top method
2.1.2 Introducing seismic rehabilitation regulation and its scope for this book
2.2 How to determine the strength of materials available in existing buildings
2.2.1 Visual assessment of the quality of materials
2.2.1.1 Pathology in concrete materials
2.2.1.1.1 Ingress of salts
2.2.1.1.2 Designing errors
2.2.1.1.3 Construction errors
2.2.1.1.4 Fire
2.2.1.1.5 Chloride attacks
2.2.1.1.6 Sulfate attacks
2.2.1.1.7 Frost action
2.2.1.1.8 De-icing salts
2.2.1.1.9 Carbonation
2.2.1.1.10 Alkali-aggregate reaction
2.2.1.1.11 Separation of concrete particles
2.2.1.1.12 Bleeding
2.2.1.2 Pathology in steel materials
2.2.1.2.1 Corrosion
2.2.1.2.1.1 Corrosion of steel outside building structure
2.2.1.2.1.2 Corrosion of inner-structure steel in a building
2.2.1.2.1.3 Corrosion of steel inside concrete and masonry materials
2.2.1.2.1.4 Metal corrosion in facilities of building
2.2.1.2.1.5 Corrosion steel buried in soil
2.2.1.2.2 Fire in steel construction
2.2.1.2.3 Designing error in steel structure
2.2.1.3 Pathology in traditional masonry materials
2.2.2 Quantity evaluation with experiments and digging results
2.2.2.1 Destruction and digging
2.2.2.1.1 Digging building components
2.2.2.1.2 Digging foundation
2.2.2.1.3 Digging columns and vertical tie
2.2.2.1.4 Digging beams
2.2.2.1.5 Digging connections
2.2.2.1.6 Digging roof in diaphragm
2.2.2.1.7 Digging masonry material component
2.2.2.2 Experiments and identification of the existing building components
2.2.2.2.1 Methods of experimenting
2.2.2.2.1.1 What is destructive methods?
2.2.2.2.1.2 What is nondestructive methods?
2.2.2.2.2 Experiments of material
2.2.2.2.2.1 Determining the mechanical specification of materials
2.2.2.2.2.2 Material strength experiments
2.2.2.2.2.2.1 Evaluation of concrete strength
Destructive experimenting methods
Compression experiment on concrete cores
Pull out experiment
Pull off experiment
Indirect tensile strength experiment (Brazilian test)
Bending experiment to calculate tensile strength of concrete
Nondestructive experimenting methods
Rebound (Schmidt) hammer
Ultrasonic pulse velocity
2.2.2.2.2.2.2 Evaluation of steel strength
Some destructive tests for steel material
Bending test
Tension test
Charpy impact test
Stiffness measurement
Rockwell stiffness
Brinell stiffness
Vickers stiffness
Nondestructive testing (NDT) for steel material
Common nondestructive testing methods
Nondestructive testing steps
Acoustic emission test
Ophthalmic exam
Radiographic examination
Magnetic particle test
Ultrasound test
Penetrant testing
Electromagnetic test
Thermography test
2.2.2.2.2.2.3 Destructive tests on masonry materials
Mortar quality control in brick infill wall with destructive experimenting
Brick compressive strength test
2.2.2.2.2.2.4 Experiments needed to determine site specifications
2.2.2.2.3 How can engineer define the required number of experiments?
2.2.2.2.3.1 Minimum level of information
2.2.2.2.3.2 Usual level of Information
2.2.2.2.3.3 Comprehensive level of information
2.2.2.2.4 Preparing digging plans and agenda
2.2.2.2.5 An example of agenda for experiments and digging, tips on digging and coring operations with algorithms
2.2.2.2.5.1 Stages of digging, sampling
2.2.2.2.5.2 Steps to sample the existing reinforcement
2.2.2.2.5.3 Steps to filling digging place with concrete masses
2.2.2.2.5.4 Surface restoration cases (positions for removing reinforcement)
2.2.2.2.5.5 Steel joist or section with I shape profile
2.3 Methods of determining the vulnerability of existing buildings
2.3.1 Rapid qualitative assessment of vulnerability
2.3.1.1 Rapid qualification of vulnerability
2.3.2 Comprehensive and detailed vulnerability assessment
2.3.2.1 Introducing effective parameters and operations
2.3.2.1.1 Stiffness
2.3.2.1.1.1 Stiffness in linear method
2.3.2.1.1.2 Stiffness in nonlinear method
2.3.2.1.2 Ductility
2.3.2.1.2.1 Structural component’s action control
2.3.2.1.2.1.1 A: Controlled by deformation
2.3.2.1.2.1.2 B: Controlled by force
Components with a brittle or nonductile behavior
2.3.2.1.3 Strength
2.3.2.1.3.1 Strength of the material in components
2.3.2.1.3.2 Capacity of structural components
2.3.2.1.4 Knowledge factor
2.3.2.1.5 Demand modifier factor (m) based on nonlinear behavior or performance level
2.3.2.1.6 Load distribution
2.3.2.1.6.1 Load combinations for linear analysis
2.3.2.1.6.2 Load combinations for nonlinear static analysis
2.3.2.1.7 Acceptance criteria for structural components capacity
2.3.2.1.7.1 Acceptance criteria for linear methods
2.3.2.1.7.2 Acceptance criteria for nonlinear methods
2.3.2.1.8 Controlling overturning effects
2.3.2.1.8.1 Overturning criteria in nonlinear methods
2.3.2.1.9 Soil and structure interaction
2.3.2.1.9.1 Analyzing interaction of soil and structure
2.3.2.1.10 Simultaneous impact of earthquake in orthogonal direction
2.3.2.1.11 Effect of vertical component of earthquake
2.3.2.1.12 Introducing the effects of P–delta
2.3.2.2 Introduction to analysis methods
2.3.2.2.1 Introduction of linear analysis methods
2.3.2.2.1.1 Linear static analysis
2.3.2.2.1.1.1 Basic assumptions
2.3.2.2.1.1.2 Major and unessential components
2.3.2.2.1.1.3 Ratio of application for linear static analysis method
2.3.2.2.1.1.4 How to determine the main fundamental period of structural oscillation
Elastic fundamental period Ti
Effective fundamental period Te
Spectral acceleration Sa
2.3.2.2.1.1.5 How to determine seismic lateral load (V) for linear static analysis
Coefficient of relate expected maximum inelastic displacements, C1
Coefficient of the effect of reducing the stiffness and strength C2
Coefficient of P–Δ effect, C3
2.3.2.2.1.1.6 Seismic force in vertical distribution method
2.3.2.2.1.1.7 Torsion
Real torsion
Accidental torsion
2.3.2.2.1.2 Linear dynamic analysis
2.3.2.2.1.2.1 Introduction to types of linear dynamic analysis method
2.3.2.2.1.2.2 The effect of concurrency of earthquake component in linear dynamic analysis
2.3.2.2.1.2.3 Application of linear dynamic analysis method
2.3.2.2.2 Nonlinear analysis
2.3.2.2.2.1 Nonlinear static analysis
2.3.2.2.2.1.1 Basic assumptions
Modeling assumptions
Target displacement
Specify target displacement
Coefficient for relation between SDOF and MDOF system, C0
Coefficient for displacement in C1
Coefficient of decrease in hardness and strength due to nonearth behavior, C2
Coefficient of P–Δ effects, C3
2.3.2.2.2.2 Nonlinear dynamic analysis
2.3.2.2.2.2.1 Basic assumptions
2.3.2.2.2.3 Modeling components in software
2.3.2.3 Chords and collectors in diaphragm
2.3.2.3.1 Chord components
2.3.2.3.2 Distributer element
2.3.2.3.3 Diaphragm analysis
2.3.2.3.4 Ceiling diaphragm design criteria
2.3.2.3.5 Diaphragm ties
2.3.2.4 Structure wall and infill panels
2.3.2.4.1 Walls
2.3.2.4.2 Structural wall
2.3.2.4.3 Infill walls
2.3.2.4.4 Separating wall (separators)
2.3.2.4.4.1 Analyzing behavior of infill frames
2.3.2.4.5 Out-of-plane strength
2.3.2.4.5.1 Force on wall post
2.3.2.4.5.2 Force on the wall
2.3.2.4.6 Integration of building parts
2.3.2.4.6.1 Two parts of building
2.3.2.4.6.2 Attachment to the adjoining components such as the parapet wall
2.3.2.4.6.3 Building separation in seismic rehabilitation
2.3.2.5 Earthquake vertical effects
2.4 Methodology for developing seismic rehabilitation strategies
2.4.1 Philosophy of seismic rehabilitation in compilation of metallurgy
2.4.1.1 A proper look at the damage to choose the type of seismic rehabilitation
2.4.1.2 Prescriptive rehabilitation
2.4.1.3 Centralized rehabilitation
2.4.1.4 Distributed rehabilitation
2.4.2 Evaluating the economic value for seismic rehabilitation for existing buildings
2.4.3 Intervention in architecture
2.4.3.1 Hidden intervention
2.4.3.2 Obvious intervention
2.4.4 Performance pattern in seismic rehabilitation targets
References
Further reading
Chapter at the glance
three Types of existing buildings: detailed introduction and seismic rehabilitation
Aims
Subchapter 3.1 Masonry structure buildings
3.1.1 Introducing types of masonry buildings
3.1.1.1 Scope of implementing the content presented in this section
3.1.1.1.1 Traditional masonry buildings
3.1.1.1.2 Modern masonry buildings
3.1.2 Understanding potential structural damage
3.1.2.1 Damages related to structural walls
3.1.2.2 Damages related to material quality
3.1.2.3 Damages related to integrity of components
3.1.2.4 Damages related to roof structures
3.1.2.5 Weakness in foundation as the common element of structure and soil
3.1.2.6 Weakness in noninstrumental walls and infill (partition)
3.1.3 Rapid vulnerability assessment
3.1.4 Comprehensive assessment of vulnerabilities in masonry buildings for reporting
3.1.4.1 Preparing as-built plans
3.1.4.2 Evaluation of structural components—analyzing test results
3.1.4.2.1 Material strength tests
3.1.4.2.2 Geotechnical tests
3.1.4.3 Quantitative vulnerability evaluation and analysis of structural components
3.1.4.3.1 Part 1: Calculating loads on the building
3.1.4.3.2 Part 2: Numerical vulnerability analysis
3.1.4.3.2.1 Modeling structural load-bearing walls
3.1.4.3.3 Part 3: Identification and analysis of defects in a building
3.1.4.3.3.1 Evaluation and identification of the defects in traditional masonry buildings
3.1.4.3.3.1.1 Defects of materials used in the building
3.1.4.3.3.1.2 Defects of structural system of the building
3.1.4.3.3.1.3 Defects in load-bearing walls
3.1.4.3.3.1.4 Diaphragm of ceiling (rigid or flexible)
3.1.4.3.3.1.5 Connection of structural components
3.1.4.3.3.1.6 Nonstructural elements of masonry materials
3.1.4.3.3.2 Evaluation and identification of the defects in masonry buildings with ties
3.1.4.3.4 Quality control of masonry materials units
3.1.4.3.4.1 Traditional masonry buildings
3.1.4.3.4.2 Masonry buildings with ties
3.1.4.3.5 Quality control of mortar
3.1.4.3.5.1 Masonry buildings
3.1.4.3.6 Control of load path
3.1.4.3.7 Integrity of masonry building
3.1.4.3.8 Irregularity in plan
3.1.4.3.9 Irregularity in height
3.1.4.3.10 Soft or weak story
3.1.4.3.11 Irregularities in geometry
3.1.4.3.12 Irregularities in mass
3.1.4.3.13 Inconsistency in vertical direction
3.1.4.4 Foundation
3.1.4.5 Adjacent buildings
3.1.4.6 Quantitative numerical vulnerability evaluation of load-bearing structural walls
3.1.4.6.1 Calculating basic shear force on building
3.1.4.6.2 Geotechnical test results to determine the type of soil
3.1.4.6.3 Evaluating shear capacity
3.1.4.6.3.1 Evaluating shear capacity of walls
3.1.4.6.3.1.1 Specifying the type of diaphragm rigidity
3.1.4.6.3.1.2 Evaluating contribution of shear force cause from earthquake
3.1.4.6.3.1.2.1 Walls with rigid diaphragm
3.1.4.6.3.1.2.2 Evaluation of shear capacity of walls with flexible diaphragm
3.1.4.6.3.1.3 Steps in calculating shear capacity of walls
3.1.4.6.3.1.3.1 Calculating section area (area of net mortared/grouted section of a wall or pier)
3.1.4.6.3.1.3.2 Evaluating vulnerability of shear capacity of a floor (story)
3.1.4.6.3.1.3.3 Investigation of in-plate behavior of walls and bases of masonry materials
Expected masonry shear strength capacity (Vme)
Evaluating wall strength in linear method
Expected lateral strength, QCE
Lower-bounded lateral strength QCL
Lower-bounded compression strength PCL
Evaluation of wall strength in nonlinear method
Acceptance criteria
3.1.4.7 Analysis of foundations and existing retain wall
3.1.4.8 Evaluation of other load-bearing walls specifications
3.1.4.8.1 Execution control of masonry units
3.1.4.8.1.1 Control of vertical bound of brickwork
3.1.4.8.1.2 Control of height to wall thickness ratio
3.1.4.8.1.3 Wall height control
3.1.4.8.1.4 Free wall length control
3.1.4.8.1.5 Wall density control
3.1.4.8.1.6 Controlling the openings distance from the bottom of the wall
3.1.4.8.1.7 Control of the toothing
3.1.4.8.1.8 Controlling load-bearing beams of the ceiling mounted on the wall
3.1.4.8.1.9 Pipes and chimneys inside the load-bearing wall
3.1.4.8.2 Evaluation of ceilings in masonry building
3.1.4.8.2.1 Support of length of ceiling beams
3.1.4.8.2.2 Openings in the ceiling
3.1.4.8.2.3 Ratio of ceiling for span to width
3.1.4.8.2.4 Thrust force control on floor arch
3.1.4.8.3 Connections of building components
3.1.4.8.3.1 Connections between load-bearing crossed walls
3.1.4.8.3.2 Connection between load-bearing walls and ceiling
3.1.4.8.3.3 Connection between walls and ceiling perpendicular to wall plate
3.1.4.8.3.4 Connection between nonstructural wall (partition) and load-bearing walls
3.1.4.8.4 Evaluating ties components in masonry building
3.1.4.8.4.1 Evaluating the existence of horizontal foundation ties
3.1.4.8.4.2 Quality evaluation of concrete ties materials
3.1.4.8.4.3 Evaluation of connection of ties
3.1.4.8.4.4 Evaluation of the ties system through detachment
3.1.4.8.4.5 Evaluation of ties through passing pipe
3.1.4.8.4.6 Evaluation of wall connection and ties
3.1.4.8.4.7 Ties dimension
3.1.5 Generalities for masonry infill wall in frames such as concrete or steel frame
3.1.5.1 What is a masonry infill wall?
3.1.5.2 Problems of neglecting infill effective of frames stiffness
3.1.5.3 What is the condition of wall for infill performance?
3.1.5.4 How can an infill frame create a soft story in the building’s structure?
3.1.5.5 How is the interaction between frames and infill frames formed in compound frames?
3.1.5.6 Distribution of stress in fill frame
3.1.5.7 Which bylaws are used in the scope of this book to evaluate brick walls?
3.1.5.8 What is the mechanism of action of infill frames against earthquake force in target displacement?
3.1.5.8.1 Border crack
3.1.5.8.2 Corner crushing mode
3.1.5.8.3 Sliding shear failure mode
3.1.5.8.4 The diagonal or tensile diagonal cracking mode
3.1.5.8.5 Diagonal compression failure mode
3.1.5.8.6 Shear failure in column
3.1.5.8.7 Short column break
3.1.5.9 Examine methods for analyzing of frames with brick walls
3.1.5.9.1 First step
3.1.5.9.1.1 Compressive strength of the existing masonry materials f′me
3.1.5.9.1.2 Tensile strength in bending fr
3.1.5.9.1.3 The expected shearing strength Vme
3.1.5.9.1.4 The expected elastic constant Eme
3.1.5.9.1.5 The expected shear modulus Gme
3.1.5.9.2 Analysis method
3.1.5.9.3 How to evaluate of masonry infill wall?
3.1.5.9.3.1 Evaluate of masonry infill wall
3.1.5.9.3.1.1 Frame collapse mode
3.1.5.9.3.1.2 Stiffness of masonry infill
3.1.5.9.3.1.2.1 Determining infill stiffness within the range of linear behavior of materials
Infill
Infill with opening area
3.1.5.9.3.1.2.2 Determining infill stiffness within nonlinear behavior range of materials
3.1.5.9.3.1.3 Strength of masonry infill
3.1.5.9.3.1.3.1 Sliding shear strength
3.1.5.9.3.1.3.2 Corner failure strength
3.1.5.9.3.1.3.3 Determination of interfacial strength in linear and nonlinear behavior range of materials
3.1.5.9.3.1.3.4 Acceptance criteria
Columns
Beams
Acceptance criteria for column in linear and dynamic static analysis method
Control of infill in the linear behavior
Infill control within the range of nonlinear behavior
Acceptance criteria in static and dynamic linear methods
Evaluation of masonry materials infills, perpendicular to the surface
Normal bending interaction
Stiffness
Strength
Acceptance criteria
Acceptance criteria within the linear behavior range
Acceptance criteria in nonlinear procedure
Conclusion
3.1.6 Common methods of seismic rehabilitation of masonry building
3.1.6.1 General seismic rehabilitation of existing building
3.1.6.2 Seismic rehabilitation in components in the story level
3.1.6.2.1 Correction of cracked spots
3.1.6.2.2 How to retrofitting with vertical and horizontal secondary ties
3.1.6.2.3 Procured of wall shotcrete
3.1.6.2.4 Using FRP fibers
3.1.6.2.5 Installing concrete shear wall
3.1.6.2.6 Installing steel brace with new frame
3.1.6.3 Seismic rehabilitation of components in ceiling level
3.1.6.4 Seismic rehabilitation in foundation level
3.1.7 Two real case study examples
3.1.7.1 Example of two-story reinforced masonry building with rigid and semi-rigid diaphragm
3.1.7.1.1 Introducing practical example 01 (building with brick masonry material)
3.1.7.1.2 Qualitative vulnerability evaluation
3.1.7.1.2.1 Geometric properties of the building
3.1.7.1.2.2 The ratio of height to width and length dimensions of the building
3.1.7.1.2.3 Type of roof system and building structure
3.1.7.1.2.4 Qualitative investigation of minimum shear strength
3.1.7.1.2.5 Determining the knowledge factor
3.1.7.1.2.6 Examining executive weaknesses in primary and secondary components and connections
3.1.7.1.2.7 Symmetry status of building plans (in terms of mass and hardness)
3.1.7.1.2.8 The status of the openings and their proximity to the floor diaphragm
3.1.7.1.2.9 Building’s components cohesion
3.1.7.1.2.10 Gravity and lateral load structure
3.1.7.1.2.10.1 Evaluating regularity in a plan in terms of quality
3.1.7.1.2.10.2 Evaluation of regularity in elevation in terms of quality
3.1.7.1.2.11 Evaluation of changes in the existing building plan
3.1.7.1.2.12 General specifications of the site
3.1.7.1.3 Rapid qualification of vulnerability
3.1.7.1.4 Digging and experiments
3.1.7.1.4.1 Foundation digging
3.1.7.1.4.2 Digging vertical and horizontal ties and their connections
3.1.7.1.4.3 Digging of ceilings
3.1.7.1.4.4 Masonry material sections
3.1.7.1.4.5 Required tests to determine site specifications
3.1.7.1.4.6 Evaluating the condition of members and components after digging
3.1.7.1.4.7 Digging foundation
3.1.7.1.4.8 Underground water and its fluidity background
3.1.7.1.4.9 Test results to determine maximum and minimum of strength of material
3.1.7.1.4.9.1 Mortar Shear capacity test
3.1.7.1.4.9.2 Schmidt Hammer test
3.1.7.1.4.9.3 Steel members
3.1.7.1.4.9.4 Mechanical test results
3.1.7.1.4.9.5 Mechanical specifications of layers of soil
3.1.7.1.4.9.6 Compression strength of bricks in walls
3.1.7.1.4.9.7 Determining lower-bound strength
3.1.7.1.4.9.8 Expected strength for materials
3.1.7.1.5 Evaluating the demand for buildings to rehabilitate
3.1.7.1.5.1 Modeling for analysis
3.1.7.1.5.1.1 Defining dead load and live load
3.1.7.1.5.1.2 Determining primary and secondary members in the models according the diaphragm rigidity
3.1.7.1.5.2 Controlling foundation of the building
3.1.7.1.5.3 Detecting vulnerable walls
3.1.7.1.6 Presenting seismic rehabilitation solution for the building
3.1.7.1.6.1 Providing lateral stiffness required for the whole structure
3.1.7.1.6.2 Making consistency in arch ceilings
3.1.7.1.6.3 Evaluating execution time
3.1.7.1.6.4 Evaluating execution cost
3.1.7.1.6.5 Evaluating advantages and disadvantages of seismic rehabilitation plans
3.1.7.1.6.6 Evaluating required facilities and equipment and skills of local labor to execute suggested options for rehabil...
3.1.7.1.6.7 Inconveniency for users or temporary suspension of the building usage
3.1.7.1.6.8 Evaluating demolishing volume of suggested executive options for rehabilitation
3.1.7.1.7 Conclusion
3.1.7.2 Example of one-story unreinforced historical masonry building with nonrigid diaphragm
3.1.7.2.1 Why should adobe buildings be rehabilitated?
3.1.7.2.2 Difference between restoration and rehabilitation in adobe buildings
3.1.7.2.3 The progressive damage mechanism in adobe buildings
3.1.7.2.4 Project introduction
3.1.7.2.4.1 Configure and recognize existing building specifications
3.1.7.2.4.2 Site specifications
3.1.7.2.4.3 Determine the weight of the building and its effective period
3.1.7.2.4.4 Determination of mechanical properties of materials used by experiments
3.1.7.2.4.5 Quantitative assessment of adobe load-bearing wall capacity
3.1.7.2.5 Providing a seismic rehabilitation plan
References
Further Reading
Masonry structure building seismic rehabilitation at a glance
Subchapter 3.2 Concrete structure frame buildings
3.2.1 Types of concrete structure buildings
3.2.1.1 Type one: concrete frame structures
3.2.1.1.1 Concrete moment frame
3.2.1.1.2 Concrete simple frame or concrete frame
3.2.1.1.3 Concrete frame with pin connection and precast sections
3.2.1.2 Type two: frame less structures with shear wall and rigid diaphragm
3.2.1.2.1 Shear wall
3.2.1.2.2 Concrete structure column and rigid diaphragm structure (beam less structure)
3.2.1.3 Type three: combined or dual concrete systems
3.2.1.3.1 Concrete simple frames with shear wall
3.2.1.3.2 Concrete moment frame including shear wall
3.2.2 Understanding potential structural damage
3.2.2.1 System weakness in concrete buildings
3.2.3 Rapid vulnerability assessment
3.2.4 Comprehensive assessment of vulnerabilities
3.2.4.1 Specification of materials
3.2.4.1.1 Lower-bound strength of concrete materials
3.2.4.1.2 Expected strength of concrete materials
3.2.4.2 Digging required in quantitative evaluation and modeling of building structures
3.2.4.3 Number of tests required at least based on seismic rehabilitation objectives
3.2.4.4 Quantitative evaluation of concrete buildings components
3.2.4.4.1 Concrete moment frame
3.2.4.4.1.1 Types of moment frames
3.2.4.4.1.2 Linear analysis and evaluation method for moment frame components
3.2.4.4.1.2.1 Calculation demand capacity ration (DCR) of components
3.2.4.4.1.2.2 Determining the stiffness of components
3.2.4.4.1.2.3 Determining components’ strength
3.2.4.4.1.2.3.1 Development length and splice of reinforcement
3.2.4.4.1.2.5 Connections
3.2.4.4.1.2.5.1 Place in cast
3.2.4.4.1.2.5.2 Postinstalled
3.2.4.4.1.3 Evaluate the capacity of components in moment frame of beam-column reinforced concrete
3.2.4.4.1.3.1 Evaluation of strength for beams in linear limitation
3.2.4.4.1.3.1.1 Flexural strength Mn
3.2.4.4.1.3.1.2 Shear and torsion strength Vn
3.2.4.4.1.3.2 Evaluation of strength in columns in linear analysis method
3.2.4.4.1.3.3 Evaluation of connections in linear limitation
3.2.4.4.1.3.4 The flexural strength of a slab
3.2.4.4.1.3.5 Slab-column connections strength
3.2.4.4.1.4 Acceptance criteria
3.2.4.4.1.4.1 Beam-column concrete moment frames
3.2.4.4.1.4.1.1 Beams control by flexural
3.2.4.4.1.4.1.2 Column control
3.2.4.4.1.4.1.3 Connections
3.2.4.4.1.4.2 Slab-column moment frame
3.2.4.4.1.4.3 Precast moment frame
3.2.4.4.1.5 Nonlinear analysis and evaluation method (static and dynamic) for moment frame components
3.2.4.4.1.5.1 Determination of stiffness of components
3.2.4.4.1.5.2 Determination of strength of components
3.2.4.4.1.5.2.1 Nonlinear static method
3.2.4.4.1.5.2.2 Nonlinear dynamic method
3.2.4.4.1.5.3 Acceptance criteria
3.2.4.4.1.5.3.1 Moment frame of beam-column reinforced concrete
3.2.4.4.1.5.3.1.1 Beams
3.2.4.4.1.5.3.1.2 Column
3.2.4.4.1.5.3.1.3 Connections
3.2.4.4.1.5.3.2 Slab-column moment frame
3.2.4.4.1.5.3.3 Precast moment frame
3.2.4.4.2 Concrete shear walls and concrete frame with infill
3.2.4.4.2.1 Modeling of concrete frames with reinforced infill frames
3.2.4.4.2.2 Types of reinforced concrete shear wall
3.2.4.4.2.2.1 In-place shear wall
3.2.4.4.2.2.2 Precast shear wall
3.2.4.4.2.3 Static and dynamic linear method
3.2.4.4.2.3.1 Determining stiffness of components
3.2.4.4.2.3.2 Determining strength of components
3.2.4.4.2.3.3 Nominal shear strength of shear walls
3.2.4.4.2.3.4 Acceptance criteria for components
3.2.4.4.2.4 Static and dynamic nonlinear analysis method
3.2.4.4.2.4.1 Determining stiffness of components
3.2.4.4.2.4.2 Coupling beams
3.2.4.4.2.4.3 Nonlinear dynamic method
3.2.4.4.2.4.3.1 Determining components strength
3.2.4.4.2.4.3.2 Component acceptance criteria
3.2.4.4.3 Foundation
3.2.4.4.3.1 General objectives of seismic rehabilitation of foundation
3.2.4.4.3.2 Access and height restrictions
3.2.4.4.3.3 Restrictions due to existing mechanical installations
3.2.4.4.3.4 Different types of foundations
3.2.4.4.3.4.1 Foundation condition (shallow foundation)
3.2.4.4.3.4.1.1 Structural conditions of foundation
3.2.4.4.3.4.1.2 Geotechnical conditions
3.2.4.4.3.4.1.3 Foundation strength and stiffness
3.2.4.4.3.4.1.4 Load-bearing capacity of foundations
3.2.4.4.3.4.1.5 Load-bearing capacity of site
3.2.4.4.3.4.1.6 Determining capacity by prescriptive analysis
3.2.4.4.3.4.1.7 Evaluation stiffness parameters on shallow and deep foundation for modeling
3.2.4.4.3.4.1.8 Introducing different types of foundation and foundation modeling
3.2.4.4.3.4.1.8.1 Separate modeling
3.2.4.4.3.4.1.8.2 Semiseparate modeling
3.2.4.4.3.4.1.8.3 Simultaneous complete modeling
3.2.4.4.3.4.1.8.4 Modeling of foundation and soil
3.2.4.4.3.4.1.8.5 Pile foundation
3.2.4.4.3.4.2 Drilled shaft foundation
3.2.4.4.3.4.2.1 Stiffness parameters
3.2.4.4.3.4.2.2 Capacity parameters (strength)
3.2.4.4.3.4.2.3 Accept criteria
3.2.5 Common seismic rehabilitation techniques, details of improving of concrete structures
3.2.5.1 Local seismic rehabilitation of members
3.2.5.2 Completely seismic rehabilitation structure or building
3.2.5.2.1 Methods of local strengthening
3.2.5.2.2 Structure retrofitting and rehabilitations strategy
3.2.5.2.3 How to use steel jacket?
3.2.5.2.4 How to use concrete jackets or reinforced concrete coverings?
3.2.5.2.5 The retraction or pretensioning method
3.2.5.2.6 How to install steel or concrete shear wall in concrete existing structures?
3.2.5.2.7 Using steel braces
3.2.5.2.8 Using concrete or masonry infill
3.2.5.2.9 Seismic rehabilitation of concrete ceiling using steel plates or section
3.2.5.2.10 Seismic rehabilitation of concrete ceiling using steel plates or section for preventing the slab punch
3.2.5.2.11 Increasing the shear capacity of the column using cross brace
3.2.5.2.12 Seismic rehabilitation of connections
3.2.5.2.13 Using FRP fibers
3.2.5.2.14 Adding extended moment frames
3.2.5.2.15 Using seismic isolators (base isolation) and damper
3.2.5.2.16 Methods of calculation for seismic rehabilitation of shallow foundation
3.2.5.2.17 Effective width of foundation
3.2.6 Two real case study examples
3.2.6.1 Example of three-story concrete moment frame building with semirigid diaphragm
3.2.6.1.1 Seismic rehabilitation steps for the project
3.2.6.1.1.1 Qualitative vulnerability assessment
3.2.6.1.1.1.1 Geometric specifications of the building
3.2.6.1.1.1.2 Type of ceiling and structures in existing building
3.2.6.1.1.1.3 Groundwater level and history of liquefaction
3.2.6.1.1.1.4 Identifying seismic rehabilitation objective
3.2.6.1.1.1.5 Specifying knowledge factor
3.2.6.1.1.1.6 Adjacent buildings
3.2.6.1.1.1.6.1 The building is free from four sides
3.2.6.1.1.1.7 Height to building dimensions’ ratio
3.2.6.1.1.1.8 Symmetry in building plan (in terms of mass and stiffness)
3.2.6.1.1.1.9 Protrusion and intrusion in the Plan
3.2.6.1.1.1.10 The status of the opening surfaces and their proximity to the floor diaphragm
3.2.6.1.1.1.11 Inconsistency of building
3.2.6.1.1.1.12 Gravity and lateral load-bearing system
3.2.6.1.1.2 Qualitative evaluation of regularity in the plan
3.2.6.1.1.3 Qualitative evaluation of regularity in height
3.2.6.1.1.3.1 Condition of interior walls and façade (outer) walls
3.2.6.1.1.3.2 Investigate the presence of heavy objects on large openings, cantilever and upper floors
3.2.6.1.1.3.3 Changes made to the building after initial construction
3.2.6.1.1.3.4 General specifications of site
3.2.6.1.1.3.5 Site specifications in terms of earthquake risk
3.2.6.1.1.4 Digging and tests
3.2.6.1.1.4.1 Examine the number and adequacy of project building experiments
3.2.6.1.1.4.2 Rapid qualification of vulnerability
3.2.6.1.1.4.3 Determine the building configuration based on digging and tests
3.2.6.1.1.4.3.1 Information on structural and decryption on structural members and connections
3.2.6.1.1.4.4 Determining minimum and maximum material strength regarding the test results
3.2.6.1.1.4.5 Conclusion from the specification by service and test consultant
3.2.6.1.1.4.6 Soil and foundation
3.2.6.1.1.5 Descriptive evaluation of buildings needs for rehabilitation
3.2.6.1.1.6 Selecting analysis model
3.2.6.1.1.7 Defining gravity load (dead and live load)
3.2.6.1.1.8 Determining the main structural and nonstructural components in the model and their stiffness
3.2.6.1.1.9 Foundation modeling
3.2.6.1.1.10 Basic controls of building structures
3.2.6.1.1.11 Nonlinear vulnerability assessment: determining target displacement for push over the structures
3.2.6.1.1.12 Combined gravity and lateral loading
3.2.6.1.1.13 Control of nonlinear structural analysis results
3.2.6.1.1.14 Evaluation of nonlinear structure response
3.2.6.1.1.15 Foundation evaluation and analysis
3.2.6.1.1.16 Evaluation of underlying soil compatibility with acceptance criteria for load bearing
3.2.6.1.1.17 Preparation of primary methods of seismic rehabilitation (review of strategies)
3.2.6.1.1.17.1 Improvement of structural components with poor performance against earthquake force
3.2.6.1.1.18 Fixing or reducing irregularities in the existing building
3.2.6.1.1.19 Determining the lateral stiffness required for the building
3.2.6.1.1.20 Increase the stiffness of the building by incorporating shear walls and reinforcing adjacent columns
3.2.6.1.1.21 Increasing strength by adding shear walls and covering columns adjacent to walls
3.2.6.1.1.22 Increasing the stiffness of the building by incorporating shear walls without boundary elements
3.2.6.1.1.23 Increasing the stiffness of the system by reinforcing the existing concrete framework
3.2.6.1.1.24 Comparison of foundation rehabilitation for upper methods
3.2.6.1.1.25 Nonlinear analysis for final seismic rehabilitation method
3.2.6.1.1.26 Binary force linear behavior model—structural displacement
3.2.6.1.1.27 Foundation rehabilitation
3.2.6.1.1.28 Comparing options economically, technically, and practically
3.2.6.1.1.29 Relative comparison of costs
3.2.6.2 Example of a tall 22-story concrete moment frame building with rigid diaphragm and central concrete core
3.2.6.2.1 Introduction of practical example (buildings with concrete structure)
3.2.6.2.2 Qualitative Assessment of this example
3.2.6.2.3 Process of seismic rehabilitation studies
3.2.6.2.4 Part I of seismic rehabilitation studies: history of building and future operation
3.2.6.2.5 General characteristics of floors
3.2.6.2.6 Existing building architecture specifications
3.2.6.2.7 Existing building structure specifications
3.2.6.2.8 Examining visible defects of the building
3.2.6.2.9 Determining the figure of the building
3.2.6.2.10 Introducing seismic rehabilitation objective for the building
3.2.6.2.11 Determining material specification
3.2.6.2.12 Status of technical documents
3.2.6.2.13 Determining concrete material specifications
3.2.6.2.14 Determining steel material specifications
3.2.6.2.15 Determining basic level for basic shear of applying earthquake level
3.2.6.2.16 Is it possible to use the building in the current status according to seismic rehabilitation regulations?
3.2.6.2.17 Examining the effects of P–Δ
3.2.6.2.18 Results of analyzing and evaluating the computer modeling
3.2.6.2.19 What solution is recommended to increase the number of floors in this building since a large area is needed?
3.2.6.2.20 Examining the structure weight
3.2.6.2.20.1 Balancing the structure mass beside increasing the number of floors
3.2.6.2.21 Key recommendation
3.2.6.2.22 Destructive part specification
3.2.6.2.23 Specifications for the attached structure
3.2.6.2.24 In case these floors are added to the building, is there a need to strengthen the seismic system and installing ...
3.2.6.2.25 Steel structure part of the project
3.2.6.2.25.1 Determining geometric specifications of used sections
3.2.6.2.25.2 Nonprismatic section beam for cantilever
3.2.6.2.25.3 Designing parts of the attached façade
3.2.6.2.26 Analyzing output results from computer modeling
3.2.6.2.27 Analyzing the effect of component stiffness on the structure stiffness
3.2.6.2.28 Sample analysis of vulnerability on the first floor
3.2.6.2.29 Analyzing average PMM stress of columns on floors
3.2.6.2.30 Explaining results from seismic separation analysis on hybrid system
3.2.6.2.31 Steps to seismic rehabilitation in this project
3.2.6.2.32 Diaphragm stiffness considering the 5cm slab on cement block and joist
3.2.6.2.33 Final analysis of the structure through nonlinear method by adding new shear walls
3.2.6.2.34 Modeling materials, elements, and components
3.2.6.2.34.1 Element material specifications
3.2.6.2.34.2 Effective stiffness of elements
3.2.6.2.34.3 Plastic joints of the elements
3.2.6.2.34.4 Target displacement calculation for rehabilitated structures
3.2.6.2.35 Interpretation of the result of evaluating nonlinear static analysis
3.2.6.2.36 How will the existing building relate to the new floors and new elements of the building facade?
3.2.6.2.37 Calculating the connection profile of the crucifix and concrete column
3.2.6.2.38 Calculating the number of shear-head components needed
3.2.6.2.39 Controlling the transfer of steel column shear to concrete bottom column (15th and 16th floors)
3.2.6.2.40 Designing steel cantilever for new concept changes
3.2.6.2.41 Investigation of metal jacket design for vulnerable columns
3.2.6.2.42 Comparison of two behaviors of mixed columns
3.2.6.2.43 Expected soil capacity
3.2.6.2.44 Modeling the existing foundation
3.2.6.2.45 Foundation evaluation
3.2.6.2.46 Evaluation of soil and foundation of the structure
3.2.6.2.47 Foundation structure evaluation
3.2.6.2.48 Results of the foundation analysis
3.2.6.2.49 Analysis results for soil stress
3.2.6.2.50 Investigation of foundation structure
3.2.6.2.51 Conclusions from the foundation examination
References
Further reading
Concrete structure building seismic rehabilitation at a glance
Subchapter 3.3 Steel structure frame buildings
3.3.1 Types of steel structure frame buildings
3.3.1.1 Framed structures
3.3.1.2 Shell structures
3.3.1.3 Suspension structures
3.3.1.4 Truss structures
3.3.2 Understanding potential structural damage
3.3.3 Rapid vulnerability assessment
3.3.4 Comprehensive assessment of vulnerabilities for existing building with steel structure
3.3.4.1 Determining the specifications of materials
3.3.4.1.1 The low-bound specifications of materials
3.3.4.1.2 Expected material specifications
3.3.4.2 Number of tests required at least based on seismic rehabilitation objectives
3.3.4.3 Steel moment frames
3.3.4.3.1 Fully restrained moment frame
3.3.4.3.1.1 Linear analysis method (static and dynamic)
3.3.4.3.1.1.1 Determining the stiffness of the components
3.3.4.3.1.1.2 Determining components strength
3.3.4.3.1.1.2.1 Evaluation of beams strength
3.3.4.3.1.1.2.2 Evaluation of columns strength
3.3.4.3.1.1.2.3 Evaluation of the panel zone strength
3.3.4.3.1.1.2.4 Evaluation of beam-to-column connection strength
3.3.4.3.1.1.2.5 Evaluation of column base plate strength
Evaluation of connection strength between base plate and concrete
Evaluation of the boundary strength between anchor bolt and concrete
3.3.4.3.1.1.3 Acceptance criteria
3.3.4.3.1.1.3.1 Deformation-controlled
3.3.4.3.1.1.3.2 Force-controlled
3.3.4.3.1.1.3.3 Acceptance criteria for beams
3.3.4.3.1.1.3.4 Acceptance criteria for columns
3.3.4.3.1.1.3.5 Acceptance criteria for panel zone
3.3.4.3.1.1.3.6 Connection in FR moment frame
Define condition acceptance criteria methods
Details of the continuity plate
The effects of a panel zone
Ratio span to depth of beam
Slenderness effects in acceptance criteria
Accept criteria of connection in FR moment frame
3.3.4.3.1.1.3.7 Connection between the foundation and base plate
3.3.4.3.1.2 Nonlinear (static and dynamic) analysis and evaluation method
3.3.4.3.1.2.1 Nonlinear static analysis method
3.3.4.3.1.2.1.1 Determining the stiffness of the components
3.3.4.3.1.2.1.2 Determination of strength of components
3.3.4.3.1.2.1.3 Strength evaluation tips include
3.3.4.3.1.2.2 Nonlinear dynamic method
3.3.4.3.1.2.3 Acceptance criteria
3.3.4.3.2 Partially restrained moment frame
3.3.4.3.2.1 Linear analysis method (static and dynamic)
3.3.4.3.2.1.1 Determining the stiffness of components
3.3.4.3.2.1.1.1 Connection node
3.3.4.3.2.1.2 Determination of strength of components
3.3.4.3.2.1.2.1 Components strength
3.3.4.3.2.1.2.2 Connections
Connection with top and bottom clip angle
Limit state one
Second limit state
Third limit mode
Fourth limit mode
Connection with using double split Tee-section
Limit state one
Second limit state
Third limit mode
Fourth limit mode
Connection with bolted flange plate
Limit state one
Second limit state
Third limit mode
Connections with bolted end plate connections
Limit state one
Second limit state
Composite partially restrained connections
3.3.4.3.2.1.3 Acceptance criteria
3.3.4.3.2.1.3.1 Acceptance criteria for primary members
3.3.4.3.2.1.3.2 Acceptance criteria for connections
3.3.4.3.2.2 Nonlinear (static and dynamic) analysis and evaluation method
3.3.4.3.2.2.1 Determining of stiffness of components
3.3.4.3.2.2.2 Determination of strength of components
3.3.4.3.2.2.3 Acceptance criteria
3.3.4.4 Brace frame
3.3.4.4.1 Bracing systems
3.3.4.4.1.1 Vertical bracing
3.3.4.4.1.2 Horizontal bracing
3.3.4.4.2 Linear analysis method (static and dynamic) for CBF brace
3.3.4.4.2.1 Steel concentric braced frame—CBF brace
3.3.4.4.2.1.1 Determining of stiffness of components for CBF brace frame
3.3.4.4.2.1.2 Determination of strength of CBF brace
3.3.4.4.2.1.2.1 Expected compression strength of CBF brace
3.3.4.4.2.1.2.2 Expected tensile strength for brace for CBF brace
3.3.4.4.3 Linear analysis method for eccentric braced frames (EBF) (static and dynamic)
3.3.4.4.3.1 Steel eccentric braced frames (EBF)
3.3.4.4.3.2 Determining stiffness of components for EBF brace frame
3.3.4.4.3.3 Determination of strength of components
3.3.4.4.4 Acceptance criteria for CBF brace and EBF brace
3.3.4.4.5 Nonlinear (static and dynamic) analysis and evaluation method for CBF brace
3.3.4.4.5.1 Determining stiffness of components for CBF brace
3.3.4.4.5.2 Determination of strength of components for CBF brace
3.3.4.4.5.3 Determination of stiffness of components for EBF brace
3.3.4.4.5.4 Determining the strength of components
3.3.4.4.5.5 Acceptance criteria for nonlinear procedure for CBF and EBF brace
3.3.4.5 Steel plates shear wall
3.3.4.5.1 Calculation stiffness for shear wall
3.3.4.5.2 Strength of steel shear wall
3.3.4.5.3 Acceptance criteria
3.3.5 Common seismic rehabilitation techniques
3.3.5.1 Methods for seismic rehabilitation of structural steelwork frame buildings
3.3.5.1.1 Introduce some seismic rehabilitation methods for steel sections
3.3.5.1.1.1 Seismic rehabilitation methods of column and beam
3.3.5.1.1.2 Seismic rehabilitation methods of steel connection
3.3.5.1.1.3 Damage to connection in steel structures
3.3.5.1.1.3.1 Damage to the beams
3.3.5.1.1.3.2 Damage of columns
3.3.5.1.1.3.3 Disadvantages and defects of welding
3.3.5.1.1.3.4 Damage to the shear coupling plate of beam web
3.3.5.1.1.3.5 Damage to panel zone
3.3.5.1.1.3.5.1 Connection failures
3.3.5.1.1.4 Seismic rehabilitation of connections against damage
3.3.5.1.1.4.1 Continuity Plates
3.3.5.1.1.4.2 Welding steel connections reinforcement solution
Use double upper and lower plates
Use diagonal plate-like hunched connection for retrofitting
Using vertical gusset plate in upper and lower flanges
Use side plates (species plates)
Use T-shaped cross section
3.3.5.1.1.4.3 Retrofitting of steel beams with external tension by tensile cable
3.3.5.1.1.4.4 Retrofitting solutions fully restrained moment connection with bolt or weld
3.3.5.1.1.4.5 Increase the length of the end plate and the use of a hardener in attaching the bolt connection to the end plate
3.3.5.1.1.4.6 Seismic rehabilitation of base plate
3.3.5.1.1.5 Seismic rehabilitation methods of steel skeleton building
3.3.5.1.1.5.1 Improving stiffness for building have a potential of soft story
3.3.5.1.1.5.2 Procedure of adding new braces to existing building
3.3.5.1.1.5.3 Procedure of retrofitting by adding new column to existing building
3.3.5.1.1.5.4 Procedure of retrofitting by adding new shear wall with concrete or steel material to existing building
3.3.5.1.1.5.5 Procedure of adding new infill wall to existing frame in building same as hybrid wall system
3.3.5.1.1.5.6 Executional procedure of compressive and tensile brace to cantilever
3.3.5.1.1.5.7 Executional procedure of a new beam between present columns
3.3.5.1.1.5.8 Seismic rehabilitation method using fiber-reinforced polymer composites
3.3.5.1.1.5.9 Seismic rehabilitation method using dampers
3.3.5.1.1.5.10 Building retrofit by seismic separation using base isolation units
3.3.6 Two real case study example
3.3.6.1 Example of 10-story steel special moment frame building + center brace frame with SMD rigid diaphragm
3.3.6.1.1 Introduction
3.3.6.1.2 Structural system type 1
3.3.6.1.2.1 Fully special restrained steel moment frame integrated with CBF braces
3.3.6.1.3 Structural system type 2
3.3.6.1.3.1 Partially restrained steel moment frame
3.3.6.1.4 Structural system type 3
3.3.6.1.4.1 Partially restrained steel moment frame + infill concrete shear walls around the structure
3.3.6.1.5 Ceiling structure and its function
3.3.6.1.6 Foundation structure type
3.3.6.1.7 Qualities evaluations for the existing building
3.3.6.1.7.1 Evaluating the consistency of the building
3.3.6.1.7.2 Evaluating the regularity in height of existing structure and its plan
3.3.6.1.7.3 Evaluating symmetry condition in the plan
3.3.6.1.7.4 Valuating height to the dimensions of the building
3.3.6.1.7.5 Evaluating opening areas within diaphragm
3.3.6.1.7.6 Evaluating integration and consistency in accessible areas to the floors
3.3.6.1.7.7 Evaluating the existing deterioration, decay, recession
3.3.6.1.7.8 Introducing the construction site of the current building
3.3.6.1.7.9 The question left, after the qualities evaluations, is that why this building should be seismically rehabilitated?
3.3.6.1.7.10 Agenda to do tests and digging
3.3.6.1.7.11 Evaluating quantitative vulnerability of floors
3.3.6.1.7.12 Determining building configuration
3.3.6.1.7.13 Determining expected and lower bound strength of material based on the test results
3.3.6.1.7.14 Soil and foundation
3.3.6.1.7.15 Define gravity load such as dead and live
3.3.6.1.7.16 Determining primary (main) and secondary components in the model and its stiffness
3.3.6.1.7.17 Foundation modeling
3.3.6.1.7.18 Primary controls of the building structure
3.3.6.1.7.19 Determining and calculating seismic evaluation parameters of the building vulnerability
3.3.6.1.7.20 Extract and Present Analysis Results
3.3.6.1.7.21 The following methods are recommended to solve the problems mentioned above
3.3.6.1.7.22 Analyzing seismic rehabilitation plan
3.3.6.1.7.23 Seismic rehabilitation of long cantilevers and façade components
3.3.6.1.7.24 Seismic rehabilitation by changing the stairway location
3.3.6.1.8 Example of tall building 18-story steel special moment frame building + concrete shear wall with SMD rigid diaphragms
3.3.6.1.8.1 Introduction
3.3.6.1.8.2 Step One: Building modeling for simulation
3.3.6.1.8.3 Compiling and extracting comprehensive structural information of the building structures for accurate modeling ...
3.3.6.1.8.4 Three-dimensional simulation in computer software
3.3.6.1.8.5 Additional information to evaluate qualitative vulnerability
3.3.6.1.8.6 Evaluating the situation in the building plan
3.3.6.1.8.7 Evaluation of irregularities in building height
3.3.6.1.8.8 Interpretation
3.3.6.1.8.9 Interpreting seismic rehabilitation methods in the 16—18 floors of the existing building according to the new a...
References
Further reading
Steel structure building seismic rehabilitation at a glance
four Nonstructural components: detailed introduction of its types and methods of seismic rehabilitation
Aims
4.1 Types of nonstructural components
4.1.1 The importance of damage to nonstructural components
4.2 Understanding potential damage
4.2.1 Assessing nonstructural components’ careful placement/layout
4.3 Rapid vulnerability assessment methods for nonstructural components
4.3.1 Characteristics of nonstructural components
4.3.2 Visual inspection
4.3.3 Behavior assessment to reach expected performance level and assessment
4.3.4 Determining samples for a complete and qualitative assessment
4.3.4.1 Availability of the plans
4.3.4.2 Unavailability of the plans
4.3.5 Checklist for nonstructural component hazards in earthquake
4.3.5.1 First part of checklist
4.3.5.2 Second part of checklist
4.3.5.2.1 Checklist of components of facilities
4.3.5.2.1.1 Emergency power generating equipment
4.3.5.2.2 Electrical devices
4.3.5.2.3 Fire communications and extinguish system includes all or parts of following equipment
4.3.5.2.4 Liquid gas storage used in emergency power system, heating, or culinary
4.3.5.2.4.1 Piping system in building includes the following
4.3.5.2.4.2 Elevators and escalators generally include the following
4.3.5.2.4.3 Heating and air-conditioning system generally includes the following
4.3.5.2.4.4 Minor mechanical machines
4.3.5.2.5 Checklist architectural components
4.3.5.2.5.1 Embedded partition wall
4.3.5.2.5.2 Stepped ceilings and soffit/intrados coverings
4.3.5.2.5.3 Lightings
4.3.5.2.5.4 Doors and exit paths
4.3.5.2.5.5 Windows
4.3.5.2.5.6 Accessories and permanent interior and exterior ornaments
4.3.5.2.6 Checklist furniture and interior content of building
4.3.5.2.6.1 Communication systems and emergency communication systems include the following
4.3.5.2.6.2 Office supplies and computer equipment
4.3.5.2.6.3 Document storage room
4.3.5.2.6.4 Kitchen and laundry appliance. Usually, all or some of these appliances are in these places
4.3.5.2.6.5 Hazardous materials
4.3.5.2.6.6 Furniture and interior decoration
4.4 Comprehensive assessment of vulnerabilities methods for analyzing nonstructural component
4.4.1 Steps in nonstructural components analytical procedure
4.4.2 Investigating requirements of nonstructural components rehabilitation based on the purpose of the study in building
4.4.3 Classification of nonstructural components according to their functional sensitivity
4.4.4 Defining seismic load for the evaluation of nonstructural components
4.4.4.1 Prescriptive procedure
4.4.4.2 Analytical procedure
4.4.5 Quantitative assessment of nonstructural components vulnerability
4.4.5.1 Calculating deformations
4.5 Details of acceptance criteria for nonstructural based on seismic rehabilitation objective
4.5.1 Nonstructural components that are sensitive to deformation
4.5.1.1 Brickwork of interior partitions or partitioning
4.5.1.2 Finishing the walls, exterior walls, facade
4.5.1.3 Decorative stones, wood, and interior mirrors
4.5.1.4 Staircase
4.5.1.5 Equipment conveyors
4.5.2 Nonstructural components that are sensitive to acceleration
4.5.2.1 Stepped ceiling
4.5.2.2 Shelters, sides, and chimneys
4.5.2.3 Stepped (false) floors
4.5.2.4 Thermal and cooling installations
4.5.2.5 Liquid reservoirs and water heaters
4.5.2.6 Pipes and their connections
4.5.2.7 Electrical and telecommunication equipment
4.5.2.8 Shelves
4.5.2.9 Elevator
4.6 Common methods for seismic rehabilitation and reducing danger of nonstructural components
A.1 Case study examples
A.1.1 Examples of seismic rehabilitation and the evaluation-bearing capacity of nonstructural components
A.1.2 How to develop a nonstructural component behavior algorithm in a building using clinical therapy?
References
Chapter at the glance
five Site pathology and seismic rehabilitation methods
Aims
5.1 Introduction to site effectivity in building performance levels
5.1.1 Determination of site properties
5.1.2 Impact of the site on earthquake
5.1.3 Rational behind seismic rehabilitation of the site
5.2 Understanding the potential damage of site treatment
5.2.1 Instability of downstream trenches of buildings
5.2.2 Instability of trenches under building’s foundation
5.2.3 Trench instability of access roads
5.2.4 Problems with soil foundation capacity modification under foundation
5.2.5 Soil liquefaction
5.2.6 Damages that lead to the rehabilitation of the subsoil
5.3 One method of rapid vulnerability for soil-bearing capacity
5.3.1 What is the safe bearing capacity of soil?
5.3.2 How to calculate safe soil-bearing capacity?
5.3.3 Final soil-bearing capacity
5.3.4 Procedures for testing determination of safe soil-bearing capacity by rapid in situ method
5.3.5 Weight loss method
5.3.6 Example
5.4 Comprehensive assessment of vulnerabilities for defining soil-bearing capacity
5.4.1 Methods for computer modeling of site component capacity
5.5 Seismic rehabilitation methods for soil of site
5.5.1 Know the density of the soil
5.5.2 The importance of soil compaction in the construction industry
5.5.3 Definition of site rehabilitation
5.5.4 Seismic/replacement methods of compaction rehabilitation
5.5.5 Compaction stages
5.5.6 Dynamic compaction
5.5.7 Preloading
5.5.8 Seismic rehabilitation with grouting
5.5.8.1 General methods of grouting in soil and rock
5.5.8.1.1 Permeation grouting in soil
5.5.8.1.2 Chemical grouting
5.5.8.1.3 Compaction grouting in soil
5.5.8.1.4 Fissure grouting
5.5.8.1.5 High-pressure grouting
5.5.8.1.5.1 Application of high-pressure grouting
5.5.9 Soil mixing
5.5.10 Underground walls for controlling water level (cutoff)
5.5.11 Nailing (nailing in soil)
5.5.12 Stone and soil anchoring
5.5.13 Soil shoring with piling
5.5.14 Methods of piling in soil
5.5.14.1 In situ pile
5.5.14.2 Precast piles
5.5.15 Micropiles
5.5.15.1 Applications of micropile method
5.6 Practical example of site seismic rehabilitation and identify potential damage
5.6.1 Evaluation and define rehabilitation methods trenches of urban development site
5.6.1.1 Overview of problems
5.6.1.2 Instability of downstream trenches of buildings
5.6.1.3 Instability of soil trenches under buildings
5.6.1.4 Trench instability access roads
5.6.1.5 Problems of foundation-bearing capacity modification
5.6.1.6 Stability of soil slope
5.6.1.7 Examine damage to retain walls that prevent trench displacement
5.6.1.8 Investigation of the general status of trench design in retaining walls
5.6.1.9 Introducing seismic rehabilitation methods for existing retain wall
5.6.1.10 Retrofitting with pre–post tensioned cables—anchoring
5.6.1.11 Retrofitting with construction of new restrained building
5.6.1.12 Retrofitting with existing retain wall and added new buttresses
5.6.1.13 Retrofitting by increasing wall section
5.6.1.14 Conclusion
5.6.2 Improvement of the site against the scouring and fluidization phenomena in the structures around the river
5.6.2.1 Introduction
5.6.2.2 Technical specifications of influential elements in the improvement process
5.6.2.2.1 Technical specifications of existing buildings
5.6.2.2.2 Technical characteristics of the soil structure
5.6.2.2.3 Technical characteristics of the site
5.6.2.3 Determination of mechanical properties required by tests for site soil
5.6.2.4 Evaluation of soil-bearing capacity
5.6.2.5 According to building weight (Table 5.6)
5.6.2.6 Rehabilitation method
Reference
Further Reading
Chapter at the glance
six Seismic rehabilitation: infographics
Aims
Index
Back Cover

Citation preview

Butterworth-Heinemann is an imprint of Elsevier The Boulevard, Langford Lane, Kidlington, Oxford OX5 1GB, United Kingdom 50 Hampshire Street, 5th Floor, Cambridge, MA 02139, United States Copyright © 2020 Elsevier Inc. All rights reserved. No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Details on how to seek permission, further information about the Publisher’s permissions policies and our arrangements with organizations such as the Copyright Clearance Center and the Copyright Licensing Agency, can be found at our website: www.elsevier.com/permissions. This book and the individual contributions contained in it are protected under copyright by the Publisher (other than as may be noted herein). Notices Knowledge and best practice in this field are constantly changing. As new research and experience broaden our understanding, changes in research methods, professional practices, or medical treatment may become necessary. Practitioners and researchers must always rely on their own experience and knowledge in evaluating and using any information, methods, compounds, or experiments described herein. In using such information or methods they should be mindful of their own safety and the safety of others, including parties for whom they have a professional responsibility. To the fullest extent of the law, neither the Publisher nor the authors, contributors, or editors, assume any liability for any injury and/or damage to persons or property as a matter of products liability, negligence or otherwise, or from any use or operation of any methods, products, instructions, or ideas contained in the material herein. British Library Cataloguing-in-Publication Data A catalogue record for this book is available from the British Library Library of Congress Cataloging-in-Publication Data A catalog record for this book is available from the Library of Congress ISBN: 978-0-12-819959-6 For Information on all Butterworth-Heinemann publications visit our website at https://www.elsevier.com/books-and-journals

Publisher: Matthew Deans Editorial Project Manager: Charlotte Rowley Production Project Manager: Sojan P. Pazhayattil Cover Designer: Victoria Pearson Typeset by MPS Limited, Chennai, India

Contents About the author Preface

ix xi

1. Understanding the basic concepts in seismic rehabilitation

1

1.1 1.2 1.3 1.4 1.5

Introduction What is seismic rehabilitation? Various types of buildings and their constituent elements Main indicators and criteria for seismic rehabilitation Identification of site specifications to investigate threats during seismic rehabilitation References Chapter at the glance

2. Seismic rehabilitation steps and practical methods in seismic rehabilitation of existing buildings 2.1 Seismic rehabilitation studies with applied approach 2.2 How to determine the strength of materials available in existing buildings 2.3 Methods of determining the vulnerability of existing buildings 2.4 Methodology for developing seismic rehabilitation strategies References Further reading Chapter at the glance

3. Types of existing buildings: detailed introduction and seismic rehabilitation

1 2 12 39 54 62 63

65 65 75 125 185 191 191 192

193

Masonry structure buildings 3.1.1 3.1.2 3.1.3 3.1.4

Introducing types of masonry buildings Understanding potential structural damage Rapid vulnerability assessment Comprehensive assessment of vulnerabilities in masonry buildings for reporting 3.1.5 Generalities for masonry infill wall in frames such as concrete or steel frame 3.1.6 Common methods of seismic rehabilitation of masonry building 3.1.7 Two real case study examples References

193 196 202 203 232 261 268 298 v

vi

Contents

Further Reading Masonry structure building seismic rehabilitation at a glance

299 300

Concrete structure frame buildings 3.2.1 3.2.2 3.2.3 3.2.4 3.2.5

Types of concrete structure buildings Understanding potential structural damage Rapid vulnerability assessment Comprehensive assessment of vulnerabilities Common seismic rehabilitation techniques, details of improving of concrete structures 3.2.6 Two real case study examples References Further reading Concrete structure building seismic rehabilitation at a glance

301 304 306 308 354 368 435 435 436

Steel structure frame buildings 3.3.1 3.3.2 3.3.3 3.3.4

Types of steel structure frame buildings Understanding potential structural damage Rapid vulnerability assessment Comprehensive assessment of vulnerabilities for existing building with steel structure 3.3.5 Common seismic rehabilitation techniques 3.3.6 Two real case study example References Further reading Steel structure building seismic rehabilitation at a glance

4. Nonstructural components: detailed introduction of its types and methods of seismic rehabilitation 4.1 4.2 4.3 4.4

Types of nonstructural components Understanding potential damage Rapid vulnerability assessment methods for nonstructural components Comprehensive assessment of vulnerabilities methods for analyzing nonstructural component 4.5 Details of acceptance criteria for nonstructural based on seismic rehabilitation objective 4.6 Common methods for seismic rehabilitation and reducing danger of nonstructural components A.1 Case study examples References Chapter at the glance

437 440 442 442 485 508 552 552 553

555 555 557 560 573 578 584 586 591 592

Contents

5. Site pathology and seismic rehabilitation methods 5.1 5.2 5.3 5.4

Introduction to site effectivity in building performance levels Understanding the potential damage of site treatment One method of rapid vulnerability for soil-bearing capacity Comprehensive assessment of vulnerabilities for defining soil-bearing capacity 5.5 Seismic rehabilitation methods for soil of site 5.6 Practical example of site seismic rehabilitation and identify potential damage Reference Further Reading Chapter at the glance

6. Seismic rehabilitation: infographics Index

vii

593 593 598 601 604 604 624 635 635 636

637 647

About the author Reza Mokarram Aydenlou has been approved as a professional member of the American Society of Civil Engineers (ASCE) and the Association of German Engineers (VDI). He is also as a mentor in ASCE collaborate. He has been trained as a professional seismic rehabilitation engineer by the Faculty of International Institute of Earth Quake Engineering and Society. After his 15 years stint in consulting as a professional designer in reputable companies and seismic rehabilitation engineer in famous projects such as high-rise building, bridge, and nonstructure, his keen interest in training young and interested engineers led him author several specialized books in this field. He has also collaborated with prestigious universities such as Khajeh Nasir Toosi and Sharif University of Technology, the Natural Disasters Research Institute, and the International Institute of Earth Quake Engineering and Society in carrying out rehabilitation projects. He is keen on developing seismic science and share his knowledge with disadvantaged areas. In his books, he has tried to introduce the reader to the topics in depth so that the content is kept in the reader’s mind for a long time. Affiliations and Expertise ASCE, VDI, Tehran, Iran

ix

Preface Earthquake as a natural event has so far created irreparable damages due to our inadequate understanding of its effects. This lack of recognition leads to this natural phenomenon being recognized as an unexpected event. In this regard, we can prevent damages by knowing certain parameters and taking effective measures. Even though we may not be able to accurately determine the time and place of an earthquake, we can able to prevent irreparable damages by identifying parameters such as the type and condition of the site and the history of earthquakes in a given area as well as building safe structures against possible earthquakes. Therefore the knowledge of performance upgrading for existing structures to the expected performance level against selective earthquakes can be applied, which is called structural seismic rehabilitation science. Today, the development of seismic rehabilitation as an engineering science in structural design is fully evident in the development of bylaws and their discussions. The major difficulty is to understand how concepts are applied and touching themes when faced with a retrofit project. Seismic rehabilitation of existing buildings seeks to enhance the performance levels of all the constituent elements of a building, including structural, nonstructural components, and site conditions to the expected best performance. Therefore it is important to have a deep understanding of the basic concepts and development of a project by creating a customizable and generalizable pattern in the user's mind. For us, the question may arise that whether or not we will be able to say that the same our seismic rehabilitation knowledge is increased in case we increase the technical knowledge of the design of the structure. It should be noted that although in today's engineering community it is true that designers are very talented, they are not mostly as successful as seismic rehabilitation engineers are with their knowledge of structure design. The answer is that we may have realized that creating an item such as a device, car, or a structure is much easier than improving or eliminating its disadvantages. Enhancement and providing solutions require a deep understanding and comprehensive modeling of the subject in an engineer's mind. Therefore seismic rehabilitation engineering can be regarded as an independent knowledge of structure design. A seismic rehabilitation engineer should be aware of all the issues surrounding the

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Preface

performance of an existing building. A seismic improvement engineer should be able to comprehend simulations (computer modeling) with a comprehensive understanding of the performance concepts of an existing building and ultimately increase the performance level of the existing building in a correct and practical manner. In this regard, it can be seen that engineering sciences in the field of seismic rehabilitation are undergoing changes and updates. The idea to write this book sparkled when I started working as a professional structure designer. About 15 years ago, I was given a project by an employer to seismically rehabilitate five schools after a severe earthquake in Bam. I was always very confident in the design of the structure and took strong steps. As I faced these projects, I realized that my responsibilities had become heavier, because I needed to take a deeper, more functional look at the subject. These types of projects are like a patient without any symptoms, but with a closer look and tests, they are diagnosed with a disease, then an appropriate treatment must be provided. There was no problem with the appearance and in operation of the buildings. However, I had to thoroughly review the buildings, identify the hidden problems accurately, and then use seismic rehabilitation, reinforcement, and upgrading. I had a very difficult task to do. To me, this was a fascinating subject in the field of civil engineering and led me into a new phase of my professional life. I did a lot of research, got professional training with leading professors at the International Institute of Seismology in Iran, and did extensive research and became increasingly involved in new and more sophisticated projects, including educational, medical, high-rise buildings, bridges, and structures of railways. At that time, I learned how to apply seismic rehabilitation codes effectively, how to accurately simulate structures so as to identify the correct defects in a building and, and finally, how to provide an executive solution for seismic rehabilitation. After 7 years of research and endeavor with the encouragement of my distinguished professors, I decided to share what I had learned in a threevolume book by one of Iran’s largest and most prominent engineering publications, Civil Engineering Publications, in a simple and practical way. I have always believed that early driving may be possible for everyone, but anyone can take part in a rally race where they feel their car is in their minds and the car is part of their body. I decided to write another book with a more thorough understanding of the algorithm, modeled on the mind of the reader, with the motto “Becoming a seismic rehabilitation engineer.” In this case, buildings are evaluated and act as a part of our

Preface

xiii

body in our minds. As a result, my viewpoint eventually became the book you now have in your hand: Seismic Rehabilitation Methods for Existing Buildings. In this book, I have tried to introduce the interested audience indepth to the basic applied topics that describe reputable journals such as FEMA 356 and to engineer their minds to do a new project so that they are able to draw a building in their minds before making any decision and to simulate some potential disadvantages. My goal in the first edition of this book is not to engage readers with numerical calculations and mathematical fundamentals, but to encourage readers to have a deep understanding of the origins of seismic rehabilitation in mind. I thought about it a lot and finally decided to present it to my audience in three main parts. First part: Introduction to basic concepts in seismic science deeply and precisely to the reader. Second part: Introduction to computer software simulation, pathology, and finally seismic rehabilitation types of structures: for base and soil alignment, for structural and nonstructural components, along with several practical application examples, I tried, regardless of numerical calculations, to identify and develop the way the reader deals with a project in mind. Third part: Using the right infographics to speed up remembering and reminding topics. In all parts of the book, I have wholeheartedly tried to create a modern way of using diagrams, illustrations, and themes. Finally, I hope to be able to transfer much of what I have in my mind to the reader in the first edition of my book, and try to add further new topics in subsequent editions. I have to say special thanks to my distinguished professors, Abdulreza Sarvgad Moghaddam and Behrokh Hosseini Hashemi, who have been my main motivation for writing this book. I would also like to thank my dear colleague Dr. Mehdi Davoodnabi for helping me in the evaluation of the examples in this book. Special thanks to my dear wife, Parisa Abdullah Zadeh, who has always been the most influential motivator for me and patiently supported me and is an exemplary mother to our children. I thank my mother for teaching me how to teach others what I have learned. I look forward to hearing from the respected readers for completing and editing the next edition of this book. Reza Mokarram Aydenlou

CHAPTER ONE

Understanding the basic concepts in seismic rehabilitation Aims By reading this chapter, you are introduced to: • • • • • • •

basic concepts of seismic rehabilitation; building components such as main structure, foundation, and roof types; types of performance level and earthquake hazard level; part of the seismic rehabilitation concepts you need to do a project effectively; site hazards of the project during an earthquake; seismic rehabilitation target; and history of compilation of seismic regulations.

1.1 Introduction The increasing development of civil engineering sciences and the evolution of seismic codes have led engineers to gain a deep understanding of the design of buildings against structural damage and potential hazards. Every day, we have news of earthquakes in different parts of the world, which have led to many deaths and financial losses. Therefore in many countries around the world, organizations have been trying to organize seismic rehabilitation operations prior to the earthquake. In the meantime, construction engineers in the current trends are trying to access available resources to perform seismic rehabilitation operations on existing structures using common patterns. Therefore it is very important for engineers to develop a comprehensive framework to deal with seismic rehabilitation projects. A deep understanding of the seismic rehabilitation process on the one hand and how an engineer can deal with a seismic rehabilitation project can be the most influential part in guiding and completing a seismic rehabilitation project. This section attempts to introduce the reader with the most influential points by preparing a model of the mind of the reader in this chapter and Chapter 2, What Is the Seismic Rehabilitation? Introduction Practical Method for Seismic Rehabilitation Seismic Rehabilitation Methods for Existing Buildings. DOI: https://doi.org/10.1016/B978-0-12-819959-6.00001-4

© 2020 Elsevier Inc. All rights reserved.

1

2

Seismic Rehabilitation Methods for Existing Buildings

Figure 1.1 Steps in becoming a seismic rehabilitation engineer in this chapter.

of Existing Building. The pattern of presenting the topics has also been such that by preparing the reader’s mind based on fully functional examples and performing seismic rehabilitation, so finally he/she can achieve the goal of BECOME SEISMIC REHABILITATION. It is advisable for the reader to follow the content in a detailed and in-depth manner, so that they can finally make use of the content and examples of the following chapters, which are fully practical examples. By reading this chapter, the reader will be acquainted with important and influential issues that can have a profound effect on their seismic rehabilitation project process. This chapter introduces the following concepts: • What is seismic rehabilitation? • Understanding the types of buildings and their components, seismic systems, foundations, ceilings, and nonstructural components. • Understanding the main parameters of seismic rehabilitation such as building importance, seismic improvement targets, earthquake, and its hazard levels. • Understanding the major hazards of a site that has a significant impact on the decision-making process of seismic rehabilitation (Fig. 1.1).

1.2 What is seismic rehabilitation? 1.2.1 Rehabilitation and basic concepts The term “rehabilitation,” in general, points at repairing and restoring an object and in construction industry this term refers to reviving or adding exploitation capability to a building and increasing its life span. More precisely, rehabilitation is a set of measures and operations that creates ability

Understanding the basic concepts in seismic rehabilitation

3

of doing a task or duties to a building which in current state, is not able to fully perform. One of the unexpected threats that affect life span expectancy of a building is earthquakes. Humans are not currently capable of preventing earthquakes; however, it is possible to prevent financial and life losses and catastrophes as well as long-term damages because of earthquakes through applying a series of methods. Renovation, repair, and reinforcement of buildings and their structures have developed, changed, evolved, and grown along with construction technique to satisfy humans’ fundamental need, that is, feeling safety. To better understand the concepts, we will look at different aspects of refinement, then the need for refurbishment will be discussed and ultimately we will come up with a comprehensive definition of seismic rehabilitation. To achieve safety in each building, first, by the help of engineering science and principles, attempts are made to provide an extent of optimal safety function and sustainability with the least amount of time and expenses. Whenever the target indices decrease from the level that is necessary for a construct to perform duties, due to any of the reasons below, the building status should be improved and enhanced to a level higher than duty level through restoration, repair, and strengthening. The reasons include: • designing building according to old and expired regulations; • inappropriate evaluation of loads; • inappropriate quality of used materials or inappropriate execution; • the effect of environmental factors or wearing out and decrease in quality of materials; and • unexpected factors such as change in building usage, restoration, and installing equipment with unpredicted loads (Fig. 1.2). In fact, for any building, there is a safety margin (distance between tensions related to duty level and design limit) considered before designing and calculations. The quality of execution plays a determining role in the safety margin and makes it provisional. In other words, before the building is constructed and when only the mathematical model and materials are considered, if consumable materials with appropriate characteristics and correct execution methods are applied, the target width will be provided and maintained for safety margin. Conversely, if materials are not of appropriate quality and execution is not correct, the width of safety margin will be less than the considered level and will decrease in time. Even if, regardless of the execution quality, we consider safety margin fixed and define a threshold for the least safety possible. This safety margin becomes

4

Seismic Rehabilitation Methods for Existing Buildings

Figure 1.2 Displays the level of duty, the requirements, and the effect of repair and reinforcement.

Figure 1.3 Safety margin diagram in technical useful life span.

narrower because of gradual material and building components wearing out, and eventually, by the end of useful life of the building, the safety margin reaches its least level. Fig. 1.3, designed according to useful technical life of the building and margin, shows the principles in algorithms from the design limit to safety margin. To prevent early dysfunctions and failures, maintenance measurements are often taken into consideration. However, when dysfunctions occur, depending on the width and importance of dysfunctions and failures, and their severity and weaknesses, measurements of repairing, improving, and strengthening should be taken. Moreover, if the dysfunctions are more severe than a predetermined limit, restoration of the whole or part of the building will be essential. Today in developing countries, construction is a high priority. This industry is under significantly fast development.

Understanding the basic concepts in seismic rehabilitation

5

However, factors such as lack of competent authorities, weakness in understanding the basic issues of the construction techniques, lack or defect of principles related to criteria and regulations of construction, noncompliance with existing principles, criteria, and regulations, weaknesses in workers’ skills and technicians, and weaknesses in work quality all cause the buildings to be worn out shortly after their completed, and therefore, repairing failures and dysfunctions will be necessary. There are a number of parameters that affect the importance of seismic rehabilitation. These parameters are discussed in the following sections. 1.2.1.1 Essential rehabilitation to confront decaying effect of time (life span) Useful life of buildings depends on different factors such as the design quality, construction quality (which by itself depends on material quality and their application), the quality of facing environmental conditions, exploitation quality, and finally maintenance quality. Although it is possible to delay erosion and prolong life span of the building through good construction, appropriate exploitation, and maintenance, there is no solution for the effects of aging and erosion. Considering what was mentioned above, every building should have the least features to be used. In designing, a level of task is considered for buildings that ensure the least features and capabilities. In addition, for a building to remain useable during time and not to lose its capabilities because of a small failure, designing is done at a higher level that is called performance level. The distance between task level and performance level is called safety margin. Over time, the characteristics of the building are reduced and the safety margin becomes narrower, and when these features reach the level of the task and fall, the life of the building ends and the building cannot be used like the first time. 1.2.1.2 Necessity of rehabilitation from perspective of accidents The probability of depletion in building capabilities should not be neglected. There are times that a building loses its desirable quality due to flood, fire, etc., and its safety margin decreases, and even a building will be unusable consequently. 1.2.1.3 Necessity of rehabilitation in terms of preserving the environment Nowadays, rehabilitation is considered a necessity in terms of the environment preservation since the waste from building demolition and using

6

Seismic Rehabilitation Methods for Existing Buildings

materials from the earth to reconstruct the demolished building hurts the environment. Rehabilitation is able to decrease the waste and the amount of materials needed for restoring and renewing a building, consequently help preserving the environment. 1.2.1.4 Rehabilitation, necessity of time We know that there is daily increase in the number and life span of buildings (including bridges and all infrastructure facilities) which are economically valuable and a part of national wealth, but the facilities to replace them are not increased relatively. Considering this fact, some people believe that decreasing the speed of population growth, especially in developed countries, can lead to the decrease in construction and increase in rehabilitating existing buildings and structures. 1.2.1.5 Rehabilitation and prevention of postearthquake social damages and crimes Careful examination of social damages and youth crimes after an earthquake and highlighting these issues for members of a society enhances the feeling of necessity and need for rehabilitating the existing buildings. The results from different researches conducted after a number of earthquakes reveal that there is a good compliance between library information and observation with related understandings. Regarding this fact that spiritual and emotional consequences after an earthquake can influence society for a long time, seismic rehabilitation, therefore, is able to decrease social damages and youth crimes in the society significantly. 1.2.1.6 Prevention of mental disorders and stress in crisis-stricken people through rehabilitation and precrisis management Although the efforts of medical professionals in the past have succeeded in eradicating various types of diseases and saving tens of thousands of people, now there must a motif in engineering community so that by using different rehabilitation methods, a wide range of mental problems after an earthquake are prevented in addition to saving lives of people. Construction, rehabilitation, and returning to normal life are the most important needs of a society that has experienced an earthquake. However, as studies show, mental disorder and stress hinder desirably performing such activities.

Understanding the basic concepts in seismic rehabilitation

7

1.2.1.7 Necessity of rehabilitation from the perspective of designing buildings against earthquake Nowadays in designing buildings against earthquakes, it is explained that safety against earthquakes is relative, and by following rules and regulations, we cannot reach absolute safety in a way that there is no damage to any buildings and structures in earthquake. In this regard, considering the following points is important: • An earthquake with a given magnitude has different severities in different areas, and the greatest severities happen in a very limited area, near the center of the earthquake. Therefore by making distance from this point, the severity of the earthquake decreases rapidly (unlike at fault location). • The cost of immunizing buildings and their structures against earthquakes increases with higher probability of damage to buildings and structures. • Earthquake forces cannot yet be accurately estimated mathematically. • With today’s human knowledge, it is impossible to eradicate the possibility of damage to buildings from the earthquake, even at unreasonable costs. • Even if we can accurately estimate the forces of earthquakes and at the expense of huge costs reduce the damage from the earthquake, there are only a few buildings that have all the facilities, which is not consistent with the logic of social life and existing facilities.

1.2.2 Retrofitting or seismic rehabilitation in civil engineering science: which term is correct? Retrofitting in civil engineering science refers to strengthening a building against applied forces. These days, this term is often used in relation to earthquake forces. From a scientific point of view, retrofitting is not a completely correct word to reflect the concept. The reason is that the term “retrofitting” does not absolutely refer to increasing a resistance against earthquake, rather this term holds improving building components against earthquake force. Therefore the term “rehabilitation,” especially for earthquake force “seismic rehabilitation” is more accurate. 1.2.2.1 What is seismic rehabilitation of existing buildings? Seismic rehabilitation means enhancing, improving, or modifying seismic performance level of structural and nonstructural components in existing buildings to reach

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minimum desirable function according to seismic regulations to have the ability to tolerate seismic movement of earth and other threats. A question might occur to any engineer that why existing buildings that seem to have retained their endurance and stability need seismic rehabilitation? Demolition of the existing buildings and their replacement with new buildings are time-consuming and uneconomic. In addition, failures because of different natural disasters are inevitable. Moreover, earthquakes may lead to interrupt services of critical structures and buildings. Therefore improving confidence coefficient of buildings’ function is of high importance. Consequently, today engineering science is progressing in the scope of assessing plan, evaluation, and seismic rehabilitation, especially in earthquake-prone countries. Daily development of regulations helps to develop different methods and options for rehabilitating buildings, each of which has its own advantages and disadvantages. This leads to the freedom of action in providing building rehabilitation plan. It must be pointed out that choosing an appropriate method for building rehabilitation requires sufficient experience and expertise since an inappropriate seismic rehabilitation plan can result in irreparable damages. Therefore it is better for a seismic rehabilitation plan to be executed by seasoned engineers in the related field. These days, by a better understanding about seismic demands of a building structure on one hand, and the recent experiences of earthquake near urban areas and the effects on existing buildings, evaluating seismic vulnerability of existing buildings is accepted as a new knowledge in the process of improving buildings functions. In addition, several regulations have been prepared for the design of seismic reconstruction engineering and have been submitted to the civil engineering community.

1.2.3 Regulation standards of seismic analysis over time The history of developing and presenting seismic regulations are mainly divided in two parts. The first part is related to local seismic standards which are regulated according to rules, climate, and regional threats. This part also includes modern seismic regulations concerning comprehensive global experiences and researches and functions of various types of buildings in different parts of the world. For a better understanding of concepts of this history, a brief explanation on seismic regulations is provided below.

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Step one On November 1755 in Lisbon, an earthquake with 8.5–9 magnitude occurred that caused nearly 100,000 casualties. After this, the construction approach in the area changed completely to increase the expected performance of the buildings. The changes were in line with government orders and regulations locally (Fig. 1.4). Step two The Messina and Reggio earthquake, which took place in Italy on December 28, 1908, had 7.1 magnitude with a seismic focus at a depth of 8–10 km from earth’s surface. The duration of the earthquake was about 30–40 seconds. The death toll is estimated to be between 75,000 and 85,000 people (Fig. 1.5). In 1909 the government ordered the formation of a geological committee composed of two main engineering teams in Italy to study damage and reduce future earthquake casualties. After studying on buildings that

Figure 1.4 The ruins of the Carmo Convent, which was destroyed in the Lisbon earthquake.

Figure 1.5 Port of Messina after the earthquake and tsunami.

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have been able to respond to earthquakes, the committee has proposed a coefficient of seismic acceleration/gravity ratio, and ultimately to apply it for acceleration of designing and constructing new buildings. This coefficient was applied as ratio of weight force for the floor and upper floors of a building. Step three On January 1, 1923, in Kantō, Japan, an earthquake with a magnitude ranging from 7.9 to 8.2 with an earthquake focus at a depth of 23 km caused a death toll of 105,000–140,000 people. The earthquake and the earlier earthquakes caused the Japanese engineer, Toshikata Sano, to develop an appropriate way to apply earthquake force for structures (Fig. 1.6). Thus, in the late 1924, a law was introduced in the urban construction regulations of Japan that 10% of the weight of the building should be considered as a horizontal force of the earthquake in building design. The Seismic Code Approach was introduced in the United States in 1925 in Santa Barbara to be considered as a law on urban construction. Step four In 1928 UBC regulations officially published the effect of earthquake force on structures as horizontal earthquake forces, which was inspired by studies of Japanese engineers. In this code, horizontal earthquake force was applied to two categories of buildings as a coefficient of building weight including dead and live loads. In this code recommending a minimum lateral design force for earthquake resistance of V=0.075 W for buildings on foundations with allowable bearing pressures of 4000 PSF 1.95 paschal or more, and 0.10 W for all other buildings including those on pile foundations. After the earthquake of 1933, at a magnitude of 6.4

Figure 1.6 The fire clouds over Kantō, as seen from some distance away.

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Figure 1.7 Damage to the John Muir School, Pacific Avenue, Long Beach.

at a depth of 10 km from the earth surface killed 115–120 people in California in the Long Beach area, for the first time, horizontal earthquake force was considered horizontally for four construction groups including regular buildings, schools, flexible buildings, and building frames in Los Angeles. This requirement included a design lateral base shear V=0.08 W for regular use buildings, 0.10 W for school buildings, and 0.04 W for the portion of a building above a flexible story. In Mexico, in 1942, the first local building code was issued. In 1966 it was completed, and in 1976 it was used as the official design and construction law (Fig. 1.7). Codification of modern regulations By the late 1960s, in advanced countries such as the United States and Japan, and in the late 1970s, in many parts of the world (such as Turkey and China), many structures were designed and constructed, regardless of seismic design standards. Therefore, in this regard, the functional review codes were formulated with various research studies on damaged structures due to various contemporary earthquakes and various functional conditions of the existing construction and nonstructural structures. The regulations were revised after the 1994 Northridge earthquake. In time, constructional codes have focused on building design and more particularly on earthquake and its effects with a more detailed view based on experiments, previous earthquakes, and scientific researches. In this regard, the seismic designing and existing building rehabilitation regulations have been evolved based on parameter of useful life span of the building and the earthquake return period. The use of seismic rehabilitation science in engineering economics and maintaining urban structures are very tangible in these regulations. At a glance, we can say that seismic regulations are developed according to two approaches which are categorized into functional regulations and prescriptive building codes.

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1.2.3.1 Performance level regulations In these regulations, a set of guidelines, criteria, and criteria for performance evaluation and control are presented with regard to the specific purpose and expectations of each designer with the desired seismic hazard levels. For example, the American Society of Civil Engineers and the Federal Emergency Management Agency, as the two leading scientific institutions, have developed a very comprehensive set of guidelines for delivering content in a functional manner. 1.2.3.2 Prescriptive regulations All of the criteria presented therein, without any special flexibility, should be provided for the level of the earthquake hazard specified in the regulations and the purpose of the regulation. It is imperative to use functional codes to accurately assess the seismic vulnerability of existing buildings, because using regulations in the event when functional regulations are not available, regarding that the rules are limited, often leads to the evaluation and presentation of noneconomic projects. In developing countries, functional regulations are carefully written based on climate conditions, academic studies, and researches, whereas in some countries, these regulations mainly contain prescriptive rules. Therefore understanding the concepts in this book are presented in a way that the reader can have a complete understanding of seismic rehabilitation steps and use these regulations in line with regulations of his/her country to rehabilitate the existing buildings. It should not be forgotten that the seismic rehabilitation of the existing buildings requires precise seismic assessment accordance with the criteria provided in the functional regulations. Therefore the concepts in this book are presented according to functional regulations.

1.3 Various types of buildings and their constituent elements Detecting the type of building structure from the perspective of seismic engineering is considered as the most important step in the beginning of seismic rehabilitation of existing building. The correct identification of the type of building and the main and nonessential elements leads to the process of preparing the reports, experiments, routines, and procedures presented for seismic reconstruction in a

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Figure 1.8 Building components sample.

fully engineered and optimal manner. For example, some of the buildings are framed with steel or concrete elements and contain a brick wall. With regard to earthquake performance, we find that these buildings are in accordance with detail with a much lower level of performance than similar conventional buildings. This means at first glance it is assumed that the building is of a steel or concrete type, but with an engineering look we find that the elements of the seismic are on the original intermediate walls with masonry material. As a result, during the seismic evaluation, this building should be placed in the category of masonry (Fig. 1.8).

1.3.1 Materials and evaluated with its criteria Building frames are a common structural system for buildings constructed of structural steel and concrete. In building frame structures, the building’s weight is typically carried by vertical elements called columns and horizontal elements called beams. In this section, we have tried to categorize the buildings under consideration to provide comprehensive identification of existing buildings, help the reader to learn concepts of third and fourth chapters by creating a deep understanding in readers’ minds, and provide a fully engineering view in consistent with seismic rehabilitation process in readers’ minds. Building components are divided into two categories: • structural components • structural roof according to the type of diaphragm • main lateral and gravity seismic systems elements • foundation • nonstructural components

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1.3.2 Structural roof Roof in civil engineering is a horizontal member that is placed on beams and is also the common and separating point between stories. The roof has a different function depending on the type of diaphragm, taking into account the deformation during the application of the side force. This function has a direct impact on the distribution of lateral forces and the behavior of the main elements of the structure to allocate the percentage of participation in the lateral force. Therefore the correct diagnosis of the roof diaphragm is very important. Roof (ceiling) tasks: • Transferring gravity loads to gravity bearing members such as columns • Transferring lateral loads to lateral bearing members such as braces and shear wall • Deflection control • Maintaining the comfort of the residents • Fire protection Questions to ask about the type of roof? • Can any roof be selected for the structure? • Do not need to control the features of the ceiling for the load it entails? • Is any roof with regard to its seismic zone capable of providing acceptable accountability for earthquake forces? To answer the above questions, it is necessary to familiarize with the different types of systems that are resistant to the lateral load (Fig. 1.9). 1.3.2.1 Diaphragm Diaphragm is a horizontal or semihorizontal system that transfers earthquake inertia forces to vertical components or lateral vertical load systems through joint function of diaphragm components including roof, edge beams, ties, reinforced concrete slab, and roof coatings. Division of diaphragm types is based on the its relative displacement due to the lateral

Figure 1.9 Lateral force resisting systems.

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load (with the fraction of the values of the full-diaphragm function), and its maximum deformation in the plan (assuming full rigid performance). Distribution of earthquake forces between lateral load elements We know that the weight of a floor of a building is concentrated on the ceiling of that floor, so the earthquake force entered into the ceiling of the structure and the roof has the duty to divide it among the members of the vertical side barrel. You may ask yourself what is meant by “relative” in the previous sentence? In the answer, it is necessary to know that the load bearing of each perpendicular side bearing system from the earthquake, depending on the amount of rigidity of the structure’s ceiling, can be based on the stiffness ratio or the ratio of the seismic weight of the frame (the contribution of its gravity load). Is it right to assume that the ceilings are rigid? At the time of designing buildings, the control of the rigidity of the ceilings has not been much considered. In the past, engineers, without any control, consider common ceilings, such as block joints, concrete slabs, steel decks, etc. as rigid diaphragms and make calculations based on this assumption. After understanding the concept of rigidity in the ceilings and investigating the possibility of not having the rigidity of the ceiling, we are more concerned with controlling it in the calculations and finding out whether the designer’s assumption is correct in the basic assumption of the ceilings as rigid diaphragm. Determining the amount of diaphragm rhythm, as the first front that is involved with the earthquake force, is of great importance. Because after distributing the story shear force at the height of the building and determining the lateral force of the floors, the cutting of each floor is distributed among the barrier elements of that class. This lateral force distribution, which is fully dependent on the diaphragm rigidity, determines the seismic load of each element of the seismic bearing, which is essential for proper design of the vertical barrier elements. In other words, if the diaphragm of ceiling has a lot of rigidity (the ceiling is rigid), the distribution of the earthquake between the lateral elements of the load will be comparable to the stiffness of each element. If the diaphragm of ceiling does not have enough rigidity or, in other words, it is flexible, the distribution of the earthquake in each element of the lateral beam will be proportional to the effective mass of that element.

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Finally, if the diaphragm is semirigid (rigid and flexible), the earthquake distribution will be carried out in two proportions for the two above-mentioned conditions (Fig. 1.10). Diaphragm components include: • diaphragm slab • chords • collectors: collectors and distribution • connect the diaphragm parts to the vertical elements of the fasteners earthquake force loader system What is the purpose of the seismic design of the diaphragm? The objective of investigating the seismic vulnerability for diaphragms is not to examine the supply of nonelastic deformations, but to study the nonelastic response to earthquake forces, which is mainly limited to the members of the lateral load system. The most important principle in evaluating the seismic vulnerability in diaphragms is to provide the hardness and strength required to connect, transfer, and integrate all of the

Figure 1.10 Diaphragm load distribution method.

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Figure 1.11 Plan geometry diaphragm deformation.

elements against earthquake forces. Factors affecting the rigidity of diaphragms: • floor slab thickness; • the type and spacing of lateral systems (bending frame, curtain and wall bracket, etc.); • plan geometry (square, rectangles, etc.); and • openings (stairs, patios, ducts, elevators) (Fig. 1.11). • Flexible diaphragm (soft) If the relative horizontal displacement of the diaphragm is greater than twice the average of its maximum deformation in plan , then the diaphragm is considered as a flexible type [1]: ΔDiaph .2 ΔStory

(1.1)

• Rigid diaphragm If the ratio is less than 0.5, the diaphragm is rigid. ΔDiaph , 0:5 ΔStory

(1.2)

In a rigid diaphragm, the intraocular deformation equals zero; that is, the infiltration of the inside of the diaphragm is infinite and the movement of all nodes inside the class is dependent on the master joint. That is, with the displacement of the center of the diaphragm mass, the displacement of the other points will be measurable.

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• Semirigid diaphragm If the ratio is between 0.5 and 2, the diaphragm is semirigid. In the half-rigid hinges, the hardness of the membrane ceiling is obtained based on the thickness of the ceiling and other elements inside the diaphragm plate. In pseudorigid diaphragms, there is no dependence between the movement of the nodes in the diaphragm (Fig. 1.12). 0:5 ,

ΔDiaph ,2 ΔStory

(1.3)

1.3.2.2 Different types of roof 1.3.2.2.1 Brick arched vault roof and floor form

Although this kind of roof is outdated and is no longer approved by the regulations, but because there are still many buildings with arched roof in different countries, engineers and other people working in the building industry should be familiar with this type of roof and know its strengths and weaknesses for seismic rehabilitation (Fig. 1.13).

Figure 1.12 Diaphragm deformation.

Figure 1.13 Brick arched vault.

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The roof consists of metal or wooden joists, which are spaced at approximately 90 cm (35 in.) apart. The gap between the joists is filled with bricks with plaster and lime mortar. In these roofs, a bit of arc in the vertical direction is created at runtime. The arched vault roof is made easily and at a low cost. However, due to its high weight and very poor performance during the earthquake, this type of roof is not reliable. This type of roof creates a soft and flexible diaphragm. 1.3.2.2.2 Joist-block roof

This roof is one of the most common types of roof in the countries of Asia and some European and American countries. Components of the joist-block roof include joist, filler block, concrete, heat reinforcement, and enhanced shear reinforcement. Among these, the first two components, the joist and the filler block, are the unique components of this type of roof. Both the joists and filler blocks have different types that are introduced here. Different types of joist are: • concrete heel joist • steel open-web joist • prestressed joist (Fig. 1.14) Different type of filler blocks: • polystyrene block • clay block • cement block Of course, it is possible to remove the filler block and, using the mold, create a shape similar to the filler block and remove the block after the concrete has been hardened. In fact, with this method, the space normally occupied by the filler block will be empty and you can use it to transfer the facility. Generally, the diaphragm in the direction of concrete beams has a rigid performance and in a vertical position on the joists, it has a flexible (soft) function (Fig. 1.15).

Figure 1.14 Joist-block roof with removable block.

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Figure 1.15 Joist block.

Figure 1.16 Composite roof.

1.3.2.2.3 Compound roof

This type of roof is applicable for concrete and steel skeletons. Its components include stringer, shearer, concrete, and temperature reinforcement. Since there is no need for shoring to run the composite roof in some methods according to beams capacity and spam, it is possible to concrete several roofs simultaneously. Molding boards or sheets should not be opened at any time sooner than the due date. The diaphragm created by this roof has a rigid performance. The roof system is divided into two types according to the type of concrete molding: • Construction of a concrete section using temporary molding in the connection between concrete and steel, in this case, the mold does not have a bearing capacity and after the implementation is mainly removed from the structure. This type of run can be implemented in both steel and concrete structures, for example, traditional composite roofs. • Using permanent molding, in this case also the mold-bearing capacity is used to calculate, for example, steel metal deck roofs (Fig. 1.16).

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Figure 1.17 Composite roof beam.

1.3.2.2.4 Traditional composite roof

This roof is one of a kind of structural ceilings that can be used on metal skeletons, also known as compound ceilings. Based on the consumable materials used in construction, compound ceilings have side beams, studs, rebar network, and concrete slabs (Fig. 1.17). 1.3.2.2.5 Steel metal deck roof

This type of roof has been widely used in West Asia for construction in recent decades. The main reason is the high speed of its execution. The components of the roof of the deck include stringer, trapezoidal galvanized sheets, studs, concrete, and temperature reinforcement. Of course, some design engineers install a flexural reinforcement at the bottom of the roof concrete (inside the console of the steel deck sheet). In fact, the design engineer ignores the role of the steel deck as a tensile element and considers the steel deck solely as a mold. Another common reason for the steel deck’s roof is its acceptable safety during the execution and function of the steel deck as an appropriate cover at the time of the earthquake (Fig. 1.18). 1.3.2.2.6 Concrete slab roof

This type of roof was one of the most comprehensive roof systems in the years before the 1980s, due to its heavy weight and low execution speeds as well as its significantly low cost. Nevertheless, some design engineers are more likely to believe in this roof and use this type of roof in their designs. In some buildings of great importance, such as buildings located

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Figure 1.18 Steel metal deck.

Figure 1.19 Slab roof with support beam.

in power plants or large industrial centers, a concrete slab roof system is used. The components of this roof are reinforcement and concrete. The slabs are either one-way or double-sided, and the difference between these two types of slabs is in the amount and direction of their reinforcement (Fig. 1.19). The factor that distinguishes a one-way slab from a two-sided slab is the ratio of the length to width. Thus, if the ratio of the length to width of the slab is less than 2, this slab is two-sided, and in the case of width lower than 2, it is considered two-sided, and is accordingly designed. One-sided slab only in transverse direction and double-sided slab in both directions require flexural reinforcement. Slabs in concrete skeletons are executed in place. First, by forming the entire surface of roof, a temporary deck is created and then reinforcement is done and concrete is placed. The molds must remain in place at least to keep the concrete hardened, and should by no means be opened before the exact time. In metal skeletons, also prefabricated slabs are used. By carefully measuring the existing framework, the strip slabs are made at the

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Figure 1.20 Slab roof without support beam.

factory in the same sizes and then installed to the project site at the desired level. These prefabricated slabs are either prestressed or routinely made. The diaphragm created by this roof has a rigid performance. Concrete slabs are executed in two ways: • slab roof with support beam • slab roof without support beam (Fig. 1.20) 1.3.2.2.7 Waffle slab

The modern waffles roofs were introduced in 1940 as an economic solution with the ease of operation to reach the tall openings. The various economic and technical benefits of waffle roofs have dramatically increased the use of this roof system. The waffle slab roof is said to be in the so-called double T, because the cross is similar to the two English letters T side by side. The diaphragm created by this roof is rigged (Fig. 1.21). 1.3.2.2.8 COBIAX roof

Studies in the field of lightweight building and removing inert concrete have established since 1985 at the universities of Germany. It is structurally similar to the two-sided slab, which, of course, has differences. In this method, some hollow lightweight balls are placed in an arranged manner in the slab thickness so that less concrete is used to fill that part. What these hollow lightweight balls do is similar to what filler blocks (foam) do in joist-block roof. This prevents filling a space with concrete when it is not required. In form, these balls are similar to low-air soccer balls that are pressed from two sides by hand. These balls are placed in the space above and below reinforcement web. To the balls to have an organized and clear arrangement beside each other, they are placed in a steal cage in

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Figure 1.21 Waffle slab roof.

Figure 1.22 COBIAX roof.

the form of a truss, and then they are placed above and below the reinforcement web. These balls are made of recycled polyethylene or polypropylene (Fig. 1.22). Due to its high cost and time-consuming execution, COBIAX roofs have not yet been able to fit into the construction industry’s structural roofs. The diaphragm created by this roof has a rigid performance. 1.3.2.2.9 ROOFIX roof and floor form

This roof is in fact the same composite roof, in which a perforated plate is used instead of a board or sheet (used as a mold). The ROOFIX is a galvanized sheet with a thickness of 0.07–0.8 mm. The ROOFIX grid makes the new concrete very well absorbed, and due to the combination of concrete and metal, the resistance obtained will be considerable to withstand the loads on the roof. The distance between stringers can be

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Figure 1.23 ROOFIX roof system.

utmost 80 cm; in case of further distance, ROOFIX may create a sag. There are two important points about concrete placement that must be considered. First, the ratio of water and concrete must never be high. In other words, the concrete must not be loose. Second, the accumulation of concrete at a separate point must be avoided, because it may be ruptured or torn due to excessive load (Fig. 1.23). The components of this type of roof include ROOFIX, reinforcement, and concrete. The simplicity of the run method and the high speed of work are the benefits of this roof, but since ROOFIX is a durable mold, it is considered as part of the consumable material of the roof and therefore increases its cost considerably. The diaphragm created by this roof has a rigid performance. 1.3.2.2.10 Prestressed roof slab and floor form

At the beginning, concrete reinforcement was used to reinforce the concrete, and then, using prestress technology, concrete was converted into one of the most practical structural materials. The idea of prestress was introduced in the first decade of the 20th century, and various researches were carried out between 1930 and 1940 (Fig. 1.24). This method has been used since 1955 in various structural fields and has grown rapidly due to its efficient use. The practical use of prestress industry began in early 1950s. At first, the focus was on manufacturing prefabricated materials for highway bridges. In 1960s constructing bridges with wide openings in boxed manner with retraced method was discussed. In recent years, using this technique became more simple and efficient, and the materials used in this method were more optimized. Currently, a high percentage of all structures under construction around the world use prestress technology. These days, factors such as the

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Figure 1.24 Prestressed roof and floor form. From https://commons.wikimedia.org/ wiki/Main_Page.

architecture needs for wide openings, designers and investors’ need for implementing unique designs in different and irregular forms, contractors and investors need for modern techniques to reduce execution time, and finally, using strong materials have led to a decrease in materials and costs, which in turn has focused attentions on using this system in structure roofs. Today, the United States, in most developed and developing societies this system is used in areas with a high risk of earthquakes or the environments where the structure is exposed to high corrosion, such as residential and office buildings, hotels, hospitals, class parking, shopping malls, stadiums, amphitheaters, high-rise buildings, special buildings such as cultural centers and memorials, and mass-build projects. In prefabricated roof, before using the structure, an initial force is made in tensile region of concrete slab using cables and their placement on roof concrete slab so that this region is not fractured after using. For this reason, the highest loading capacity of concrete is used, and accordingly the size and dimensions are reduced (e.g., joist hangers are removed). One of the main advantages of using a prefabricated roof is that it allows the structure to run with fewer pillars than other roofs. This is very important in architectural design and parking as well as the fact that some builders will still be using this roof system, despite the high cost of prefabricated roof. The components of this roof are subject to the need for technical knowledge and are simply not possible. The diaphragm created by this roof has a rigid performance.

1.3.3 Seismic lateral and gravity structure main systems The seismic systems discussed in this book are divided into four categories and during calculation of seismic rehabilitation, the main parameters from the related regulations are considered (Fig. 1.25).

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Figure 1.25 Seismic lateral and gravity structure main.

In categorizing structural systems, the criterion is related to their computational performance rather than substances and materials. The main lateral seismic structure, based on its type, can consist of beam, column, wall, and other related elements. The earthquake force is transferred to the main lateral seismic structure by diaphragm on roof. The lateral seismic system distributes and transfers the load to the foundation regarding the structure specification. Load distribution in lateral seismic system is different based on its type. Different lateral seismic systems are discussed in the following sections. 1.3.3.1 Load bearing wall system A system is a mechanism in which the load bearing walls mainly support the vertical loads, and the resistance to lateral loads is provided by the load bearing walls that act as shearing walls. Walls consisted of light coldrolled steel frames that are inhibited by steel bands or steel covering sheets are of this type of system. Load bearing masonry construction was the most widely used form of construction for large buildings from the 1700s to the mid-1900s (Fig. 1.26). Why is load bearing wall construction not used today? Load bearing masonry construction is not used today for a number of reasons: • It does not perform very well in earthquakes. Most deaths in earthquakes around the world have occurred in load bearing masonry buildings. Earthquakes love heavy buildings, because that is where they can wreak the greatest havoc. • It is extremely labor-intensive, as it is built mainly of masonry, which is made by hand. Humans have still not developed a machine that

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Figure 1.26 Load bearing wall system. From https://commons.wikimedia.org/wiki/ Main_Page.

Figure 1.27 Building frame system.

produces masonry! This also makes for very slow construction speeds in comparison with modern methods that are far more mechanized. • It is extremely material-intensive. These buildings consume a lot of bricks and are very heavy. This means that they are not green, as all this material has to be trucked around from where it is produced to the site. 1.3.3.2 Building frame system A structural system in which vertical loads are mainly supported by structural frames and resistance against lateral forces is provided by shear walls or braced frames and infill materials (Fig. 1.27). 1.3.3.3 Simple moment frame system It is a structural system in which spatial frames tolerate vertical loads and resistance to lateral walls is provided by bending frames. Structures with complete moment frames, structures with bending frames around or in

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part of the plan and frames with simple joints in other parts of the plan are of this type of system (Fig. 1.28). 1.3.3.4 Combined or hybrid system A structural system in which vertical loads are mainly supported by construction frames. Resistance to lateral loads is provided by a series of shear walls or braced frames with a set of moment frames. The shearing share of each of the two sets is determined by the difficulty and the interaction of the two in all classes (Fig. 1.29). 1.3.3.5 Other structural systems Using structural systems, except the systems mentioned above, is possible provided that their features in relation to vertical and earthquake forces are confirmed according to valid and authentic regulations around the world (Fig. 1.30).

Figure 1.28 Simple moment frame system.

Figure 1.29 Combined or hybrid system.

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Figure 1.30 Other system.

1.3.4 Foundations The foundation is part of the building, which is responsible for the transfer of force from the columns to the earth and the surrounding area. Based on the type of building and the amount of forces involved, the texture of the layer and the type of soil and the weather conditions of the region, it is possible to select the type and dimensions of the foundation. 1.3.4.1 Types of foundations in buildings The depth, length, and width of the foundations depend on the weight of the building, the number of floors, and the type of soil in the site. Different types of foundations are: • shallow foundation • deep foundation • pier foundation • special foundation, for example, post anchor Note: Remember that the above division is based on the depth of foundation to the base width (Fig. 1.31). 1.3.4.1.1 Shallow foundation

These type of foundations are built at low depths and near the surface of the earth, and they carry the loads of the structure to the ground. Usually, the ratio of depth to the width of these foundations is smaller than 3, and they can be of made stone, concrete, or reinforced concrete. Shallow foundations are divided as follows: • strip foundation • pad foundation

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Figure 1.31 Foundation load distribution.

• balanced-base foundation • combined foundation • extensive foundation 1.3.4.1.1.1 Strip foundation These foundations consist of a continuous concrete strip designed to extend the uniform load of brick, masonry, or concrete walls, as well as several pillars in a row, on a sufficient surface of the bottom (Fig. 1.32). 1.3.4.1.1.2 Pad foundation These foundations tolerate the load on a wall or column independently and separately and transfer this load to the ground. We can use this foundation type without beam. Generally, pad foundations are divided into two categories: • flexible spread footing • rigid spread footing (Fig. 1.33) Due to the fact that buildings are usually under later force, it is necessary to connect pad foundations to each other with reinforced concrete ties called ties to prevent relative horizontal movement of pad foundations. It must be mentioned that ties never help the foundation in bearing loads, and their main task is to tie columns of foundation. 1.3.4.1.1.3 Balanced-base foundation If the building’s foundation is limited to one or two ways to another building, then the foundation of

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Figure 1.32 Strip foundation.

Figure 1.33 Pad foundation.

that part of the building adjacent to the neighboring building is used as a balanced-base foundation (Fig. 1.34). 1.3.4.1.1.4 Combined foundation These foundations bear the burden of two pillars. In cases where the pillars are so close together that individual foundations interact with each other practically, or in the case where one of the pillars is located at the edge of the land limit, a two-column foundation is used (Fig. 1.35). 1.3.4.1.1.5 Extensive (MAT) foundation Extensive (MAT) foundations form a reinforced concrete layer underneath the entire building. Extensive foundations are used for buildings that are built on condensable grounds such as very soft clay, alluvial deposits, and condensable soil. Extensive foundations are divided into three categories: integrated slabs, beam and slab foundation, and slab foundation (Fig. 1.36).

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Figure 1.34 Pad foundation with tie-beam balancing the tilting effect due to different turning moments.

Figure 1.35 Combined foundation.

Figure 1.36 Extensive foundation.

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1.3.4.1.1.6 Semideep foundations The semideep foundations are inbetween the foundations and pile-forming foundations. For the implementation of semideep foundations, a well is drilled in the ground and then filled with materials. Usually, the friction of the well wall and the semideep foundation are not taken into account. Therefore the calculation of these foundations is similar to the calculation of surface foundations. If the lateral friction of the well wall and the semideep foundation are considered, its calculation will be similar to that of the piles. 1.3.4.1.1.7 Deep foundation The most common foundation is deeppile foundation. This type refers to foundations in which the ratio of depth to the smallest horizontal dimension is not more than 10. It must be mentioned that piles take the structural loads through an intermediary structure and transfer this load to the ground. Other types of deep foundations are: • pile foundations • sheet pile foundation (Fig. 1.37) 1.3.4.2 Types of foundations regarding the consumable materials Foundations can be categorized based on the materials as follows: • mortar foundation • stone foundation • brick foundation • steel metal foundation • reinforced concrete foundation

Figure 1.37 Pile foundation.

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Figure 1.38 Foundation build with stone material. From https://commons.wikimedia. org/wiki/Main_Page.

1.3.4.2.1 Mortar foundation

This type of foundation is one of the oldest foundation types around the world, and most of the old buildings have this type of foundation. Mortar foundation is currently used for small structures or low-stories structures (Fig. 1.38). Mortar is a kind of paste made of the following items: • soil • sand • lime flour • water • boulder (if necessary or in special cases) 1.3.4.2.2 Stone foundation

This foundation is built with natural stones in areas where rock is available at affordable prices. The stones used in this type of foundation should be in good shape and be of a variety of broken stones. The boulders are not suitable since they create an unstable foundation because they are polished and circular (Fig. 1.39). The surface of stone foundations is wider than the walls on it, and this surface must be 15 cm (6 in.) wider on each side of the wall. The angle for spreading load in this foundation is 45 degrees. To construct this type of foundation, two types of mortar are used. In case there is little load, lime and mud mortar is used, and if there is high load, sand and cement mortar must be used. 1.3.4.2.3 Brick foundation

This type of foundation is used when the building is small and there is little load.

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Figure 1.39 Foundation build with stone material. From https://commons.wikimedia. org/wiki/Main_Page.

Figure 1.40 Foundation with brick material.

This foundation, also similar to heavy foundations, has a root that is 15–20 cm (6–8 in.) wider than the walls on it. For this purpose, the width of the brick foundation must be 30–40 cm (11.5–15.5 in.) wider than the walls (Fig. 1.40). This excess amount within the foundation makes it easier to place bricks inside the foundation. To save on bricks, it is better to build the foundation in stepped form. This form helps to transfer the load to the ground in 60 degrees’ angle. 1.3.4.2.4 Steel foundation

If there is a heavy load on the pillar and the compressive strength of the earth is less than the limit, sometimes for steel pillars, foundations with steel web are used. It must be noted that these days using steel foundation is not possible due to economic reasons. Instead, reinforced concrete foundation is used to replace steel foundations (Fig. 1.41).

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Figure 1.41 Foundation build with steel material.

Figure 1.42 Foundation build with reinforced concrete material.

1.3.4.2.5 Reinforced concrete foundation

Nowadays, concrete foundations are the most common, and it is considered the best type of foundation in construction (Fig. 1.42). The use of other types of foundation is almost obsolete in construction work, and they are only used in special cases. For this reason, today it is recommended that the foundation be constructed of all structures with reinforced concrete. The most important factors in choosing the type of foundation during construction and design are as follows: • climatic conditions of the area • geographic location • understanding the economic and cultural situation of the people in the region • type of soil and its strength • amount of load from the building to the ground In terms of thickness or vertical section, single foundations can be fixed, stepped, or sloped.

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1.3.5 Nonstructure components These elements do not have any effect on load bearing system in the building. However, at time of earthquake, they can affect the entire function of a building because of the function they have (Fig. 1.43). For example, stairways, facade, bulkhead, refrigeration and thermal equipment and installations, and any other linking system between floors are not seismic members of the building. In case these members and their linking function are damaged at the time of earthquake, the entire function of the building decreases significantly (Fig. 1.44).

Figure 1.43 Nonstructural components in building.

Figure 1.44 Facade damage.

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In general, for assessment approach, these elements are divided into two groups: • sensitive to acceleration • sensitive to relocation Therefore it is required to identify nonstructural elements during seismic rehabilitation studies and apply an appropriate approach to determine the expected performance and improve performance of these elements. In Chapter 5, Site Pathology and Seismic Rehabilitation Method, we will discuss nonstructural components in more detail.

1.3.6 Building types in seismic rehabilitation grouping In general, the buildings in question are divided into three main groups, considering the materials used in the construction of their main structures, regardless of the structural system. 1.3.6.1 Buildings with masonry materials The buildings in which lateral seismic structure is made of masonry material such a brick and cement blocks, etc. are of this type of buildings. Structural systems of this category are wall system and building frames introduced in “different structural systems” Section 1.3.3.1. 1.3.6.2 Buildings with concrete materials Building that have their lateral seismic system build with reinforced concrete materials are classified in this category regardless of their structural system. Structural systems of this type are concrete load bearing wall system, moment frames, hybrid systems, and other systems introduced in types of structural systems. 1.3.6.3 Buildings with steel materials Buildings in which lateral seismic structure is built with steel material such as beam, column, brace, and steel shear wall and any steel sections, regardless of their structural system, are in this category. Structural systems of this type are moment frames, hybrid systems, and other systems introduced in types of structural system.

1.4 Main indicators and criteria for seismic rehabilitation For seismic rehabilitation of the existing buildings, there are several indicators and criteria, most notably determining the goal of seismic

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reconstruction. Determining this index requires appropriate identification of the building importance, performance level of the building, and levels of danger. Therefore efficient steps for determining indices are introduced. These steps include all buildings regardless of their structural types. These steps are as follows: • examining and determining general status of the building to evaluate vulnerability • determining the target performance level for seismic rehabilitation • determining the importance of the building • determining performance levels • earthquake hazard levels • analysis of methods

1.4.1 Examining and determining the general status of the building to evaluate vulnerability All general characteristics of the building, including the number of floors, the type of roof diaphragm, the status of the neighboring buildings on the plan, regularity and irregularity in the plan, the total area of the building under study, the height of the floors, the dimensions of the building, the type of soil in the presence of basic information, type of foundation, if the map is available, the type of building system are first studied. Each of these pieces of information has a significant impact on the evaluation of the seismic rehabilitation and the objective of seismic rehabilitation of the existing buildings. 1.4.1.1 Building specifications Determining accurate dimensions of the building in terms of height, width, length, the number of floors has significant effect on understanding building importance. All specifications from observations and examining available maps must be extracted to prepare a checklist for fast evaluation of existing building vulnerability and to determine the goal for seismic rehabilitation. These are as follows: • building’s specifications and history; • geographical location and date of construction; • building’s use and performance of its parts and space; • the type materials and roof type (diaphragm); • geometric dimensions, number and height of floors, or regularity and irregularity of buildings on plan and altitude; • stair position, access to floors and escape stairs;

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• lateral and gravity load bearing system; • the state of symmetry in the building plan (in terms of mass and stiffness); • plunging and outburst situation; • the position of the opening surfaces and their proximity to the diaphragm and the degree of breakage seams; and • nonstructural components. It must be noted that in this section, no evaluation is made of the items above according to existing regulations, and eventually, rehabilitation is based on the chapters of the final report on fast evaluation. 1.4.1.2 Deterioration in materials As long as materials are not digging, we cannot certainly know about deterioration of material. However, if we witness deterioration in the structure, we can identify the existing problems according to a table specifying materials and type of the element. 1.4.1.3 Defects in designing and construction problems Before digging in report, by paying attention to construction year and observable problems, we cannot certainly understand defects of design and execution problems. Therefore, by paying attention to structure, openings’ position, plan dimensions, and other observable cases, according to regulations and principles at the time of building, we can find out about problems and defects. 1.4.1.4 History of the building and future uses This section of primary evaluation is to prepare a table with the following items to check the history of the building and its uses: • items of the design year and construction year; • determining the building design guidelines; • checking calculations and studies on the building; • supervisor’s name or project monitoring institute; • the date that construction started; • the duration of different stages of construction and the duration of operation of the building; • determining the primary utilization of the building; • determining building applications so far; • investigating potential future building changes;

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• determining of faults and repairs made in structural, nonstructural, joints, and building structures; • determining changes in plan, walls, flooring, and roof during operation; and • determining the capacity of the building (personnel). 1.4.1.5 Checking and determining the status of nonstructural components In this section, all the specifications of the building are considered according to the status and observed cases by the expert and will be used in the quick evaluation of vulnerability. The related specifications to be investigated and determined are: • the status of nonstructural components of the type; • the status of the observable cracks and their location; • the status of the walls of the separator and the walls of the facade; • the probability of the separation and collapse of members and nonstructural parts, especially the facade and glass; • prediction of mortality and financial damages; and • examining the extent of deterioration in nonstructural components including architectural, mechanical, electrical, telecommunication, medical, laboratory, industrial, and sensitive equipment, warning systems. The internal separating walls and facade wall must be observed. There must not be any cracks, breaks, or separation in facade parts.

1.4.2 Determining the target performance level for seismic rehabilitation One the most important seismic vulnerability evaluation of the existing buildings is the rehabilitation target. The result of the following processes leads to determining rehabilitation goal. • The importance of the building is determined from various considerations of use, the size and value of the building, the consequences of the damage, and the view of the user. • The desired hazard levels are determined from earthquake hazard zonation or special studies, as well as special requirements for use in the building. • The expected levels of performance are determined at each level of hazard from the two above-mentioned factors, plus the financial strength of the operator plus the special needs in the usage.

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• The criterion for measuring the expected performance is the acceptance criteria defined quantitatively and precisely. To determine rehabilitation target, it is required to accurately understand the main parameters that depend on the importance of building. These parameters are: • categorizing the importance of the building • performance levels • seismic level of hazard The important point is that the rehabilitation goal is often proposed by the user. However, in some cases, by paying attention to parameters such as the importance of the building and seismicity of the region, seismic rehabilitation experts must be able to determine and follow this parameter in their seismic rehabilitation studies of existing building. The importance of the building is determined by the use, size, and value of the building, the effects and consequences of the damage, and the view of the operator. Therefore there is a need for a systematic solution for the above grouping with technical, economic, and social case studies, which ultimately comes with the view of the exploiters and users. The most important goals of seismic reconstruction are: • To provide resistance to mild earthquakes without any damage to the elements. • To provide resistance to moderate earthquakes without any structural damage, but there is a potential for some nonstructural damages. • To provide resistance to severe earthquakes that have already occurred in a building site or can occur, without failure, but there are likely to be some structural and nonstructural damages. Target building performance levels in seismic rehabilitation Sample method for choosing a target for rehabilitation with a qualitative view • For buildings of great importance and necessary buildings: special or desirable rehabilitation. • For buildings of mediocre important and necessary buildings: basic or desirable rehabilitation. • For buildings with low importance: no rehabilitation or basic rehabilitation. • Note that in most of the current projects, the rage for rehabilitation is of higher importance than basic performance level, and for schools “basic” rehabilitation and in some cases “desirable” rehabilitation is considered.

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Figure 1.45 Seismic rehabilitation target flowchart [2,3].

The range for seismic rehabilitation, regarding the performance level, earthquake hazard level, and cost of seismic rehabilitation, are mainly placed in four categories (Fig. 1.45). • Limited seismic rehabilitation The target for seismic rehabilitation is considered for the lowest performance level so that the safety of the residents is provided in an earthquake that is weaker than the first hazard level of earthquake. • Basic rehabilitation target In this target, it is expected that the seismically rehabilitated building provides safety of the residents in an earthquake at the first hazard level. • Desirable rehabilitation target In this target, it is expected that first, basic rehabilitation target, is provided, and second, the seismically rehabilitated building provides safety of the residents in an earthquake at the second hazard level. • Specific rehabilitation target In this target, a better performance than desirable rehabilitation target, is expected. In other words, a building that is seismically rehabilitate must have a better performance than the previous target and also must have a performance in providing life safety of residents and uninterrupted usability in an earthquake at the second hazard level. • Local (positional) rehabilitation target

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In local rehabilitation, one of the four main rehabilitations is performed. The changes in this rehabilitation affect the performance of the building; however, these changes must not lead to the following items: • Changes must not result in decrease in the previous performance of the building. • Changes must not increase the forces of earthquake in members that are in critical situation. • Changes must not lead to irregularity in mass, stiffness, and plan of the building under construction. 1.4.2.1 Categorizing buildings according to importance Categorizing buildings according to importance is a very important parameter. This parameter aims to determine the expected performance for the building after seismic rehabilitation. This classification is possible by paying attention to the following features: • Identifying the features of the building in terms of: • use, including its role in solving problems at the time of crisis and earthquake, importance of rescuing, security, military, service providing, communication; • capacity of residents of building; • the importance of people present in the place; • material and spiritual value of the building; • value of the materials inside the building; • the remaining and acceptable useful life of the building; • secondary hazard of damage to facilities inside the building; and • the sensitivity of the facilities inside to seismic damage. • Classifying the building in the scale of user community (national, regional, local, and personal property scale). • Paying attention to rules and third party rights. • Paying attention to mental, political, and social consequences. Hazard levels for rehabilitation are determined by reference to earthquake hazard zone or special studies and special needs in the building in the study. Ultimately, the importance of the building, the level of hazard involved, the financial viability of the user, and the specific needs of the user can determine the expected performance levels at each level of hazard. 1.4.2.2 Performance levels To achieve the best rehabilitation plan at the time of the seismic rehabilitation of existing buildings, it is necessary to ensure that the proper

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performance levels set for the purpose of rehabilitation are provided. Therefore the underpinning of all steps related to the seismic reconstruction process should be well understood. Performance levels for the building have four main levels and two intermediate levels. The main performance levels are: • immediate occupancy • life safety • collapse prevention • not included (not specified) Intermediate performance levels include: • limited downtime • limited life safety Each of the performance levels presented above is dependent on the two main parts, level of damage and seismic hazard level. In other words, for the performance of each building during an earthquake, a level of hazard should be considered, and acceptable or expected damage should be defined accordingly. Therefore each damage level should be consistent with the hazard level. Therefore seismic performance is the minimum permissible damage (performance level) for accepting certain seismic hazard (earthquake hazards). The aim of a performance level can include different levels of damages for different levels of earth movement. Performance levels for structural and nonstructural components are considered independently. The level of performance in determining the goal of improvement is divided into two groups: • performance level of structural components, SP-n • performance level of nonstructural components, NP-n Each of these two levels can provide the overall performance independently or in combination. Structural function levels and scope are introduced with a title and a single number, called the “structural performance number,” in abbreviated form SP-n. 1.4.2.2.1 Structural performance level of immediate occupancy: SP-1

At this level of building performance, the main elements, both horizontal and vertical, which face earthquake forces, have the necessary resistance and, without damage, retain all the properties and characteristics of the preearthquake seismicity (Fig. 1.46). This level of performance is indicated on the capacity curve by the range A to B in Fig. 1.49.

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Figure 1.46 Structural performance level immediate occupancy.

Figure 1.47 Structural performance level life safety.

1.4.2.2.2 Structural performance level of life safety: SP-2

In this level, there are some damages in the structure after an earthquake, but the extent of damages is not high, thus there is no life loss. This performance is a postsituation earthquake in which considerable damage has been made in the structure, but there is no certainty margin in collapse of the whole or part of the building (Fig. 1.47). The level of failure that is considered for its collapse threshold level is low. Major members of the structure have not been dislocated or collapsed, and there is no life danger inside or outside the building. Although during the earthquake injuries may occur, the probability of serious injuries resulting to death due to structural damage is very low. This level of performance has a significant difference with total or partial collapse and is indicated on the capacity curve in Fig.1.49 around point G. 1.4.2.2.3 Structural performance level of collapse occupancy: SP-3

In this case, due to the occurrence of the earthquake, a widespread destruction occurs in the structure, but the building does not collapse and

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Figure 1.48 Structural performance level collapse occupancy.

Figure 1.49 Diagram for force and displacement target [2,3].

the mortality rate is minimal. This level of performance is the ultimate breakdown level after an earthquake, in which the whole or part of the structural system of the building is on the verge of collapse. Major damages to the structure entail a severe reduction of hardness and resistance in the lateral load system (Fig. 1.48). However, at the same time, all the main components of the system load on the verge also able to continue to bear the load. Although the building maintains its overall sustainability, the possibility of damage due to the collapse of the main structural members both inside and outside the building is extremely severe, and the possibility of a collapse of the building in the event of an aftershock is high. It should be noted that structural repairs must be carried out before resettlement in the building. In this situation, for old buildings, it is very likely that the damage caused is not

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Figure 1.50 Performance level for building, structure, and nonstructure [2,3].

economically and technically repairable at all. At this level, there is a hazard of falling components, which is why the nonstructural performance level is unacceptable for this issue. In the chart provided in Fig. 1.49, the performance levels for components of structural and nonstructural components and building according to the criteria of FEMA-356 is offering. Deformation according to force and shift shape. In Fig. 1.50, the minimum and maximum required performance levels are presented. Performance level of structural components

Performance level of nonstructural components

Building performance level

• • • • • •

• • • • •

• Operational occupancy • Immediate occupancy • Life safety • Collapse prevention

Immediate occupancy Limited downtime Life safety Limited life safety Collapse prevention Not considered

Operational occupancy Immediate occupancy Life safety Limited life safety Not considered

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1.4.2.3 Earthquake hazard level in seismic rehabilitation This means introducing earthquake force based on a parameter of probability percent of occurrence during shelf life span of the building with a determined repetition period. 1.4.2.3.1 Earthquake hazard analysis and designing spectrum preparation

For any seismic rehabilitation plan, it is necessary to determine the factors related to the earth’s strong motion on the earth surface for different levels of hazard. The methods are presented schematically in this way (Fig. 1.51). The various levels of earthquake hazard level due to the type of earth movement are defined as in the following. • Hazard level one: DBE or DE—design base earthquake This hazard level is on the surface enamel of earthquakes, with an earthquake likely to be greater than 10% over a period of 50 years; the earthquake return period is 475 years. This level of hazard is synonymous with hazard level in a prescriptive regulation. • Hazard level two: MPE—maximum probable earthquake This hazard level is defined based on 2% occurrence probability in 50 years with return period of 2475 years. • Optional hazard level This hazard level is suitable for special cases or considerations, and in fact, it can be a seismic index with probability of occurrence in 50 years. • Serviceability earthquake hazard level Serviceability earthquake is a mild or intermediate earthquake that corresponds to a level of earthquake based on probability theory. The occurrence probability of an earthquake greater than this in 50 years is 50%. The return period of this earthquake is around 72 years, which is

Figure 1.51 Evaluating parameters of earth’s strong movement on earth surface [2,3].

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introduced approximately 75 years. This earthquake level generally is half the design level earthquake. Serviceability earthquake has 99.5% probability of occurrence in 50 years. In other words, earthquake happens during the life span of the building. • Maximum earthquake hazard level—ME A maximum earthquake is defined as the maximum earthquake level expected from a geologically defined area. Extreme levels of earthquake probability represent a level of earthquakes. An earthquake greater than this level is more than 50% likely to occur in 50 years. 1.4.2.3.2 Design spectrum

After the earthquake has been selected to determine the performance purpose, its specifications should be appropriately stated. How the earthquake specifications are stated and used depends on the method that is chosen based on the performance? Usually, the expression of earthquake characteristics is done in two ways, one using the spectrum of the desired earthquake passage and the other using accelerated mapping and time history. To express the desired earthquake characteristics using the response spectrum, one can use the standard response spectrum specified in the regulations or construct a specific range of structures. 1.4.2.3.2.1 Standard design spectrum The standard design spectrum depends on two important factors: the design basis and the soil properties. The basis acceleration is achieved using seismic zoning maps, in which the maximum acceleration rates for different return periods are obtained. This is presented in the US regulations ASCE and FEMA. 1.4.2.3.2.2 Spectrum of specific site design The special site design spectrum that is based on a specific hazard analysis and for special rehabilitation depends on several important factors such as: • conditions of the site • magnitude of earthquake • distance of fault from the site • type of soil and relative reduction relation • method of hazard level evaluation For the specific hazard analysis of the site, active faults must be determined around the site up to a radius of 100 km. Seismic parameters should be determined based on earthquake databases and seismic maximum of the area. By paying attention to geotechnical, seismic, and

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seismological conditions of the site, an appropriate reduction relation must be obtained.

1.4.3 Methods of structure analysis To evaluate the capacity of structural members, we need to be familiar with the methods of analysis. Case analysis methods for seismic rehabilitation can be divided into following four main groups (Fig. 1.52). 1.4.3.1 Linear methods • Equivalent static analysis • Spectral dynamics • Time history 1.4.3.1.1 Linear (equivalent)static analysis

The basic assumptions of linear static analysis are: 1. Behavior of materials is linear. 2. Earthquake loads are static (static). 3. The total force on the structure is equal to the weight of the building. In this method, lateral force from the earthquake is chosen in a way that basic shear resulting from this force is equal to basic shear force according to regulations. The value of basic shear is chosen in such a way that structure deformation will be according to what has been predicted in the target earthquake hazard level. If the structure is behaved linearly under the influence of load, the forces obtained for structural members will be close to those predicted during the earthquake, but if the structure has a nonlinear behavior, then the calculated forces in this way exceed the values of material. For this reason, when examining accepting criteria, the results from linear analysis for structures that have nonlinear behavior are corrected.

Figure 1.52 Methods of structure analysis [2,3].

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1.4.3.1.2 Linear dynamic analysis

Linear dynamic analysis can be done in two ways: spectral or historical. The specific assumptions of this method in the linear behavior range are as follows: 1. Structural behavior can be calculated as a linear combination of different modes of vibrational structures that are independent of each other. 2. The vibrational time of the structure in each mode during the earthquake is constant. In this method, similar to linear static analysis, the response of the structure is multiplied by desired earthquake hazard level to match the maximum structural deformation with what is predicted in the earthquake. For this reason, internal forces in shapeable structures that have nonlinear behavior during an earthquake will be calculated larger than tolerable forces. Therefore, when examining acceptance criteria, the results of linear analysis are modified for structures that have nonlinear behavior during an earthquake. 1.4.3.1.3 Spectrum analysis method

The number of vibrational modes in spectrum analysis must be chosen so that the total percentage of effective mass participation for each stretch of earthquake stimulation in the selected modes is at least 90%. In addition, in each stretch, at least three modes of vibration and at least all modes that have vibration more than 4% of second must be taken into account. The design spectrum used in this method should be selected according to the rules. The results of any vibration mode should be done using known statistical methods such as (CQC) method or more precise methods that take into account the interaction between the modalities more precisely. The effect of earthquakes along the perpendicular to the desired length should be taken into account if necessary. 1.4.3.1.4 Time history analysis method

In analyzing the time history, the structure response is calculated using dynamic relationships in short time steps. In this method, the response of the structure under earth-accelerated stimulus must be calculated at least according to three accelerometers. If less than seven accelerations are selected for analysis, their maximum effect should be considered to control internal deformations and internal forces. In case of using seven accelerates or more, their moderate effect can be considered for controlling deformations and internal forces.

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1.4.3.2 Nonlinear methods • Nonlinear static analysis • Nonlinear dynamic analysis (time history) 1.4.3.2.1 Nonlinear static analysis

In this method, the lateral load caused by the earthquake is statically applied gradually to the structure, as the displacement at a specific point (control point) reaches a certain value (target shift) under the influence of the lateral load, and or structure collapses. For more information, see the Seismic Recovery Guide for existing buildings or the ATC-40 or FEMA356 instruction. 1.4.3.2.2 Nonlinear dynamic analysis

In nonlinear dynamics analysis, the structure response is calculated by considering the nonlinear behavior of the material and the geometric nonlinear behavior of the structure. In this method, it is assumed that the stiffness and damping matrix can be changed from one step to the next, but it is constant during each time step, and the model response under earthquake acceleration is calculated by numerical methods for each time step. Historically, engineers were reluctant to use nonlinear analysis methods due to complicated formulas and the long time needed for solving problems, but today due to some software capable of nonlinear analysis with finite element method with easy-to-use environment, this approach has evolved. In addition, developed problem-solving solutions and powerful computers have reduced the time to solve problems. In the past decade, engineers considered the finite element method as a valuable and inaccessible design method. However, designer engineers today are fully aware of the benefits of nonlinear analysis by finite element method and its use in design stages.

1.5 Identification of site specifications to investigate threats during seismic rehabilitation At the time of the building’s seismic reconstruction, there must be a widespread perception of constructional hazards. In this way the general

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specifications of the site are generally extracted using the following geological studies: • determining the urban area and location of the building along with location coordinates • examining the topographic conditions by determining site gradient You can use existing aerial maps to determine the city’s range. Otherwise, geographic software can be used to extract the geographic location as well as the target area and the topography and gradient of the site.

1.5.1 Identifying and determining the faults their distance from of the site In this section, one can determine the position, length, and types of faults based on the maps of the active faults of the area and extract their effect on the structure, and eventually use their effects to determine target of seismic rehabilitation.

1.5.2 Examining the fault risk In the fault phenomenon, the fault activity during an earthquake causes the layers of the earth to be displaced, thereby causing failure in the fault plane. The displacement occurs horizontally or vertically or in any case, which must be prevented from being located in this area or by the necessary measures to avoid damage to the building and installation. Therefore, to improve seismicity and access to fault information, available faults maps can be used.

1.5.3 Liquefaction history, high subsidence One of the most important damages that occurs at the time of the earthquake is the damages resulting from liquefaction phenomenon. This phenomenon happens when layers of soil lose their resistance against forces of earthquake and flow like fluids. In this case, due to the fact that the threshold of soil resistance is greatly reduced, it cannot bear the weight of the existing structures on its own, and sometimes it cannot bear its own weight. Liquefaction phenomenon generally occurs in areas where the soil layers are in saturated state. Soil liquefaction has occurred in many of the recent earthquakes such as the Alaska (Alaska, United States, 1964),

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Niigata (Niigata, Japan, 1964), Loma Prieta (Loma Prieta, United States, 1989), and Kobe (Kobe, Japan, 1995) earthquakes.

1.5.4 Differential settlement At the time of the earthquake, an asymmetric settlement of the foundation occurs due to the condensation of soil under foundation in some areas. This phenomenon is called heterogeneous settlement. The soil susceptible to liquefaction (or in other words, natural soil that is relatively loose or embankment that is not well-condensed) is prone to condensation and therefore subsidence (Fig. 1.53). Soil liquefaction tendency in the region can be examined in two ways for seismic rehabilitation. • By referring to examination results, notebooks, and geotechnical studies conducted at the time of construction and also liquefaction zoning maps. • By conducting new geotechnical experiments to determine soil liquefaction tendency. This issue will be discussed in details in the chapter related to the test agenda and quantitative evaluation.

1.5.5 Progressive or further liquefaction of soil This phenomenon is a type of liquefaction that occurs as a result of reloading in subsided soil in which static shearing stress is lower than the soil resistance. Deformations resulting from this phenomenon increase periodically regarding static and dynamic stress during an earthquake (Fig. 1.54).

Figure 1.53 Differential settlement.

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Figure 1.54 Progressive or further liquefaction of soil.

Figure 1.55 Boiling smooth sand.

1.5.6 Liquescence (boiling smooth sand) phenomenon One of the results of periodical liquefaction is lateral spreading of soil on low slope and smooth areas by the seas and rivers. For example, in earthquake in 1976 in Guatemala caused soil spreading across the riverbank of Montgó. In flat areas due to the high pour water pressure created by the liquefaction phenomenon, a rapid flow of water at the surface of the earth is created. This flow occurs both during and after the earthquake. If pore water pressure is high and fast enough, it moves the soil to cracks, and as a result, boiling smooth sand occurs. This phenomenon most often happens in areas affected by liquefaction phenomenon (Fig. 1.55).

1.5.7 Slipping phenomenon and slip types of mountain range • Transferring or simple slippage In transferring slippage, a mass of substance on a low slope or a smooth surface slides down the slope. Geological conditions and mainly

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Figure 1.56 Transferring or simple slippage.

structural fractures are some factors that create transferring slippage (Fig. 1.56). • Circular or rotatory slippage Circular or rotary slip is mainly seen on natural and artificial earth and sandstone slopes and less in slopes made of crushed or weak and weathered stones. In this case, the rupture occurs along the curved and spoon-shaped surfaces, which withstand the maximum shear stress. Generally, there is no need for special geological conditions and structural fractures to create a circular slippage. • Flat slippage in stone This slippage has many types, including slippage in one or more stone unit in one or more flat surfaces, slippage of one small or sheetshaped piece from stone onto a slope, slippage of big mass of stones, and finally wedged slippage along a common ground in two crossing sheets. In this type of slippage, spoon-shape mass of stones fractured along a cylindrical surface as a result of slippage. Creation of cracks in the head of the unstable part and the bulges on the heels are signs of initial movements. After fracture, there is usually a cliff on top of the slopes and disruptions below. Increase in slopes, weathering, and seepage water forces are some reasons for this type of slippage. Circular slippage is not seen in solid rocks. This type of fractures is often progressive and wide. Circular slippage in soil is the most common type of slippage in soil and circular movement of one or more parts is along the cylindrical surface. Suitable conditions for flat slippage • Layered sedimentary stones with slopes outward the slope with an equal or lesser amount of slope.

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• Faults, seams, and foundations that have weak long surfaces and cross the slope surface. • Crossing seams that create wedged fractures. • Hard and seamed stones that cause slippage of stone pieces. • Scaling in granite masses that cause the sheets of rock to slip. • Circular slip in the rock, the main causes of rotary slip in the soil.

1.5.8 Draught water forces The depth of fracture depends on the geological conditions. Deep slippages in clay earth and low-depth slippages happen in talus. The initial signs of this type of slippage are the tensile cracks at the top and bumps in the base of the slope (Fig. 1.57).

1.5.9 Lateral spread and sequential fracture This is a type of sheet fracture that is seen in stone and soil. Materials are laterally under stress along a weak surface, and sequentially break into pieces. The main reasons for this type of slippage include seepage water forces, increase in slope, and slope altitude. This type of fracture is usually unpredictable by mathematical methods since the location of first crack and therefore, the result of the first piece cannot be determined. However, since this type of fracture is created in special types of stones and soil, potential unsustainable state can be determined. Lateral spread

Figure 1.57 Draught water forces.

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Figure 1.58 Lateral spread and sequential fracture [4].

usually increases gradually and can have a high volume. This type of fracture occurs in river valleys and is seen in hard cracked clay and horizontal layers of low slopes (Fig. 1.58). That are on soil in situ or stone with mild slope, can sequentially cause lateral fractures. The sign of this type of fracture in the first stages is stretch cracks. Under some conditions such as loading as a result of earthquake can be abrupt during the progressive expansion, loaded stretch cracks and cliffs are created and final fracture may not happens in years.

1.5.10 Talus slope slippage This type of slippage refers to mass movement of soil, or soil and stones simultaneously or separately on a steep flat surface. This slippage is often progressive and may lead to avalanche or stream. The main reasons for this slippage are increase in seepage water force and talus slope. This type of slippage is created in places where taluses or residual soil are placed on a slope or relatively low-depth surface. This movement also starts with stretch cracks (Fig. 1.59).

1.5.11 Landslide Movement of some material on slope along a given fracture surface is called “landslide.” Buildings constructed on steep slopes where there is high underground water or there is high rainfall and the soil has a tendency to landslide, may lead to a lot of damage during an earthquake. The construction of vital arteries, especially bridges and tunnels, without regard to site studies, will lead to a lack of service in crisis situations. Landslide phenomena are generally occurring in areas with a high slope. Therefore, to better investigate this phenomenon, a general overview of

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Figure 1.59 Talus slope slippage.

Figure 1.60 Landslide damage [4].

landslides is presented. In slope slides, deformation is in the form of “simple shearing.” Slippage has different form and any types of material can be created. Characteristics of moving mass and shape of surface fracture are usually the criterion for categorizing slippages (Fig. 1.60).

1.5.12 Determining the type of land and underground water surface For seismic rehabilitation, examining and determining the type of land and underground water level is possible in two ways: • Referring to experiments, notebooks, and geotechnical studies conducted at the time of construction. • Conducting new geotechnical experiments to determine the type of soil (Fig. 1.61).

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Figure 1.61 Water cycle.

References [1] Iran Road, Housing & Urban Development Research Center, Iranian Standard 2800, Fourth Edition of Building Design Codes Against Earthquake—Standard 2800 of Iran. [2] Federal Emergency Management Agency (FEMA) (356), Prestandard and Commentary for the Seismic Rehabilitation of Buildings. [3] Islamic republic Vice Presidency for Strategic Planning and Supervision Office of Deputy for Strategic Supervision, Department of Technical Affairs, Code. No (360) first revision, Instruction for Seismic Rehabilitation of Existing Buildings. [4] Iran Road, Housing & Urban Development Research Center, Immediate Preliminary Inquiry Report of November 12, 2017, Kermanshah—Sarpole Zahab.

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CHAPTER TWO

Seismic rehabilitation steps and practical methods in seismic rehabilitation of existing buildings Aims By reading this chapter, you are introduced to: • • • • •

damage to existing materials; how to prepare the reports and information needed for seismic rehabilitation of existing buildings; get acquainted with a quick and detailed evaluation comprehensively of a building and its effective parameters; understand the tests and how to apply them to a variety of materials; and get acquainted with the methodology of presenting a seismic rehabilitation plan.

2.1 Seismic rehabilitation studies with applied approach One of the issues that engineers are concerned about is to design and construct structures resistant to earthquake and maintaining existing buildings. Therefore nowadays we are faced with development of earthquake engineering science in buildings. The materials provided in this field are mostly divided into two categories. First is the materials presented and provided for buildings in stages of designing and preparing structural plans. Second category is considered for the buildings that need to be seismically studied. This study is to determine the performance of a building during an earthquake. In this section, reliable methods for seismic rehabilitation for buildings are provided. An engineer faces a wide range of materials in the section which mainly include the materials presented in related regulations and technical knowledge from executed projects. These materials are mainly presented in the form of books, executed projects, and studies in great global engineering society. The wide expansion of seismic Seismic Rehabilitation Methods for Existing Buildings. DOI: https://doi.org/10.1016/B978-0-12-819959-6.00002-6

© 2020 Elsevier Inc. All rights reserved.

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Figure 2.1 2016 Kermanshah earthquake. Source: From https://commons.wikimedia. org/wiki/Main_Page

rehabilitation methods can be mentioned as an example. Thus, to build a mental model for a seismic rehabilitation engineer, the materials in the form of reports and resources must be categorized to enable the engineer to make proper decisions at the right time to guide the project and know how to start a seismic rehabilitation project, continue the related process, and eventually complete it. In this section, the practical manner of using the materials in construction projects is presented. Fig. 2.1 is the result of an earthquake.

2.1.1 Product and documentation of seismic rehabilitation studies This topic begins with the question of how to begin and finally achieve the seismic rehabilitation of an existing building. We assume that the reader is facing a building for seismic rehabilitation studies. In this assumption, there are related seismic rehabilitation regulations on one hand, and on the other, there is the building that must be evaluated after the project. The question is that how an engineer should treat seismic rehabilitation process so that he can determine a seismic rehabilitation plan for the building according to guides provided in regulations economically and local knowledge in a specified time. In this chapter, it is tried to provide a thorough cycle of details and documents by using

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author’s previous experience for the reader to better understand the material. Seismic rehabilitation process of an existing building includes three main steps: • complete vulnerability evaluation of the building; • providing seismic rehabilitation plan for the building; and • managing and executing seismic rehabilitation plan. A complete evaluation of the vulnerability of a building to identify potential damage to its structural and nonstructural components is not possible only by using seismic regulation guidelines. In this regard, the seismic rehabilitation engineer needs to collect and compile documentation for operations as in the following. To assess, in the preparation of a full evaluation report on the vulnerability of the existing building, the resident engineer must provide the following assessment manuals for the design engineer to provide a seismic reconstruction plan. 1. Collecting preliminary information on visiting the building. 2. Preparing qualitative evaluation of the existing building (the contents will be provided later). 3. Experiments and digging according to seismic rehabilitation objective and the type of existing building. 4. Qualitative evaluation report on seismic rehabilitation objective and the type of existing building. Also, to provide a rehabilitation plan for a building, the following topics must be discussed, and an appropriate notebook and manual should be prepared and documented for each. Finally, the notebooks should be handed to the engineer to design executing seismic rehabilitation plans. 1. Report presenting three options for refinement in accordance with the criteria and regulations for admission. 2. Report on the presentation of a detailed seismic rehabilitation plan taking into account the architectural and economic considerations of the plan. The project execution, management, and control department should provide the following items according to the prepared manuals and available guidelines. 1. Preparing phase 2 seismic rehabilitation plan in all executable levels. 2. Project execution manual. 3. Seismic rehabilitation schedule. 4. Financial flowchart and project scheduling (cash flow review) (Fig. 2.2).

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Figure 2.2 Collecting preliminary information.

2.1.1.1 Collecting preliminary information in visiting the building This stage is known as the most important stage in determining building vulnerability. The set of steps that have to be taken during project inspection are: 1. current status of structural components; 2. current status of nonstructural components; and 3. current status of adjacent buildings. An objective inspection checklist of the building is prepared according to instructions provided for seismic rehabilitation of existing building and construction conditions. This checklist is completed by the project expert and used for preparing qualitative report. At this stage, before qualitative evaluation of vulnerabilities, architectural plans must be drawn in details. These plans include the following items and are considered as the main plans until the seismic rehabilitation project is finished. • interior architectural layout of the floors with detailed finishing and brickwork; • plan of load bearing walls’ position in building; • plan of elevation in latitudinal and longitudinal directions which show architectural details of modeling direction in qualitative evaluation stage; • plan of adjacency with neighbors and surroundings of the building up to the distance that is influenced by adjacency; • plan of the facade in northern, southern, eastern, and western directions with all finishing and execution details; • plan of roof sloping and roof eaves with all details; and • plan of places of furniture and equipment. 2.1.1.2 Preparation of qualitative evaluation At this stage, we will analyze the quality of the building with regard to all the available information. It should be noted that all the information in

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the notebook and manual is based on engineering judgment and existing documentation. Therefore judging about the necessity or unnecessary of rehabilitation is put off to the next stage. At the final stage of the project, the expert must provide a checklist and a list of experiments to the soil mechanics and geotechnical consultant. In this part of evaluation, different issues are often considered. These include issues such as structural features of the building, features of the site in terms of seismicity risk, primary evaluation of seismic strength, history of building construction, use, and status, economic project-based considerations and evaluations. At final part of this stage, architectural plans are prepared and the structure is studied to prepare qualitative evaluation manual and agenda for experiments. In this section, the main purpose is to identify arrangement of the members and components of the gravity load-bearing system and the lateral load-bearing system resistant against earthquake force. • Determination of structural and nonstructural members that are effective in the stiffness and seismic performance of structures. • Specifications of the site. • Effects of adjacent buildings. The quality assessment manual generally includes the structural design specification. In the designation of structural and nonstructural members that are effective in the stiffness and seismic performance of the structure, all the specifications specified below must be fully extracted based on objective observations and review of existing plans, to provide a checklist of rapid vulnerability evaluation of the building and quantitative evaluation manual. • specifications of the building; • building history and future uses (Fig. 2.3); • geographical position and construction year; • building use and performance of parts and spaces; • the type of materials and ceiling;

Figure 2.3 Cycle of operation change over the useful life of the building.

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Figure 2.4 Regularity or irregularity of the building.

• • •

geometrical dimensions and the number and height of the floors; regularity or irregularity of the building in plan and height [1] (Fig. 2.4); stairways position, accessing floors, nonstructural components, and emergency stairs; • lateral and gravitational load-bearing systems in the building; • symmetry of the building plan (in terms of mass and stiffness); • occupancy and protrusion position in the plan; • position of opening surfaces and their adjacency to floor diaphragm; • separation connection conditions; • position of separating walls and facade walls; and • general position of visible damages in components and components. It should be noted that in this report, there is no evaluation of the above with regard to the existing regulations, and finally the conclusions are made later at the end of the report based on the documentation of the checklist. In the section of the building’s specifications, in accordance with the provisions of section, it is necessary to complete the following: • general specifications of the site; • seismic risk; • examining the type of land and determining underground water levels; • Landslide; • type of slope slides; • records of liquefaction and regional subsidence; and • primary objective inspection of strength. The assessment of the status of adjacent buildings is very important in the qualitative assessment report. In this section, the following items are considered: • Investigating the collision of neighboring buildings during earthquake: In the event of an earthquake, if there is a risk of collisions between two adjacent buildings, this collision may lead to local breakdowns of

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•

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structural components at the site and the destruction of nonstructural components. In this case, there is no possibility of special rehabilitation for the studied structure. Investigation of structural and nonstructural connection components between two neighboring buildings: first, if there are common parts between the two neighboring buildings, these components should be identified and reviewed in plans and studies, because the presence of these connection components causes structural failure for the following reasons: 2 leading the removal of part of the adjacent building; and 2 leading to unforeseen forces in neighboring buildings. Pathology caused by nearby buildings: In the event of an earthquake, many buildings that are seismically resistant to this force may be vulnerable due to the weakness of neighboring buildings and their destruction. The rehabilitation expert must inform the operator of the potential hazards of the neighboring buildings and insert the necessary measures in the reports.

2.1.1.3 Experiments and digging Performing the required experiments is one of the most important parts of the seismic rehabilitation of the building. In this section, the experiment and digging agenda will be prepared according to the configuration based on the quality assessment report and will be provided to the corresponding unit. The importance of this section is all reviews are based on the results of the experiments. Therefore inaccuracies increase costs or provide inappropriate design for improvement. It should be noted that the drawings are made at this stage after the digging and are set for use in the quantitative report. Experiments and digging agenda for seismic improvement of existing buildings generally include the following: • digging and member destruction; • identification and recognition; • material strength experiment; • geotechnical experiments; and • reconstruction of the digging site and experiments. This is discussed in more details later on due to the high importance of the subject. 2.1.1.4 Report of quantities evaluation In this section, building modeling is done based on the results of experiments, plans, digging, and objective inspections. This modeling will be

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carried out in accordance with the criteria set out in the Seismic Rehabilitation Journal of the existing buildings used for the project. Finally, its modeling is done in the form linear and nonlinear analyzes by using computational software. In this report, the strength and component capacity are determined based on the results of numerical experiments and calculations and are used to determine the vulnerability. After analysis, overall conclusion on the performance of the existing building according to necessity and unnecessary for rehabilitation and considering weaknesses of the studied building are provided based on a table in different parts of the report. The evaluation of nonstructural components is one of the chapters of this report. At this stage, by determining some conditions, studies can be stopped and orders for rehabilitation or destruction of the building can be provided by the design consultant. The configuration of the quantitative evaluation is in the following. 2.1.1.4.1 Quantitative evaluation of the building

At 1. 2. 3. 4. 5.

the floors level: Quantitative evaluation Quantitative evaluation Quantitative evaluation Quantitative evaluation Quantitative evaluation At foundation level: 1. Quantitative evaluation 2. Quantitative evaluation

of of of of of

beams. columns. connections. walls. nonstructural components.

of foundation. of soil in site under the foundation.

2.1.1.5 Report providing on three-method for seismic rehabilitation of existing building In this report, for the building under study, we should offer three rehabilitation options with a complete computer modeling. Also manual calculations, financial estimates (Cash flow), and The time required to implement each option (Time flow) are provided in detail. Finally, one of the options is chosen by compare the run-time and financial estimates as the preferred option for the final design. 2.1.1.6 Report on providing a detailed seismic rehabilitation method for top method In this report, the superior option is fully modeled in the form of software analysis using computer modeling and numerical computations and the

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Figure 2.5 Seismic rehabilitation process flowchart.

results are evaluated. The Detailed cash flow required for project implementation is also prepared in this report. At the end of the report, plans containing executive details for the top method are provided. The timetable for the project management is provided to the operator. Fig. 2.5 is the process of preparing reports for a seismic rehabilitation.

2.1.2 Introducing seismic rehabilitation regulation and its scope for this book The topics in this book are presented according to seismic rehabilitation standard for existing buildings: FEMA 356 and Instruction Standard

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Seismic Rehabilitation Iranian Codec No. 360. In these instructions, evaluation methods for existing load-bearing systems and seismic rehabilitation solutions are provided for buildings to improve performance during earthquake and reach a target performance level. However, restoration of damaged building after an earthquake is excluded from this instruction. Regarding that the provided examples are related to projects in Iran, and materials presented in this book are aimed at reaching a desirable performance level according to the instructions. Therefore earthquake-related parameters in relevant regulations are used for simplification. Application range of the materials in this book is according to publications on evaluation of buildings that have not been damaged during earthquakes. These materials are: • Basics of seismic rehabilitation Including application range, basics, stages, aim, performance levels, and earthquake risk analysis. • Collecting documents and information, understanding the status Including application range, building status information, information levels, material strength, collecting information about soil, foundation, and structural and nonstructural components. • Analysis methodology Including application scope, general criteria for analysis, analytical methods, structural components capacity, and acceptance criteria. • Site and foundation Including application range, site hazards due to instability, lateral seismic pressure of soil, and foundation rehabilitation. • Structures, steel and concrete components, and masonry materials Including application range, criteria and evaluation assumption, types of building frames, seismic systems, structural components, types of masonry walls, modeling requirements and structure analysis, examining wall behavior, and infrastructure built with masonry materials. • Diaphragms and infill frames Including diaphragms, classifying diaphragms in terms of rigidity, and types of infill. • Rehabilitation of nonstructural components Including application range, aims, interactions, classification, and rehabilitation methods, architectural, mechanical, and electrical components, and interior equipment.

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Building features including structural and nonstructural component specifications, earthquake risk at the site, results of primary evaluation of seismic strength, history of past uses and future uses of the building, special economic and social considerations, and governing rules, with users’ comments must be provided for the seismic rehabilitation engineer before any rehabilitation measurement. Also in Chapter 3, Types of Existing Buildings: Detailed Introduction and Seismic Rehabilitation, given that the selected examples relate to the country of Iran and the earthquakes that occurred, the fourth edition of Building Design Codes Against Earthquake standard 2800 is used to select geographical assumptions.

2.2 How to determine the strength of materials available in existing buildings The evaluation of the specifications of the building materials can be done in two ways: 1. visual assessment of the quality of materials; and 2. laboratory and digging procedures. Each of the following will be described in general terms. Chapter 3, Types of Existing Buildings: Detailed Introduction and Seismic Rehabilitation, provides full details of each buildings type.

2.2.1 Visual assessment of the quality of materials Some problems can be evaluated in the visual inspection of the materials in the building, but the scope of the use of this information is limited to use in the rapid quality assessment report of the vulnerability. Quality of materials and quality of implementation is an important indicator of building evaluation, which can be reviewed by an expert specialist. This is the most basic and the simplest method of monitoring a structure in which a skilled person visually inspects and identifies the damages in the material of the structure. Therefore, in this section, the visual inspection of the quality of materials and performance for three categories of materials are presented, which will be discussed further. • Pathology in concrete materials. • Pathology in steel materials. • Pathology in traditional building materials.

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2.2.1.1 Pathology in concrete materials Factors affecting erosion and concrete degradation may be caused by various causes. Different reasons cause erosion and destruction of concrete structures. These reasons are in the following. 2.2.1.1.1 Ingress of salts

Salt deposits that result from evaporation or salt in flowing waters, as well as salt that is accumulated in porosities and cracks, can apply damaging pressure to structures while crystallizing in addition to accelerating and exacerbating corrosion and erosion in reinforcements. Alternating wetting and drying can also increase the concentration of salt, since salt is left after water evaporation. This is one of the most important factor in bars. This issue is mostly seen in sea docks (Fig. 2.6). 2.2.1.1.2 Designing errors

Application of inappropriate standards and incorrect technical specifications regarding the selection of materials, methods of operation, and performance of the structure can lead to concrete failure (Fig. 2.7). 2.2.1.1.3 Construction errors

The errors and defects that occur during the execution of the projects may lead to damages such as honeycomb phenomenon, bleeding concrete, detachment, accumulation crack, additional empty spaces, or contaminated concrete that all cause serious problems. Such defects can be attributed to efficiency, degree of compaction, treatment system, contaminated water juice, contaminated aggregates, and misuse of additives individually or in groups (Fig. 2.8).

Figure 2.6 Ingress of salts in concrete.

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Figure 2.7 Designing error in concrete building.

Figure 2.8 Construction error in concrete building.

2.2.1.1.4 Fire

Three main factors can determine the strength of concrete to high heat. These factors include: 1. Ability of concrete to withstand heat, and water proofing is achieved without cracking, collapsing, or strength reduction. 2. Conductivity. 3. Heat capacity. It is noted that two completely opposite mechanisms of expansion and shrinkage are responsible for the failure of concrete against heat. While pure cement expands when it is exposed to high temperatures, concrete in the same conditions, tends to shrink and shrink. Because the heat causes the loss of concrete water, the amount of contraction as a result of the drying action exceeds the amount of expansion and causes the shrinkage to occur, followed by cracking and concrete collapsing.

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Concrete exposed to up to 100
C is normally considered as healthy. The parts of a concrete structure that are exposed to temperatures above approximately 300
C (dependent of water/cement ratio) will most likely get a pink color. Over approximately 600
C the concrete will turn light grey, and over approximately 1000
C it turns yellow-brown. One rule of thumb is to consider all pink-colored concrete as damaged that should be removed. If concrete is exposed to very high temperatures very rapidly, explosive spalling of the concrete can result. In a very hot, very quick fire the water inside the concrete will boil before it evaporates. The steam inside the concrete exerts expansive pressure and can initiate and forcibly expel a spall. 2.2.1.1.5 Chloride attacks

The presence of free chloride in concrete will damage and eliminate the inactive protective layer around the reinforcement (Fig. 2.9). Chloride corrosion of the reinforcement in the concrete is an electrochemical process that provides the required concentration of chloride ions, anode and cathode regions, the presence of electrolytes, and the flow of oxygen to cathode regions in the corrosion cell. 2.2.1.1.6 Sulfate attacks

Sulfates that are soluble in contact with cement can cause chemical changes in the cement, and this may lead to significant microstructural changes that lead to weakening of the cement glue. Sulfate solutions can also cause damage to porous cement through crystallization and recrystallization (Fig. 2.10).

Figure 2.9 Chloride attacks in concrete material.

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Figure 2.10 Surface attacks in concrete material.

Figure 2.11 Frost actions in concrete.

2.2.1.1.7 Frost action

For wet concrete, freezing is a deterioration factor, as water becomes excessive in mass during freezing and produces internal stresses and thus concrete is cracked. The cracks and seams that are the result of alternate freezing and melting cause the surface of the concrete to become flaky and damages become deeper as a result of corrosion. Therefore the freezing of concrete and the rate of degradation depend on the degree of porosity and the permeability of the concrete, which are in addition to the effects of cracks and seams (Fig. 2.11). 2.2.1.1.8 De-icing salts

If de-icing salts are used to melt the concrete ice, in addition to the damages resulting from freezing, these salts may also cause surface damage to the concrete. Because it is believed that breakdowns from de-icing salts occur as a result of a physical action (Fig. 2.12).

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Figure 2.12 De-icing salts in concrete.

Figure 2.13 Carbonation of concrete.

2.2.1.1.9 Carbonation

Carbon dioxide in the air can react with the calcium hydroxide present in the concrete and produce calcium carbonate. This process is called carbonization, the carbonation of the concrete process is slow and continuous from the outer surface to the inside and has slower penetration when depth increases. Carbonation has two consequences: It increases the mechanical strength of the concrete, but also reduces the alkalinity required to prevent the erosion of steel bars. At a pH value of less than 10, the thin layer is dissolved and corrosion progresses. Because of the second result, carbonation is an unwanted phenomenon in concrete chemistry. The effects of the above factors on the components are visible to the naked eye so that they appear in the form of color and separation of particles, flakiness, etc. In general, among the factors above, the two factors for detecting concrete damage are as follows (Fig. 2.13).

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Figure 2.14 Alkali-aggregate reaction in concrete material.

2.2.1.1.10 Alkali-aggregate reaction

Here alkaline-silica and alkaline-carbonate reactions can be mentioned. Alkali-silica reaction is: A gel is obtained from the reaction between potassium hydroxide and reactive silicate in aggregate. Due to water absorption, this gel expands and creates tensions resulting in the formation of internal cracks in concrete. Alkali-carbonate reaction occurs between alkali in the cement and a certain group of limestone (dolomitic) in a wet state. In this case, the resulting expansion causes cracks or bends in thin sections (Fig. 2.14). 2.2.1.1.11 Separation of concrete particles

Separation of particles is a phenomenon that occurs in fresh concrete, so that the coarse particles of the mixture reside and the smaller particles move upward. Therefore the concrete loses its uniformity and the distribution of aggregation is disturbed. Separation of particles in fresh concrete is an undesirable phenomenon. A concrete in which particles are separated will be weakened in terms of pressure and flexural strength and will not reach the desirable level. The most important reason for particle separation in fresh concrete is high slump. Other reasons such as excessive vibration or the displacement of concrete in the frame by a shovel or vibrator or the pouring of concrete from a height may also result in the separation of particles. Inappropriate storage of particles may result in the separation of particles before the construction of the concrete and, possibly, lead to the absence of uniform and correct aggregate in the concrete (Fig. 2.15).

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Figure 2.15 Separation of concrete particles in concrete material.

Figure 2.16 Bleeding in concrete material.

2.2.1.1.12 Bleeding

This visual phenomenon appears in a way that after pouring concrete and surface finishing, a thin layer of water with concrete appears on the surface of the concrete. This water moves from levels underneath to upper parts due to capillarity feature and probably washes some cement on the way. Therefore, in the upper parts of the concrete, the amount of water used in the mixing plan will be greater, and the amount of water in the lower parts of the concrete will be lesser. Bleeding concrete is damaged after hardening and will not be desirable. The upper layer of bleeding concrete after hardening turns into powder in time and by using and changes to dust, therefore, the surface layer will not be smooth and powdering phenomenon. Such concrete is first unsightly and second is a weakness for frost and weathering conditions (Fig. 2.16).

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2.2.1.2 Pathology in steel materials Today, various steels are used in buildings in various ways, and for this reason, the corrosion problem in steel material buildings is immense. So that corrosion control is very important in steel structures. 2.2.1.2.1 Corrosion

Corrosion refers to any process that causes erosion or corrosion of metal components, and the most common example is metal rust. Corrosion processes are often electrochemical. In common building corrosion, there is often a type of metal involved with water that has dissolved a little salt (as an electrolyte). Other factors, including specific bacteria in the soil, which absorb hydrogen, may also act as depolarizing agents and contribute to the development of corrosion reactions. The metal components used in buildings can be divided into four groups according to the possibility of corrosion: • Steel used outside the building as superficies, roof covering, sunblind, and canopies. • Steel used in structure skeleton as structural steel or in combination with building material. • Steel used in building facilities such as plumbing, hot water reservoirs, canals, etc. • Steel buried beneath soil. 2.2.1.2.1.1 Corrosion of steel outside building structure Steel that is used outdoors is exposed to atmospheric conditions. The main atmospheric factors affecting the corrosion of steel are temperature, sulfur dioxide and chloride pollution, and the time metal remains wetted by the moisture content. By measuring these variables in different regions, a comparison can be made between the corrosion rates of the metal at different points. A suitable method for this purpose is to place samples of different steels in different regions and determine the amount of corrosion of the metal using the amount of weight loss after cleaning the metal. This experiment has shown that the corrosion rate is very different in different regions and for various steels. Such experiments are used only as guides to calculate the corrosion of steel if it has applications such as roofing, canopies, and stucco; because designing techniques can effectively limit the visible surface of steel. For example, protrusion of roof can protect wall coverings from high humidity, snow, and rain. Such practices should be

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Figure 2.17 Corrosion of steel outside building structure.

applied as much as possible, as they can protect the metal against corrosion. In designing roofs, aqueduct, and rainspouts, effort must be taken to prevent any seam (gap) or vent in which water is accumulated and held for long because corrosion continues as long as metal stays wet. Such design techniques are of high importance especially in bridges, towers, and other structures with visible steel. Kennels also has to be paid attention to since water can be accumulated in them and serious corrosion might happen due to being exposed to humidity, snow, and rain. It can be stated that inappropriate design is the primary important factor that leads to metal and steel corrosion in buildings (Fig. 2.17). 2.2.1.2.1.2 Corrosion of inner-structure steel in a building Structural steel is usually considered as the most commonly used materials in buildings. Fortunately, steel is placed inside the structure, covered with ceiling and other covers and built on the surface, and thus separated from inner and outer environment. In cases where structural steel is exposed to water (either from penetration of rain or condensation of water evaporation), corrosion occurs, therefore structure must be at risk (Fig. 2.18). 2.2.1.2.1.3 Corrosion of steel inside concrete and masonry materials Arming steel and prefabricated steel are the most commonly used steels in buildings. Inner conditions of mass concrete and mortar are desirable for steel, and many old concrete structures confirm proper and appropriate performance. However, there are cases that show corrosion and weakness in performance of steel inside concrete and mortar (Fig. 2.19). 2.2.1.2.1.4 Metal corrosion in facilities of building A group of steels are used for facilities in buildings. The facilities that have serious corrosion

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Figure 2.18 Corrosion of inner-structure steel in a building.

Figure 2.19 Corrosion of steel inside concrete and masonry materials.

are: heating, water, and sewage disposal systems. Heating systems face corrosion problems due to water vapor or hot water transferring. If water is not appropriately purified and not purified at all, corrosion may occur in boilers and lead to catastrophes consequently. Condensed return pipes usually cause several problems due to the presence of oxygen or carbon dioxide. Using hot water in contact to radiation heating panels can be problematic due to corrosion of coil. In warm water heating systems, corrosion of pipes can also cause problems. Prohibition of using different materials in a system to prevent galvanic corrosion at contact points is a wise warning. Some anticorrosion substances such as phosphates or silicates can be used to decrease corrosion as a result of being exposed to water (Fig. 2.20).

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Figure 2.20 Metal corrosion in facilities of building.

Figure 2.21 Corrosion steel buried in soil.

2.2.1.2.1.5 Corrosion steel buried in soil Some metal components of buildings such as baseplate and water and sewage pipes might be buried in soil. The corrosion rate of steel is variable in different types of soil. Issues related to serious corrosion might increase due to special bacteria existing in soil. These bacteria are usually found in clay soil and mud in riverbeds and lakebeds. Engineers must be very scrupulously since damage resulting from corrosion of material in soil is not visible until it is too late and changing the damaged components is much too costly if possible. Cathode protection using forced electricity flow besides using asphalt coating is usually the best method to protect steel in the soil in cases where corrosion conditions exist in soil. In addition, soil-filling substances must not be applied since they may contain compounds with corrosion effect (Fig. 2.21).

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2.2.1.2.2 Fire in steel construction

Fire is a phenomenon that every structure in its useful life may experience. With the development of modern urban development, the potential for fire hazards and the likelihood of them occurring in structures has also expanded. What is important is how to prevent and deal with fire hazards in buildings, which should be highly regarded (Fig. 2.22). 2.2.1.2.3 Designing error in steel structure

Steel buildings are highly resistant and resilient if properly designed and executed correctly, but due to the lack of expert executive forces and the wrong assumptions of steel structures, they have disadvantages and drawbacks that require reinforcement and are improving. Steel buildings are often under seismic loads due to damaged local buckling and poor performance (Fig. 2.23).

Figure 2.22 Fire in steel construction Plasco building in Iran.

Figure 2.23 Designing error in steel structure.

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2.2.1.3 Pathology in traditional masonry materials Buildings with masonry materials are the ones in which load-bearing structure is a wall and in which main components are bricks and similar materials. Therefore brick and its specifications and damages are discussed here. Know brick as the most important masonry building materials: Generally brick is the building material used to make walls, pavements, and other components in masonry construction. Traditionally, the term brick referred to a unit composed of clay, but it is now used to denote rectangular units made of clay-bearing soil, sand, and lime, or concrete materials. Bricks can be joined together using mortar, adhesives, or by interlocking them. Bricks are produced in numerous classes, types, materials, and sizes which vary with region and time period, and are produced in bulk quantities (Fig. 2.24). Using brick as building material is an ancient method. The clay bricks are the first and most common bricks the highest use in thousands of years. Bricks can be tightly used next to each other due its dimensions. This feature creates several engineering qualities such as Junction of two walls. These features have enabled building wide openings in bow shape, arch shape, and dome from Sassanid dynasty in Iran. Features of brick has made it the most used material to fill walls, ceilings, etc. Strength, beauty, and pattern resulting from brickwork are main reasons that bricks are used inside the building and outside as facade bricks give the building a special identity. Damages in materials and components that are visible to naked eye are as follows: • Corrosion in consumable materials In case digging is not performed on structural components, the corrosion rate cannot be understood. Therefore, in this section of qualitative report on vulnerability, if there is visible damage in structure, damages

Figure 2.24 Brick material.

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can be stated according to a table separating the materials and type of component damages. This corrosion includes breaks in materials, Breakdown in the place of materials, cracks in materials, and in place of masonry materials. Design defects and execution problems It is not possible to certainly know about design defects and executions before digging, from qualitative report on vulnerability regarding the construction year and visual inspections. Therefore type of skein, position of openings, plan dimensions, and other visual items can be referred to as design effects according to the regulations and criteria of construction year.

2.2.2 Quantity evaluation with experiments and digging results One of the most important stages of seismic rehabilitation studies is experiments. Thus, to determine and report on the digging of the experiments, after setting up a qualitative assessment manual, appropriate digging agenda with sufficient number of experiments should be arranged by the planning expert. Steps to prepare dig and restoration agenda are as follows: • general experiments of familiarity with experimenting and digging; • general knowledge of complete familiarity with repair and restoration; • preparation and setting of the agenda, preparation of experiment tables for each level of the building; and • preparation and setting of the agenda for providing comprehensive plans where the site of digging and experimenting are included. This section describes how to conduct experiments and digging, as well as repair the desired sites. Full evaluation of the results of the experiments. Detecting the specifications of consumable materials in the building should be done in the following ways: • digging and component destruction; • identifying and detecting; • experiments of material strength; • geotechnical experiments; and • repairing (Table 2.1). Experiments and digging services have a high importance in seismic rehabilitation studies, and qualitative evaluation and vulnerability studies

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Table 2.1 Required components specification. Additional specification required

Dimensions and thickness of components and covering sheets, braces, and stiffener Status, execution, and specifications of connections and patches Cross-sectional area, cross-sectional basis, inertia moment, and torsional properties of members in critical sections The physical conditions of the base metal and the components of the connections including the examination of existing deformities and damages

Row

1 2 3 4

Figure 2.25 Chart of seismic rehabilitation studies from the perspective of geotechnical services.

are based on the results of such studies. Therefore the order of performing, range, number, and type of experiment are very important. Flowchart for studies of side services are as follows. According to regulations in seismic rehabilitation instructions for existing buildings, the number, site, and type of experiments and digging must be determined. Engineers of seismic rehabilitation must determine and provide experiments and digging agenda for the related technicians, be present during experiments, studies, and finally confirm the process and receive the related report (Fig. 2.25). 2.2.2.1 Destruction and digging The operation of removing thin coatings in the position of target components to access and prepare components for sampling and destructive and nondestructive experiments is called destruction and digging.

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Table 2.2 Destruction and digging of components. Row Position Description

1

Connection

2

Column

3

Beam

4

Roof

5

Shallow and deep foundation Wall

6

7 8 9 10 11

Cover concrete (rebar cover) Ceiling Retaining wall Stepped ceiling Other nonstructure component

Digging and removing cover at beam-to-column connection until accessing details (through ceiling and walls) Digging and removing cover at column until accessing details Digging and removing cover at beam until accessing details (concrete and steel) (through ceiling and walls) Digging and removing cover at roof to access various members or components and structural connections and identify the roof system Digging and removing cover at the foundation to access shallow and deep foundation detail Digging and removing cover at the wall (masonry and concrete material) to access shallow and deep foundation detail Digging and removing cover concrete to access longitudinal and shear rebar in position Digging and removing cover Digging and removing cover Digging and removing cover Digging and removing to access detail

The size and position must be such that the effective identification and observation of components or connections are possible. Choosing the place of destruction should not cause serious damage to the structure. Concrete should be destroyed to determine the profile and condition of the reinforcement used in the members or parts. During the course of destruction and digging, the equipment that causes pollution in the environment in case of damage must be relocated from the site (Table 2.2). 2.2.2.1.1 Digging building components

This section describes how to conduct experiments and digging, as well as repairing the desired positions. As mentioned in previous articles generally a building is composed of three categories of materials. Section build with concrete, steel, and masonry. Also this section introduces the important of the building that should be digging and experimented.

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Figure 2.26 Digging foundation under wall.

2.2.2.1.2 Digging foundation

Foundation digging is performed to determine the depth of placement, dimensions, and the type of foundation and to determine the arrangement of reinforcement. Sampling from foundation reinforcements and tensile experiments of rebar is done to determine surrender tension, and the final tension of foundation bars and coring from foundation concrete is done to determine pressure strength of concrete. After this step, the interpretation and review of the results in the quantitative phase report are used and evaluated (Fig. 2.26). 2.2.2.1.3 Digging columns and vertical tie

Digging columns is performed to determine dimensions of columns, their placement inside walls, their connection to the wall, and finally type of columns and drawing as-built plans (Fig. 2.27). 2.2.2.1.4 Digging beams

Digging beams such as structural or nonstructural is performed to determine dimensions, types of joins, and other details required for drawing structural as-built plans. Digging lintel is performed to examine lintels and determine span and related profiles, and how they are placed on walls. The digging must not cause instability of panel part in lintel (Fig. 2.28). 2.2.2.1.5 Digging connections

This digging is performed to examine types of connections, components, solder, and other factors important for drawing as-built plans.

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Figure 2.27 Digging tie in walls.

Figure 2.28 Digging lintel beam upper windows.

2.2.2.1.6 Digging roof in diaphragm

Digging roof is performed to determine specifications of stringer throughout the floor, and bearing beams in corridors, roof CBF PLATE, type and diameter of brace bar, and to perform tensile experiments on profiles and drawing as-built plans. 2.2.2.1.7 Digging masonry material component

This digging is performed to examine brick, mortar, etc. Note: If there are ways to access the floors, a digging is required to fully identify the details in the form of a plan.

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2.2.2.2 Experiments and identification of the existing building components This step involves determining the visual characteristics and geometric details of the members and the various structures in the buildings. Finally, the plan of the status of the existing as-built structure at this stage is drawn up according to the identifications. 2.2.2.2.1 Methods of experimenting

Based on the seismic improvement guidelines for existing buildings, common methods for measuring the properties of materials and fittings require the experiments of material strength, which include two methods, destructive and nondestructive methods aimed at the following: 1. Drawing up and completing existing as-built structural plans. 2. Determining all specifications of materials used in the structure. 3. Determination of weaknesses and comprehensive damages of materials in structures. The following describes two methods of destructive and nondestructive experiments. Some common practices are also mentioned (Table 2.3). 2.2.2.2.1.1 What is destructive methods? A destructive test commonly used to measure the mechanical strength of materials are more accurate than nondestructive tests for testing purposes. This type of testing is usually justified in cases where a piece has been used extensively in an existing building, and the loss of a small number of samples to control quality does not pose a problem for building performance level. In some cases, such as earthquake engineering or automotive design, expensive samples may also be tested in destructive tests to ensure the performance of other samples. Experiments in this method require sampling. These experiments include coring of concrete, cutting mortar, tensile experiment, etc. Table 2.3 Some destructive experimenting methods. Row Conventional

1 2 3 4 5 6 7 8

Coring concrete Rebar strength Mortar shear strength capacity Tensile strength of steel Shear strength of steel Flexural strength of steel The experiment required to estimate the specificity of the concrete Compressive strength of masonry materials

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2.2.2.2.1.2 What is nondestructive methods? Experiments that do not require destruction of the component, or require a limited amount of destruction, are called nondestructive methods. Conducting such experiments do not cause decrease in shelf life of components (Tables 2.4 and 2.5). For example, in determining the strength of concrete, technical approaches are compared to the destructive and nondestructive methods based on Table 2.6. 2.2.2.2.2 Experiments of material

Subsequently or simultaneously with identification, a visual inspection of the structure and the exact determination of the number of destructive and nondestructive experiments are performed in this stage. Experiments in existing buildings are mainly divided into two categories: 1. materials strength experiments; and 2. soil mechanics experiments. Materials strength experiments Strength experiments of materials in existing buildings are mainly divided into three categories: 1. experiment on concrete components; Table 2.4 Some nondestructive experimenting methods. Row Conventional

1 2 3 4 5 6

Visual (optical) experimenting Dye penetration Magnetic particles Eddy current Ultrasonic Radiography

Nonconventional

Neutron radiography Thermal and infrared Acoustic emission

Table 2.5 Some nondestructive advanced experimenting methods. Row Experimenting name Application

1 2 3 4 5

Penetration strength method Penetration frequency method Radioactive Radiometry Nuclear method Radiometry-gamma- neutron Stress wave Concrete resistivity

Strength estimation Concrete property • Density • Thickness • Moisture content Rebar property • Size • Position • Corrosion

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Table 2.6 Comparison of methods for the estimation of destruction of nondestructive concrete. Method Cost Rate of Degree of Ability to experiment destruction interpret

Coring Ultrasonic Schmidt hammer

High Slow Middle Fast Low Fast

Middle No damage Possible

Reliability

Middle Good Good Weak Just on concrete Weak surface

2. experimenting on steel components; and 3. experimenting on building materials if used as structural components. Soil mechanics experiments The soil mechanics experiments carried out at the level underneath the foundation in existing buildings are mainly divided into two categories: 1. in situ experiments; and 2. geotechnical studies. 2.2.2.2.2.1 Determining the mechanical specification of materials To determine the material specification, different experiments must be done on available materials. The mechanical properties of different materials are measured by applying different external forces. These properties determine the behavior of different materials in different conditions and are therefore very important. Mechanical properties of a material are stiffness, strength, elasticity, crunchy plasticity, fatigue, impact strength to creep wear. The materials used in the building are affected by various forces. Some materials show good strength to one force but weak to other forces. Therefore, when using materials, their strength must be measured against all forces in place. Types of mechanical resistors include: • compression strength; • tensile strength; • flexural strength; and • impact strength. The mechanical strength of various building materials is measured in the laboratory according to standards. 2.2.2.2.2.2 Material strength experiments In complete evaluation of vulnerability of existing buildings, to determine mechanical specifications of materials and joins, it is necessary to understand yield tension, final tension, pressure strength, tensile and shear strength, and other characteristics

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of materials. Also, as mentioned before, the criterion for collecting information on materials’ specifications and categorizing them is the objective for rehabilitation and type of analysis and finally reaching knowledge factor. Standards used for determining materials’ mechanical specifications are as follows: • Standards published by Standard & Research Institute for experiments such as ASTM. • Documents from International Standard Organization. The results of the experiments provide two main parameters: • Expected specifications of materials are equal to values from experiments. • Lower-bound strength of materials are equal to expected specifications of materials without considering standard deviation resulted from experiments. 2.2.2.2.2.2.1 Evaluation of concrete strength In this section, we will review

the potential options and practical solutions for on-site evaluation of concrete strength. Concrete (compressive) strength is by far the most important property of concrete. It represents the mechanical properties of concrete; for example, the 28 days’ compressive strength of concrete cylinders is the key parameter in most design codes (ACI 318-14, CSA A23.3-14). Strength is also considered (at least in the old school) a key factor for durability performance. On-site evaluation of concrete strength is a main challenge in the condition assessment of existing infrastructure. Owners and managers of such facilities prefer nondestructive methods to avoid further damage to an already struggling structure (Fig. 2.29).

Figure 2.29 Concrete.

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Destructive experimenting methods Compression experiment on concrete cores Semidestructive coring is one of the most accurate methods among the in-situ experiments, and extensive studies in this area provide the best evidence of the importance of this method (Fig. 2.30). Although this method is costly and slow compared to other in situ tests, its reliability justifies these disadvantages. The coring is done by diamond drill, and the cut cylindrical specimens are tested. Core strength is usually lower than standard specimen strength, which is probably due to drilling operations and differences in laboratory conditions with laboratory conditions. The cores used for compressive strength experimenting may have different diameters. The ASTM standard recommends diameters of 100 mm (3.93 in.) and 150 mm (5.90 in.). However, in some countries, such as Switzerland and Germany, cores with diameters of 75 mm (2.95 in.) and 50 mm(1.96 in.) are also permitted. But most research has shown that the impact of diameter on the measured strength is negligible and can be ignored. Coring and experimenting for strength might the first and most reliable solution. In this case, concrete core is taken from the existing structure. The core needs cutting (sawing) and surface preparation. The core is experimented for compressive strength. Benefits of this method 1. This is the most reliable method to estimate the compressive strength. The method is relatively fast. Disadvantages of this method 1. It is destructive. Not only it damages concrete integrity, it might affect reinforcing bars in RC structures. Rebar locating tools are needed to avoid this problem.

Figure 2.30 Coring concrete.

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2. Selecting experiment positions can be difficult. Selecting the best position of cores is relatively subjective. 3. The positions of cores needs to be repaired. 4. Coring is not an option for owners of important structures, especially when there are concerns about further damaging the structure. Pull out experiment The concept of tensile experimenting is based on the measurement of the force required to pull a circular steel disk 25 mm (1 in.) in diameter and 8.5 mm (0.33 in.) thick in concrete. The experiment involves a steel rod attached to a metal disk. This disk is placed at a depth of 2.5 cm (1 in.) on the concrete surface. During experimenting, the rod is removed from the disk and concrete and replaced with a hard steel screw. The hand hydraulic jack is then mounted on a concrete surface with an annular support of 55 mm (2.16 in.) in diameter and then the nut under the jack is attached to the steel screw and exerts a tensile force of about 1060 kN (2.2511.25 Kip). It has been experimentally shown that the tensile force has a linear relationship with the compressive strength of concrete. Studies show that this relationship is independent of the ratio of water to cement, the type of cement and the processing conditions and the effect of aggregate size is very small (Fig. 2.31). The concept behind this method is that the tensile force required to pull a metal disk, together with a layer of concrete, from the surface to which it is attached, is related to the compressive strength of the concrete. The pull out experiment is normally used for early diagnosis of strength problems. However, it can be used to evaluate the strength of concrete in existing structures. Pull out experimenting involves attaching a small piece of equipment to the exterior bolt, nut, screw, or fixing. Then pulled until

Figure 2.31 Concrete pull out experiment.

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the designated stress load level to determine how strong and secure the fixing is. Benefits of this method 1. Relatively easy to use. 2. If relationship to strength is established, the method can deliver robust experiment results. Disadvantages of this method 1. It involves crushing and damaging concrete. Pull off experiment The pull off experiment is based on the principle that the amount of tensile force required to apply to a metal disk (steel or aluminum) to disassemble the disk, along with the concrete surface layer, is correlated with the strength of the concrete. Although this experiment requires surface preparation to provide complete continuity, it is an easy and fast method. This experiment is done in two ways. In the first method, the metal disk attaches directly to the concrete surface, and in the second method, a partial coring (a core that is not separated from the concrete) is first performed, and then a metal disk with a special epoxy adhesive is attached to the core surface. The advantage of this method is the failure of the deep layers of concrete to correlate the compressive strength, and the experiment results are influenced by the type of aggregate, the thickness, and the size of the disk. Indirect tensile strength experiment (Brazilian test) In general, concrete has less tensile strength than compressive strength. Because of this, reinforcement plays an important role in the tensile strength of structural members. In this method, a diagonal compressive force is applied at a specified speed along the length of the cylindrical concrete specimen to cause a break. This loading gives rise to tensile stresses at a surface under relatively high load and compressive stresses. Tensile failure occurs sooner than compressive failure because the load levels are triaxial. As a result, they withstand much greater compressive stresses than the uniaxial compressive strength test. Bending experiment to calculate tensile strength of concrete This experiment calculates the bending strength of concrete using a simple beam under loading. In fact, we can indirectly obtain the tensile strength of concrete by this test (Fig. 2.32). After the specimen is placed in the device, it usually first enters between 2% and 6% of the calculated final load. Then the load increases over time to reach the fracture boundary sample and eventually break. The tensile strength of the concrete is calculated by measuring the tensile stress of the concrete.

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Figure 2.32 Bending experiment to calculate tensile strength of concrete.

Figure 2.33 Rebound (Schmidt) hammer.

Nondestructive experimenting methods Rebound (Schmidt) hammer The experiment was invented some 70 years ago by a Swiss engineer, Mr. Schmidt, and is based on the force returning to the surface. The Schmidt hammer has a steel rod that comes in contact with the concrete surface. There is a weight inside the hammer that damages the steel rod with a certain amount of energy, and after the impact, the weight opens, while the horn attached to the weight shows the return value. In fact, the return number is the weight return interval in which the results are reported and linked by the calibration curve to the compressive strength of the concrete. The surface of the specimen that lies beneath the hammer bar should be perfectly flat and also the stiffness of the surface depends on the direction of the hammer (Fig. 2.33). According to the International Society of Rock Mechanics, it is best to place the hammer in one of three upright, horizontal, or downward

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positions. The methods based on the rebound principle consist of measuring the rebound of a spring-driven hammer mass after its impact with concrete. Rebound hammer is used to evaluate the surface stiffness. However, within limits, empirical correlations have been established between strength properties and the rebound number. In this method, pressure strength of concrete is experimented by through percussion hammer or reflective hammer using Schmidt hammer according to 85-ASTM C085. Results from experiments are estimation of reflected value of hardened concrete using steel hammer with springing force that is recorded in a table with average value of pressure strength with hits using Schmidt hammer. Therefore, regarding that maximum and minimum tolerance recorded for the results, coring experiments must be carried out to carefully examine pressure strength of concrete in seismic rehabilitation process. This experiment cannot be used for acceptance or nonacceptance of concrete since results depend on the mass and vibration. Tips that must be taken into consideration when carrying out this experiment: 1. This experiment is an estimation of return value of hardened concrete using a metal hammer with springing force. 2. This experiment can be used to determine uniformity of concrete in one place. This experiment can also be carried out to determine weak or damaged parts of structure, as well as the process of increasing the strength of concrete. 3. To estimate the strength of concrete, it is necessary to obtain the relationship between concrete strength and reflection number. This relationship will vary for each concrete mixing plan. To estimate the strength during construction, the strength of cubic samples in the laboratory should be determined and used to obtain the relationship. To estimate the concrete, the above relationship should be determined based on the determination of the strength of the samples obtained from the structure. (ACI-228R, methods to determine strength of concrete in place.) 4. For a specific mixing scheme, the reflection number is influenced by various factors such as surface moisture of the concrete, the method of obtaining the sample surface and the depth of carbonation of the concrete. These factors have to be reflected in the relation that is obtained to estimate the strength and the interpretation of the results of its effect. 5. According to the estimation of this experiment, it cannot determine the acceptance or nonacceptance of concrete.

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6. Based on the requirements of ASTM-C805 and Journal 72, as well as the 283rd Building and Housing Research Center, the results of this method are limited only to the quality of the surface layer of concrete (depth about 30 mm) and to determine the actual pressure strength of the concrete by breaking experiment (compressive strength jack). In addition, this device is used to compare concrete with a mixing ratio and a uniform moisture content. An example of Schmidt hammer experiment results is presented below. Schmidt hammers are suitable for concrete structures with a strength of 14009950 psi. Benefits of this method 1. It is easy to use for most field applications. 2. The experiment can be used to study the uniformity of concrete. Disadvantages of this method 1. The method is very subjective. 2. Surface condition, presence of rebar, presence of subsurface voids can affect the experiment results on-site evaluation of concrete strength— rebound hammer. Ultrasonic pulse velocity Ultrasonic experimenting, also known as ultrasonic pulse wave velocity, is based on determining the velocity of ultrasonic pulses passing through objects. Based on the method of placing generators in this experiment in three methods of direct, semidirect, and surface transmission it is possible that the most suitable situation is for direct wave transmission. In this situation, because the waves pass through the concrete, it is more accurate than other modes (Fig. 2.34).

Figure 2.34 Ultrasonic pulse velocity on concrete components.

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Based on the results of ultrasonic speed and compressive strength of standard specimens, a calibrated curve is prepared. Pulse penetration rate is different in different materials. For example, pulse penetration rate in steel is about twice that of concrete, so it is best to measure pulse velocity in nonreinforced areas. The moisture content has a great impact on the estimation of compressive strength by ultrasonic experimenting. Therefore, if calibration is performed on wet cubic specimens, the structural strength will be lower than the actual value. The influence of the type of aggregate on the calibration curve is also important in this way. Ultrasonic pulse velocity (UPV) is an effective method for quality control of concrete materials and detecting damages in structural components. The UPV methods have been traditionally used for the quality control of materials, mostly homogeneous materials such as metals and welded connections. With the recent advancement in transducer technology, the experiment has been widely accepted in experimenting with concrete materials. The experimental procedure has been standardized as “Standard Experiment Method for Pulse Velocity through Concrete” (ASTM C 597, 2016). Time spent of ultrasonic waves reflects the internal condition of the experiment area. Benefits of this method 1. UPV can be used to detect other subsurface deficiencies. Disadvantages of this method 1. The method is affected by presence of rebar, voids, and cracks. 2. There is no enough results for assessing the reliability of the method in the field. 2.2.2.2.2.2.2 Evaluation of steel strength

Some destructive tests for steel material Bending test They produce many products using processes such as bending, folding, squeezing, and deep metal pulling. Of course, these processes take place in the plastic (permanent formation of metals) range. However, the purpose of this test is usually to obtain bending at the “elastic” stage and to prevent the material from entering the “plastic” area. In this experiment, a rod is inserted between the two jaws of the machine and hung from its center of gravity by a different weight (or applied by a hydraulic jack to its center of gravity). As a result of the force applied, the part bends, which is measured by a hand-held deflection. This is called the deformation or Δ. The purpose of the experiment is to find the elastic modulus (Fig. 2.35). Tension test One of the destructive tests is the mechanical properties of solids. In this test the specimen is subjected to increased tensile strength

Seismic rehabilitation steps and practical methods in seismic rehabilitation of existing buildings 105

Figure 2.35 Bending test for steel components.

Figure 2.36 Tension test for rebar and steel material.

to break. Loading is performed mechanically or hydraulically. The loading system is usually equipped with a stressstrain register. This test is performed to obtain material specifications for designing or adapting specifications to specific user requirements so it can be a quantitative or qualitative test. Usually the results of this test are presented in the form of engineering stressstrain graphs (Fig. 2.36). Charpy impact test This test is one of the standard methods to determine the fracture energy of metal materials. In this test, using crushed specimens create three-dimensional stress conditions in the specimen and limit plastic deformation capability (Fig. 2.37). In this test, the amount of energy absorbed by the sample when fractured is obtained from the difference between the primary and secondary pendulum height. This amount of energy is a measure of the toughness of the material. The test apparatus consists of a graduated pendulum that

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Figure 2.37 Charpy impact test of steel material.

moves with the specimen as it moves and the height difference of the energy absorbed by the specimen, which is usually defined as the energy per unit area. This energy can also be calculated from the difference between the initial and final angle of the pendulum. Stiffness measurement Rockwell stiffness The most common hard test in the United States. The reason for this is the general acceptance of the test, its speed, inability to detect errors, the ability to detect small changes in hardened steel, and the small size of the recesses. Therefore heat treatment components can be tested without damage. In this experiment, the depth of trenches under constant load is used as a measure of stiffness. At first a subweight of 10 kg (22 lbs.) is entered. This minimizes the need for surface preparation, and the tendency to create troughs is automatically recorded in terms of conventional hard numbers on a calibrated plate scale (Fig. 2.38). Brinell stiffness It is the first standardized test accepted in 1900 presented by C. A. Brinell. In this test, the metal surface is formed by a 10 mm (0.4 in.) diameter steel bullet with a force of 3000 kg (6614 lbs.). The force applied by the punch is reduced to 500 kg (1102 lbs.) for soft metals to avoid the deepening of the impact of a deep recess and for very hard metals a tungsten carbide bullet is used. After the incision, its diameter is measured by a microscope. To obtain the exact diameter of the recesses, two diameters perpendicular to each other must be measured and averaged. The surface to be tested should be smooth and clean. Vickers stiffness A square-based pyramid is used as a puncture. The angle between the sides of the pyramid is 136 degrees. The reason for choosing this angle is due to the ratio of the diameter of the bullet to bullet diameter in the Brinell test (Fig. 2.39).

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Figure 2.38 Rockwell stiffness test for steel material.

Figure 2.39 Vickers stiffness for steel material.

The d/d ratio in the Brinell experiments ranges between 0.25 and 0.5. The d 5 0/375 D ratio is used for the Vickers test. So to make such a ratio, the angle of the cone must be 136 degrees. So when the normal value is obtained for the Brinell test, DPH and BHN are approximately equal. Because of the shape of the Vickers test puncture, it is also called the diamond pyramid stiffness test. Nondestructive testing (NDT) for steel material Nondestructive inspection methods can detect faults that occur from the beginning of manufacture to the manufacturing stage and then into the use of structural steel parts without damaging or destroying the test piece. Nondestructive testing can be performed on a component that is in use in one structure or one product, preventing potential defects and spreading the hazards and effects of those defects to other structures or components (Table 2.7). Common nondestructive testing methods • VT or visual test. • Inspection with LPT or liquid penetrant test.

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Table 2.7 Defects detectable with nondestructive testing. Defects caused Defects caused by Defects caused by the by raw materials assembly of parts manufacturing method

• Separation impuritySlag inclusions • Gas porosities • Contractile pores

• • • • •

• Cracks caused by excessive stress • Defects caused by excessive welding • Incorrect assembly • Parts left over

• • • • •

Shape Powder metallurgy Welding Heat treatment Machining

Functional defects

• Thermal instability Creep • Wear • Stress corrosion • Corrosion • Fatigue

Inspection with MT or magnetic particle test. RT or radiographic test. Eddy current test ET or eddy current test. Ultrasonic UT or ultrasonic test inspection. Inspection by AET or acoustic emission test.

Nondestructive testing steps • Step one: Using a physical property of the object and the test environment. • Step two: Change in the above property due to a fault. • Step three: Detect the change made with the help of a suitable detector. • Step four: Transform the revealed change in a way that can be interpreted. • Step five: Interpret the results. Acoustic emission test When a steel component is under stress, defects in it cause high-frequency sound waves. These waves are propagated in the matter and can be picked up by specific sensors, and by analyzing these waves they can determine the type, position, and severity of the waves. Acoustic emission testing is a new method of nondestructive testing. This method can be used to detect and position different defects in load-bearing structures and their components. Rapid discharge of energy from a centralized source inside the body causes transient elastic waves to propagate in the material. This phenomenon is called acoustic emission. Depending on the propagation of the waves from the source to the surface of the material, they can be recorded by sensors, thus providing information on the existence and position of the source of the radiation. These waves can have frequencies up to several MHz. Ultrasonic sensors in the range of 20 kHz to 1 MHz are used to hear material noise and breakdown of structures, and the common frequencies in this method range from 300 to 150 kHz. Depending on the type of application, the devices used can range from small portable to a large ten channels. A

Seismic rehabilitation steps and practical methods in seismic rehabilitation of existing buildings 109

single sensor, along with the associated tools for obtaining and measuring emission acoustic signals, allows the formation of an emission acoustic channel. The multichannel system is used for purposes such as locating resources or testing areas that are too large for a single sensor. Components for all devices to receive the signal include sensors, preamplifiers, filters, and amplifiers. Ophthalmic exam This is the most basic and usually the simplest method of quality control testing and equipment monitoring. In this way, the quality control engineer should inspect the items visually. Sometimes, though, cameras are used that send images to the computer and detect flaws. Radiographic examination Radiographic testing refers to the use of gamma and X-rays, which can penetrate many materials, to detect materials and detect defects in products. In this way, X-rays or radioactive radiation are directed to the fragment and then reflected onto the film after passing through the fragment. The thickness and interior features make the film appear darker or brighter. Magnetic particle test In this method, the iron particles are cast onto a material with a magnet and the magnetic field is induced. If there is a scratch or a crack on the surface or near the surface, the magnetic poles will form at the fault position or the magnetic field in that area will be distorted. These magnetic poles attract iron particles. As a result, the defect can be detected by the accumulation of iron particles. Ultrasound test In this method, high-frequency, low-amplitude ultrasound is sent into the segment. These waves are reflected after each break, and some of the waves go to the sensor and receive the sensor. The amplitude and timing of these waves can be attributed to the characteristics of this disruption. Applications of this method include measuring the thickness and detecting defects in components. Penetrant testing In this method, the surface of the piece is coated with a visible or fluorescent colored liquid. After a while, this fluid penetrates into the slits and surface cavities of the piece. Subsequently, the liquid is removed from the surface of the body and the appearance of the coating is sprayed onto the surface. The difference between the penetrating liquid and the appearance of the liquid makes it easy to see surface defects. This test is used to show defects that have surface access and can be applied to most materials of any gender, while the surface roughness of the test should be adequate. In this method, the surface must first be cleaned of grease and contamination, then the penetrant is sprayed on the surface and waited for at least 5 minutes for the penetrant to penetrate the

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defect. Then the surface is cleaned, and the appearance material is sprayed onto the surface, which is usually white. If there is a defect on the surface, its effect on the surface is determined Electromagnetic test In this method, an eddy current is induced by a variable magnetic field in a conductive material, and this current is measured. Discontinuities such as cracks in the material interrupt this process and thereby detect such defects. In addition, different materials have different conductivity of electrical conductors. Therefore some materials can be classified in this way. Thermography test One of these methods of monitoring and forecasting defects in mechanical and electrical machinery is the use of thermal analysis because the performance of each device is always associated with heat dissipation and usually any mechanical and electrical defects in equipment increase or decrease with temperature. The heat emitted from the outer surface of the body is released in the form of infrared radiation that is not visible to the human eye. But this radiation can be seen through thermography cameras, which are the most advanced and most complete thermal analysis equipment. Thermal analysis can be used to detect defects such as inadequate electrical connections, loose parts, and equipment, metallurgical changes, overload, and cooling. 2.2.2.2.2.2.3 Destructive tests on masonry materials

Mortar quality control in brick infill wall with destructive experimenting Mortar shear capacity experiment for measuring the strength of the mortar is carried out to determine the shear capacity of the wall. In addition, the architectural layer is taken off to examine how the wall is applied and the position of the units, the thickness of the horizontal and vertical sections, and the presence of mortar in the vertical connections, the existence of units for internal and external ridge connections. To determine shear strength in existing buildings in which infill frames are considered a part of the seismic system. According to the seismic rehabilitation instructions for the existing buildings, first by the removal of adjacent bricks, the sides of a brick in the outer ridge of the wall are emptied and the dimensions are measured [2,3] (Fig. 2.40).

Figure 2.40 Shear strength capacity of mortar material between brick of wall.

Seismic rehabilitation steps and practical methods in seismic rehabilitation of existing buildings 111

Then, by applying horizontal force using a jack, shear force necessary at the connection of brick to mortar until rupture of brick and mortar is measured. The results of these experiments are presented in a table for each mortar shear. Shear capacity of mortar is calculated through the following equation. For unreinforced masonry material, shear expected strength capacity vme calculated by (Fig. 2.41):
 0:75 0:75vte 1 PACEn vme 5 ; (2.1) 1:5 vtest 2 σD1L : (2.2) vto 5 Ab PCE, expected vertical force on wall

σD1L, vertical stress caused by gravity loads at the test site

An, cross section of wall

Ab, total area of up and down mortar at test position vte, average vto , 100 psi - if the masonry vtest, experimental load during the wall is a layer. Coefficient 0.75 should first displacement of the unit not apply to the formula.

Figure 2.41 Mortar shear strength capacity experiments steps.

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Mortar shear strength Vto must be determined according to experiments in a way that 80% of experiment values of Vto do not surpasses it. The walls with a mortar shear strength of less than 27 psi do not have the minimum quality conditions for the mortar, and they are vulnerable to shear strength. It should be explained that the calculation of average gravity tension and, consequently, shear strength of the mortar in the experiment reports should be corrected and presented in the form of corrective results of the mortar shear capacity experiments. In a table prepared by service and digging expert technicians to determine shear strength of mortar, if rupture occurs at support during the experiment, a replacement experiment must be carried out in another place. Therefore it is better for plan experts to determine places and a number of experiments 1.5 times higher than the actual number on the plan and experiment agenda. If vertical seams between the blocks not filled with masonry mortar, in-plane shear strength and strength to bending out from the wall, 50% of the calculated values of the wall to be complete. Unless these joints are filled with new and properly sealed mortar. Brick compressive strength test The purpose of the experiment is to calculate the amount of pressure that the desired brick can withstand (Fig. 2.42). Required supplies include: concrete jack crusher, ruler or caliper, its device, general laboratory equipment. Test description: We must first remove a sample of the brick by digging. Then place the specimen in the special apparatus. Finally, according to the force shown by the apparatus, we measure the compressive strength of the brick as follow: σ5

F : A

Figure 2.42 Brick compressive strength test.

(2.3)

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By default compressive strength is considered 60 kg/cm2 (900 psi) for good brick conditions, 40 kg/cm2 (600 psi) for medium brick conditions, and 30 kg/cm2 (300 psi) for weak brick conditions [2,4]. 2.2.2.2.2.2.4 Experiments needed to determine site specifications To classify

the type of ground, ensure about the status of soil under foundation, and to complete the information, by digging a borehole in primary studies, the following items are prepared and provided for the seismic rehabilitation expert. • General geological survey of the region. • Determination of the type, thickness, and relative density of underground layer. • Determination of physical and mechanical properties of layers. • Provide authorized strength and technical advice. It is also necessary to collect the following information in relation to the foundation soil based on selective performance (Fig. 2.43). • For performance levels of collapse threshold and safety, we must determine the type, texture, relative congestion, and soil layer in effective foundation depth (the depth in which tensions resulting from foundation load in soil are equal to or less than 10% of foundation floor tension). • Depth and seasonal changes of underground water. • For rehabilitation, determining special weight (γ), tenacity (c), inner friction angle (ϕ), condensability features, shear module (G), and the Poisson coefficient (υ) of layers of soil is necessary. The following experiments must be considered for studying target building: 1. Grading and hydrometer experiments—ASTM D422. 2. Experiment for determining Atterberg limit—ASTM D4318.

Figure 2.43 Triaxial shear experiment.

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Experiment for determining humidity percentage—ASTM D2216. Experiment for determining special mass (Gs’)—ASTM D854. Direct shearing experiment—ASTM D3080. Strengthening experiment—ASTM D2435. Triaxial shear experiment—UUASTM D2850. Triaxial shear experiment—CUASTM D4767. Standard penetration experiment in machine boreholes and cone penetration experiment in hand boreholes according to ASTM D1586 standards. The results must be explained in terms of layers according to laboratory and field experiment results and expert’s opinion about soil under foundation in project premise (Tables 2.8 and 2.9).

2.2.2.2.3 How can engineer define the required number of experiments?

The required level of information that determines the number of experiments required in seismic rehabilitation projects is divided into three main categories: minimal level, usual level, and comprehensive level. We will continue to discuss each of the above categories. 2.2.2.2.3.1 Minimum level of information In this case, the information contained in the calculations manuals or executive plans is considered as the lower-bound strength of a component. To reach the expected specification of the material, we can multiply the bottom line specification by 1/1. Note: The specification for the soil in the calculations manuals and executive plans of the foundation is considered as the lowest level of information at the minimum level of information. 2.2.2.2.3.2 Usual level of Information When the analysis has to be done nonlinearly, the least the level of information collected is the standard level. In this case, the number of experiments with the approach of the existence of technical documents is divided into two categories: • Technical documents contain reports results from experimenting materials that can be used and additional experiments can be ignored. • In case technical reports of materials’ experiment reports are not available, at least one tensile experiment must be conducted for each type of structural components such as column, beam, brace, and strengthening components and pieces. In metal buildings and pressure strength experiments in concrete buildings must be conducted for column and

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Table 2.8 Borehole experiments related to foundation. Row Name Application

Standard

1

Impedance logging

ACI 228.2R-98

2

Cross hole sonic logging

3

Parallel seismic (PS)

4

Induction field (IF)

5

Gamma logging Borehole sonic (BHS)

6

7

•

Borehole radar (BHR)

Determining approximate twodimensional shape and sizes in deep foundation Determining depth and geometry of foundation, determining position of concrete with undesirable quality along the foundation Determining uniformity of quality, determining depth of protruding candles, determining depth of shallow foundation or candle cap, determining candle existence under cap, determining the depth of candle under cap, determining geometry and specifications of foundation materials Determining protruding candles, determining candle existence under candle cap, determining candle depth under cap, determining specifications of foundation materials Determining position of areas with low density along foundation depth Determining depth of protruding foundations, determining depth of shallow foundation or candle cap, determining candle existence under cap, determining geometry and foundation material specifications Applications are similar to borehole sonic method

ACI 228.2R-98 ASTM D4428

ACI228.2R-98

FHWA-RD 94 052

ACI 228. 2R-98 FHWA-RD-94 052

FHWA-RD-94 052

shear walls. In this case, connection components must be chosen from the ones common in the building. If the results are approximate, the results of the average experiments are used as the expected strength of the materials. Otherwise, more destructive and nondestructive experiments should be carried out.

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Table 2.9 Surface experiments related to foundation.

Row Name 1

2 3

4

5

6

•

•

Sonic echo (SE)

Application

Determining foundation depth, determining surface foundation depth, determining candle cap from and on the foundation, determining depth and integrity of deep protruding foundation, determining crack status Impulse response Applications are similar to sonic (IR) echo Spectral analysis Determining geometry of surface of surface foundations, determining waves (SASW) specifications of foundation material, thickness, and determining rate of shear wave of different layers of soil Surface ground Determining surface foundation penetrating or deep or surface foundation radar (GPR) cap, determining candle under cap, determining geometry of foundation and foundation material specification Ultra seismic Determining surface foundation (US) depth or bases leading to surface foundation or candle cap, determining depth of protruding candles, and determining geometry and dimensions of foundation Dynamic Determining type of foundation foundation response (DFR)

Standard ACI228.2R-98 ASTM E1875 ASTM D4945 ASTM D5882

ACI 228.2R-98 ASTM E1876 ACI 228.2R-98

FHWA-RD-94 052

FHWA-RD-94 052

FHWA-RD-94 052

In all evaluations, to determine the knowledge factor, soil layers should be determined by sampling and performing field and laboratory experiments. The minimum number of boreholes and experiments required to collect information at the standard level is as follows: In case there are technical documents containing results of studying site in a standard manner such as boreholes digging and determining

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the soil layers and preparing a valid geotechnical report, no additional experiments are required and the values in geotechnical report can be used. Note: If there are no technical documents or in case of defect and inaccuracies in the available report, digging at least up to one borehole to depth of load tension penetration is necessary and it is required to conduct common geotechnical experiments in this speculation depending on the type of soil. 2.2.2.2.3.3 Comprehensive level of information In cases where special rehabilitation and analysis target is determined nonlinearly, information must be collected at comprehensive level. In this situation, the numbers of experiments falls into two categories according to information in technical documents: 1. Technical documents contain experiment report results on available materials. At least two experiments can be conducted for each type of structural components such as beam, column, brace, and strengthening components and parts. In this case, connection components must be chosen from the connections repeatedly used in the structure. 2. In case technical documents related to material experiment reports are not available, at least three tensile experiments must be conducted on each floor for every type of structural components such as beam, column, brace, and strengthening parts and components in steel buildings. In concrete structures, experiments determining used concrete components in beams, columns, connections, and shear walls must be conducted. In this case, connection components must be chosen from the connections repeatedly used in the structure. Drilling of at least one borehole is required to the depth of tensile load penetration and it is necessary to perform common geotechnical experiments in this borehole regarding available soil type. The criteria for determining the minimum number of bores and experiments required at the level of comprehensive information are as follows: 1. If a geotechnical report containing the results of a site survey of the available soil is available, at least the drilling of a borehole and field experiments and laboratory experiments should be carried out in the project site. 2. If there is no valid technical evidence on the availability of site conditions, at the level of comprehensive information, at least four

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boreholes should be drilled to determine the diversity of soil layers in the horizontal and vertical directions. If the approximate results are the same, the average experiment results are used as the expected strength of the materials. Otherwise, more experiments should be carried out in a destructive and nondestructive manner. 1. If executing plan are available at the time of inspection, digging one sample of each connection and eventually comparison to the plans are necessary. In case of consistency with plans, additional digging is not necessary. Otherwise, digging is continued until comprehensive consistency is reached. 2. If executing plans are not available at the time of inspection, digging three samples of each connection and eventually comparison to each other is necessary. In case of consistency, additional digging is not required. Otherwise, digging is continued until comprehensive consistency is reached. In a quantitative assessment of the vulnerability of existing buildings, it is important to provide an analytical model that can provide relevant information about building behavior and its components. To determine the members’ position, the geometry of the construction, and configuration according to the presentation of the agenda, appropriate digging is carried out. To recognize and dedicate detailed specifications of mechanical features of materials to components, experiments on structural components are required. If there are reliable documents, the number of experiments can be decreased. 2.2.2.2.4 Preparing digging plans and agenda

Generally, agenda for experiments and digging includes two main parts, experiment tables and plans, which are used by the plan expert to prepare digging agenda. The expert separates experiment tables using symbols at the beginning of the report, and finally, marks them on the plan. Below, an example of these tables is provided [5] (Table 2.10). To carry out the experiments, the expert must be present at the site to make the necessary decisions if the position of the experiments changes. In the application examples section, the digging layout method and the planning experiments are presented as a practical example. Table 2.11 is a sample table.

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Table 2.10 Sign explanations and details. Sign explanations and details

F

Determining size of foundation and plan Bp Determining dimensions of base plate and connection specifications W Nondestructive experiment for welding Bo Determining array of screws in connections and tensile experiment D Determining components of connections and determining geometrical members in metal and concrete members, ceiling details, and specifications of floors Dm Determining specifications of connections of wall to ties, wall to wall, horizontal and vertical specifications of ties, connection of beam to ceiling, array of walls in the building V Uncovering for scan control and determining reinforcement specifications

C

Coring from concrete

Tr

Tensile experiment for foundation bar Tensile experiment for bar, beam, and column Mortar shear capacity experiment Nondestructive experiment of Schmidt hammer Nondestructive experiment of concrete ultrasonic

Tb,c M N1 N2

S

Rb

Scanning reinforcements (determining diameter, cover, and bars array) Beam tensile experiment

Rc

Column tensile experiment

Table 2.11 Sample of test codes define method. Experiment and Coding Material type digging position

D,S,W,N1

31896/2/1/1

Dm,S,V,Rb,Rc,W

31896/2/1/2

Steel and concrete Steel and concrete

Component type Row

Beam and column Beam and column

1 2

2.2.2.2.5 An example of agenda for experiments and digging, tips on digging and coring operations with algorithms

•

The position of the sampling from the rebar and the coring of the concrete in the columns is in one-third of the height of the column (between the two floors).

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•

•

•

•

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The position for sampling of the rebar and concrete coring in beams where it is possible to take samples from beam’s web, is one-fifth of beam span and in beams which is not possible to take samples from beam’s web, sampling is done in one-third of distance form beam to column span. In addition, it should be noted that the arrows used in the plans indicate the member’s site where the experiment is carried out and the exact position of the experiment on the member is determined by the above criteria. The above criteria should be observed in all cases where the exact position of the sampling is not mentioned in the previous reports. If there is no possibility to perform operations on the above site for any reason, a new position will be determined in coordination with the seismic rehabilitation expert. If there is a need for a new coring, the new operation must not be performed on the same component, and the new position must be determined in coordination and confirmation of seismic rehabilitation expert. For the final selection, the position of the samples must be ensured that the stirrups and connections are not cut off. Coring should also be carried out in such a way that the number of broken reinforcements, if any, is minimal.  It is necessary that in conducting various experiments of concrete, steel, tracking of reinforcement, identification, the principle is to conduct the experiments and determine necessary specifications in an appropriate way, as well as limiting structural damages to the building and minimizing financial issues.  Therefore, in all experiment sites, if possible and in coordination with the seismic rehabilitation expert, several experiments can be implemented simultaneously. For example, in places for conducting digging horizontal tie inside the building, digging ceiling and determining its specifications, and also determining metal and concrete beam to horizontal tie are applicable (Figs. 2.44 and 2.45).

2.2.2.2.5.1 Stages of digging, sampling • Prior to the operation, it must be ensured that the sampling site is accessible. The positions of the member in each structure, according to the experiment plans, as well as the position of operations on each member, are items that should be controlled in the first step.

Figure 2.44 Coring zone position.

Figure 2.45 Digging and experiments algorithm for vertical and horizontal ties.

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•

Before carrying out the digestive process, it is necessary to use a suitable instrument to detect the position of the longitudinal and transverse reinforcements by means of a reinforcement tracker. • Depending on the case, make sure that the corrosion-resistant device is installed (including adjusting the height of the platform, the strength of the platform, etc.). • It is necessary to ensure that the platform on which the machine is installed is fixed during the operation. In general, if it is not possible to use a reinforcement tracker, slightly cutting the surface of concrete is recommended, depending on the steps of the corrosion or sampling operations of the reinforcement as follows. An example of a repair method for digging in destructive experiments replacing damage rebar in sampling. It is better determining an appropriate position for coring regarding minimum cutting of reinforcement and obtaining core in case reinforcement is cut off, the above steps can also be used. • After coring, the space above and below core, each is scratched to a length of about 20 cm (8 in.) and a width of 810 cm (3.153.95 in.). The depth of this space should be emptied as large as the reinforcement (the thickness of the reinforcement cover) and the surrounding area. • Two bars are cut to a minimum of 70 times the diameter of the rebar, placed on both sides of the existing armature and connected to the existing rebar on each side and top and bottom by welding. The length of the weld line in each part is at least 15 cm (5.90 in.) (for rebar up to a maximum size of 32 mm), it is necessary to infiltrate the welding and fill the space between the two rebar. 2.2.2.2.5.2 Steps to sample the existing reinforcement • Position of longitudinal reinforcements is identified similar to coring operation. • The concrete on the armature is cut and emptied in a space of about 90 cm (35.43 in.) long and 810 cm (3.153.95 in.) wide. • 50 cm (19.7 in.) of longitudinal reinforcement is taken, and two bars with minimum size 0.7 are cut and installed on two sides of the existing reinforcement and welded to the existing bar. The welding line should be at least 15 cm (5.90 in.) (for bars with maximum size 32). Welding must fill in the gap between the two bars.

Seismic rehabilitation steps and practical methods in seismic rehabilitation of existing buildings 123

•

If the coring operations are performed and the reinforcement sample is taken on a common column, it is necessary to first perform coring and then the reinforcement sample is taken in the same place of the core. The restoration operation is the same as before.

2.2.2.2.5.3 Steps to filling digging place with concrete masses The general recommendations for how to use the materials and how to fix them are as follows. The more detailed recommendations depend on the type of product used and the items in the brochures of these products. Therefore, for the consumption of products, studying these catalogs is necessary. Located of core position of existing building • It is recommended to use ready-to-use grout in these positions since additives need mixing for the position. For such cases where their uses are limited, some executable conditions might be problematic (due to disorientation in mixing ratios). • Consumable grout must have a controlled exfoliation property (to compensate for the contraction of concrete and ensure the filling of the sample position). • Consumable grout should be prepared from reputable company products that have a specific production date and consumption and are kept in good condition. • Depending on the conditions of the experiment area, appropriate additional materials should be selected and used. • The amount of use and how to use the products should be according to the instructions provided by the manufacturer. • Consumable mortar must not have slurry form. Rather, it must be fluidity because inadequate performance causes the mortar to stick in the span core thus end of the space remain empty. • The experiment position should be jaggy so that new and old concrete can be well-integrated. • The position of core should be cleaned of existing dust and debris. • Care should be taken to remove parts of the concrete that are laced. • New and old reinforcements should be covered with suitable materials to prevent possible corrosion. • Before concreting, the concrete site must be water lined up. • After proper molding (depending on the case), the necessary grout must be injected through appropriate method inside the core position and it must ensure that the air inside is emptied through a hole, and the

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position is filled completely. If necessary, an appropriate injection device or any other suitable means for appropriate concrete placement at the sample site should be used. In cases where there is no possibility to pour concrete in core position and position of removing reinforcement cover, after the core position is filled, repairing mortar with high adhesion feature must be used. According to the operating instructions of the manufacturing companies, the thickness of the maximum layers should be observed and, if necessary, the concrete should be laid in the form of layers using appropriate adhesives.

2.2.2.2.5.4 Surface restoration cases (positions for removing reinforcement) • In these cases, ready-to-use mortars that have good adhesion properties should be used. • The desired area is first cleaned with brush and air pressure and then water lined up. Then, depending on the operating instructions of the selected mortar, the mortar is applied in layers to the place and, if necessary, the concrete adhesive is used under each layer. • Before the mortar is executed, the concrete parts of the surface of the member, which have been loose during damaging the concrete, have to be removed from the body of the target. • The thickness of the maximum layers should be observed according to the instructions of the manufacturers of the products. 2.2.2.2.5.5 Steel joist or section with I shape profile To carry out tensile experiment, after sampling, it is preferred that two parts of sampling position are reinforced with a plate with the same dimensions and double thickness of the sample (Fig. 2.46). Boost page width 5 sample width 1 2t In addition, welding must be performed in the appropriate width. Length of reinforcement page 5 Sample length 1 2t, Sample thickness 5 t • Welding • If t , 6 mm(0.25 in.), then a 5 t • If t . 6 mm(0.25 in.), then a 5 t 2 15 mm Note: Profile flanges are welded from two sides. Note: In all cases where the materials have been demolished for testing and digging, the material should be repaired immediately after the required removal of the material required. Repairing the brick wall after the mortar shear capacity experiment. First, it is required to remove the

Seismic rehabilitation steps and practical methods in seismic rehabilitation of existing buildings 125

Figure 2.46 Steel joist or section repair.

bricks with pen and hammer, then remove the desired bricks and clean the mortar inside the cavity so that there is no excess mortar inside it. To put new bricks, the mortar is placed on the floor of the cavity with same sickness of the first mortar and a row of bricks is placed and screed is placed in a way that two ends of screed are placed on old bricks and middle part of screed is on new bricks. The bricks should also be aligned, and the rest of the bricks should be installed in the same way. To fill the last seam between new bricks and preinstalled bricks, cement trowel tip or jointer are used and mortar is placed inside. After this step, depending on the case, rehabilitation of daubery or jointer of brick are continued.

2.3 Methods of determining the vulnerability of existing buildings 2.3.1 Rapid qualitative assessment of vulnerability The first step in determining the need for rehabilitation is to collect the visual inspection information from the structure in a checklist and provide the checklist to the expert team. The checklist must be completed by supervisor and finally, the need for rehabilitation is determined by expert group through reviewing the information. It has been tried to provide a checklist including general information of the structure, information required for determining earthquake force, structural information, gravitational strength system, strength system against lateral load, in fills and

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walls, nonstructural walls and blades or separators, force transmission path, separation joint, half floors, mass distribution, configuration, brace frame, diaphragms, nonstructural components, infill frames, separators, facade, shelter and canopy, chimneys made of building materials, ceiling systems, objects inside the building, mechanical and electrical equipment, lightening equipment, general circumstances of site, and general information on foundation. Consequently, the reader can fill in the checklist and determine qualitative vulnerability of the structure. This method is free from any analysis, and depends on the knowledge of the expert studying the building. Therefore it is recommended to have professionals and seasoned experts. This type of analysis is mostly used for buildings that do not have special design [5]. After completing the checklist, with a qualitative look at the existing building damages a qualitative conclusion can be made. It should be noted that this checklist is an example of a checklist, which, if the building is different, should be compiled by the expert team of the project.

Additional general specifications 1. Place 2. Design date 3. Construction date 4. Current use & Residential & Administrative & Commercial & Educational & Therapeutic & Other 5. Primary user & Residential & Administrative & Commercial & Educational & Therapeutic & Other 6. Building condition in global position & Northern & Southern & Eastern & Western 7. Position of the building toward adjacent buildings. . .. . .. . . & Four free sides & Three free sides & Two free sides & One free side 8. Are there architectural plans? & Yes & No & Defective 9. Are there structural designs available? & Yes & No & Defective 10. Is there a calculation manual available? & Yes & No & Defective

Seismic rehabilitation steps and practical methods in seismic rehabilitation of existing buildings 127

11. Are there any technical documents available? & Yes & No & Defective 12. Does the building have an elevator? & Yes & No & Defective 13. Dimensions of the building respectively. Length. . .. . .. . .. Width. . .. . . Height. . .. . . 14. Length-to-width ratio of plan & , 3 &53 & . 3 15. Is there a building near the building? & Yes & No 16. Damage effect on building performance & High & Medium & Low 17. The impact of building failure in city vulnerability: & High & Medium & Low 18. The distance between the building and the relief center: & High & Medium. & Low 19. The relief route is appropriate & Yes & No 20. The texture of the buildings and the status of the lines of water, gas, electricity and telephone . . . 21. Average number of visitors to the building 22. The ability of those present to save themselves and others: & Good & Moderate & Poor 23. Type and position of exists and emergency entrances and exists 24. The state of the adjacent northern, southern, eastern, western streets 25. Population density in the area & Low & Moderate & High 26. Are there safe areas inside or near the building? & Yes & No 27. Current building value 28. Age of the building Information needed for determining earthquake force 29. Schematic acceleration 30. Soil properties. . .. . .. . . 31. Main construction period. . .. . .. . .. . . 32. Building weight including dead and live loads. . .. . . Structural information and general specifications of structural materials 33. Type of structural materials & Concrete & Steel & Brick & Concrete block & Wood & Stone & Other

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34. Type of roofing materials & Concrete & Steel & Brick & Wood & Other 35. Specifications of the ceiling & Block Joist& arched vault & Wood & Other (Composite) 36. The thickness of the ceiling 37. The components are fixed to the outlet and corridor by the clam & Yes & No 38. The ceiling should be constructed with light materials and framed and attached to the frame or ties so that the impact of earthquake does not damage the adjacent walls & Sufficiently & Not sufficiently & Not applicable General specification of structural system 39. Is there corrosion in components of the structure? & Yes & No 40. Have any components been damaged? & Yes & No 41. Are any members of the structure removed? & Yes & No 42. Have any changes been made to the structural components? & Yes & No 43. Is the number of building floors added? & Yes & No 44. Is there rust, corrosion, or deterioration in the steel components of the lateral or gravity load system? & Yes & No & Need to know more & Invisible at this stage 45. Are there any cracks in the concrete components? &Yes, diametrical crack &Yes, borderline crack & No, without crack & not applicable & No need for further review & Inaccessible at this stage 46. Does the building have structural components shared with adjacent buildings? & Yes & No Gravity resistant system 47. Gravity resistant system & Flexural frame & Plain frame & Plain frame with load bearing wall & Other Lateral load strength system 48. Type of structural system Axial X: 49. Type of structural system Axial Y: Infill frames and walls 50. Is there a structural wall in the structure? & Yes & No 51. Medium thickness of infill frames 52. Mortar for infill frames & Cement sand & Lime cement mortar & Lime sand & Mud & Other

Seismic rehabilitation steps and practical methods in seismic rehabilitation of existing buildings 129

53. Infill mortar: It should not be easily scratched by a metallic object and not in any area. & Sufficient & Not sufficient & Not available 54. The minimum thickness-to-height ratio for unbraced walls, for structural reinforced walls 1/15 and unstructured unbraced walls should not be less than 1/10, 1/12, 1/15, respectively? & Sufficiently & Not sufficiently & Not applicable Nonstructural walls and blades (or separators) 55. The maximum permitted length of the nonstructural wall between the two ends is 40 times the thickness of the wall, or 6 m & Sufficient & Not sufficient & Not applicable 56. Maximum permissible height for nonstructural walls and blades from an adjacent floor level is 3.5 m & Sufficient & Not sufficient & Not applicable & Need further investigation 57. Infill materials & Brick & Applicable 58. Infill thickness & Cement sand & Lime cement mortar & Lime sand & Mud & Other & None 59. Is there cracks in infill? & Yes & No & Not applicable 60. Infill connection &Separated & Without inhibition & With inhibition & Unrecognizable &Other 61. Separating wall type Made of pressurized brick with soil and plaster finishing Made of cement block with soil and plaster finishing

& &

Made of brick with soil and plaster finishing Made of small plaster panels with plaster finishing

& &

62. Are there cracks in separators? & Yes & No & Not applicable 63. The position of the upper edges of the blades with a height lower than the height of the floor with steel tie or reinforced concrete or wooden connected to the structure of the building or the blades surrounding the tie. & Good & Medium & Bad & Not applicable Force transmission path 64. Vertical joints of all vertical components in lateral load-bearing systems must continue to extend along the foundation and should not be cut at higher levels. In the direction X & Exists & Doesn’t exist & None In the direction Y & Exists & Doesn’t exist & None

130

65. 66.

67. 68. 69. 70.

71. 72. 73.

74. 75. 76.

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Separation joint Separation joint must be at least 1% of height away from the adjacent building. & Sufficient & Not sufficient & Not applicable The number of ways in which the distance from adjacent buildings is not enough. & One way & Two way & Three items & Not applicable The dimensions of separation joint at the lowest level and the highest level of the building are: . . .. . .. . . and. . .. . .. . . Are separation joint separated from the installation site? & Yes & No Is there contact between buildings in separation joint? & Yes & No Half floors and landings Half-classes must be independently inhibited from the original structures, or they must be connected to the components of the lateral load-bearing system of the main structure. &Sufficient & Not sufficient & Unrecognizable & Not applicable Has the existence of stairs landing on the floors caused to building a short column with shear performance? & Yes & No Did shear cracks occur in the landing? & Yes & No Mass distribution Distribution of flooring and additional masses to the building in floors and roofs & Symmetrical (in two directions) & Symmetrical (in one direction) & Asymmetrical Note: An expert will answer this question by examining the boarding and joining of walls and possible changes. The position of heavy objects and facilities & Lower floors & Middle floors & Upper floors & Not applicable Distribution of mass in floors & Uniform & Almost uniform & Not uniform Effective mass in any class should not differ by more than 50% from its upper or lower levels & Sufficient & Not sufficient

Seismic rehabilitation steps and practical methods in seismic rehabilitation of existing buildings 131

77. 78. 79.

80.

81.

82. 83.

84.

85. 86.

Configuration The geometric symmetry of the building plan. & Good & Moderate & Bad The ratio of the projection in the plan to the dimensions of the building in the same direction: The ratio of the projection in the plan to the dimensions of the building in the same direction: & Less than or equal to one fourth & Greater than one fourth & Not applicable Projection length at building height and compliance with its criteria. . .? & Less than 1 m2 (1550 in.2) with respect to the criteria & Less than 1 m2 (1550 in.2) without complying with the criteria & No more than 1 m & Not applicable The maximum permitted length of cantilevers for balconies with three open side of 0.5 m (19.7 in.) and for balconies with two open sides of 1.5 m? & All permissible & Slightly over-authorized & Mostly over-authorized & No cantilevers For building, the dimensions of projection in building plan, without separation joint are limited to the following values: & Sufficient & Not Sufficient & Not applicable Geometry of the dimensions of the plan for the lateral load-bearing system in each floor should not differ by more than 30% from the dimensions of the upper or lower floor (except for the dome roof)? & Sufficient & Not sufficient & Not applicable The torsion at each floor: the distance between the center of mass and the stiffness center in each of the two orthogonal direction of the building should not be greater than 20% of the building’s length? &Sufficient & Not sufficient & Not applicable Diaphragms Diaphragm opening in braced frames: Adjacent braced frame diaphragms should be less than 25% of frame length. &Sufficient & Not sufficient & Not applicable Levels of opening should not be more than 50% of the total area of the diaphragm. &Sufficient & Not sufficient & Not applicable

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87. Ceiling diaphragm performance &Good & Moderate & Bad & Unrecognizable 88. Connection between diaphragm and beams & Good & Moderate & Bad & Unrecognizable Nonstructural components General information about nonstructural components 89. Are there nonstructural components in the building that affect the interaction of structural components with the function of the building? & Yes & No Facade 90. Stone blocks should be properly restrained on the outer wall & Restrained & Not restrained & Not applicable 91. Considering the criteria for connecting the facade and decorative components with the restraining the metal wires if the bricks were applied after the construction of the wall, or the installation of a skewer or other suitable barriers for stone & Good & Medium & Bad & Not applicable & Unrecognizable Parapet and canopy 92. The height of the shelter around the roofs and balconies from the floor, if the wall thickness is 10 or 20 cm (3.907.90 in.), should not exceed 50 and 70 cm (19.727.5 in.) respectively. & Sufficient & Not enough & Not applicable 93. In case the ratio of permissible height to shelter thickness is not observed, the status of shelter is & Appropriate & Not appropriate & Unrecognizable 94. In case canopies exist, are they installed properly? & Yes & No & Not applicable Chimneys made of masonry materials 95. Unreinforced chimneys: Chimneys with building materials and similar components shall not be more than 1.5 m above the roof: & Sufficient & Not sufficient & Not applicable 96. If the height of chimney is higher than permissible range, chimney inhibition status and fixed or rigid chimney on roof floor with metal vertical components or concrete reinforcement. . . & Suitable & Not suitable & Unrecognizable & Not applicable

Seismic rehabilitation steps and practical methods in seismic rehabilitation of existing buildings 133

97.

98. 99. 100.

101. 102.

103. 104. 105. 106. 107. 108. 109. 110. 111. 112. 113.

Objects inside the building Objects taller than 1/20 m tall, such as a closet, file, cabinet, with a height to width ratio of more than 3 must be restrained to their floor slabs or adjacent structural walls. . .. . .. . . & Done & Not done & Not applicable Mechanical and electrical equipment The principle of the building facilities’ not damaging the main structural system & Good & Average & Bad & Not applicable Hazardous substance equipment Yes & No & Not applicable Adjunctive equipment over 10 kg (22 lbs.) of weight attached to the ceiling or wall, or other supports that are more than 20 m (787.5 in.) above the floor, are restrained. Yes & No & Not applicable Is there a fire system or fire extinguisher in the building? Yes & No & Lighting equipment Is lighting equipment restrained to prevent falls during an earthquake? Yes & No & Not applicable General conditions of the site Earth slope & Flat & Slope & On slope (with embankment) (slope percentage 10%) Distance from fault (km) Groundwater level (m) Soil type & Rock & Hard & Moderate & Soft Earthquake history & Low & Moderate & High Landslide hazard & Low & Moderate & High Danger of pacification & Low & Moderate & High Alluvial layer thickness Is there a subsidence in the building? Ground floor subsidence (no structural subsidence) & Yes & No & Not applicable What is the depth of drilling if drilling around the building? & Drilling is not done & Drilling up to level of foundation & Drilling below and up to level of foundation What was the use of the land on which the building was built?

134

114. 115. 116. 117.

118. 119. 120. 121. 122.

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General conditions of foundation Foundation system? & Individual & Stripped & Wide & Other & Needs more examination Foundation material? & Reinforced concrete & Unreinforced concrete Foundations performance: Is there a sign of significant movement of the foundation such as subsidence or drift that affects the integrity or strength of the structure? & Yes & No Deterioration: Are there any signs of deterioration of the constituent components due to corrosion, sulfate attack, disintegration or corrosion of materials, or other reasons that affect the integrity or strength of the structure? & Yes & No & Need further review & Not necessary Foundations of internal columns: Foundations of internal columns have a burial depth of at least 1.2 m? & Sufficient & Not sufficient & Not applicable & Needs further investigation Steel columns: Columns that are part of the seismic system should be properly attached to the foundation. & Sufficient & Not sufficient & Not applicable & Needs further investigation To what extent have the necessary arrangements been made for the lack of surface differences in the foundations? & Sufficient & Not applicable & Needs further investigation What is the total level of foundations? & Sufficient & Inadequate & Need further investigation Are the foundations slope more than 15%? &Yes & No & Not applicable

2.3.1.1 Rapid qualification of vulnerability This type of evaluation is mostly conducted by local experts based on the primary conditions without any experiments or digging. Effective parameters in this evaluation include dimensions, existing plans, and existing qualitative status. Considering that the evaluation method in this section is through visiting, it cannot be a definite criterion for decision-making for seismic rehabilitation. Rapid qualitative evaluation is mostly used for prioritizing buildings for rehabilitation. However, this type of evaluation can be used as an important parameter in categorizing and furthering seismic rehabilitation activity. At a glance for building types, this method has 10 main parameters that are effective in determining the vulnerability of a building. The expert completes the following checklist provided with some modifications based on the issues contained in

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the Iranian code No. (360) [3] and code No. (376) [4]. It is advisable to classify Parameter A into four main categories of seismic hazard. At the end of this vulnerability assessment, based on the LR computational domain, the risk of vulnerability is classified into four categories, which are presented in the following tables for how to classify the required items (Table 2.12). Seismic zoning classification A in this way. Seismic classification is generally performed by reputable regulators in different countries and is offered to engineers for use. Although you may hear the terms “seismic zone” and “seismic hazard zone” used interchangeably, they really describe two slightly different things. A seismic zone is used to describe an area where earthquakes tend to focus. A seismic hazard zone describes an area with a particular level of hazard due to earthquakes. Typically, a high seismic hazard zone is nearest a seismic zone where there are more earthquakes, and a lower seismic hazard zone is farther away from a seismic zone [4] (Table 2.13). LR 5 0:45 3 ½L3 1 L4 1 L5 1 L6 1 L7 3 L1 3 L2 3 L8 3 L10 3 ð7:5A 2 1Þ # 100:

(2.4) Note: It should be noted that this evaluation is quite qualitative and can be expanded according to experts.

2.3.2 Comprehensive and detailed vulnerability assessment 2.3.2.1 Introducing effective parameters and operations A detailed or comprehensive assessment of the vulnerability of existing buildings is a quantitative and accurate assessment by numerical calculations using the results of the experiments described in the previous sections. In this evaluation, the seismic optimization engineer selects a method of analysis based on the conditions of the analysis and performs quantitative vulnerability calculations on the main structural and nonstructural components based on the rehabilitation target. Finally, at the end of the vulnerability assessment, the level of vulnerability of the building is determined. To begin this operation, the most important modeling parameters to evaluate the seismic vulnerability of existing buildings that should be considered in the modeling are in the following. In modeling, structural features of the components must be considered and analyzed. The needed parameters are [2,3,6]: • stiffness; • strength; and • ductility.

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Table 2.12 Rapid e. Row Item name

1

2

3 4

5

6

7 8

9

10

Parameters

0 # φ # 15 15 # φ # 30 30 # φ Soil type Type 1 Type 2 Type 3 Type 4 Foundation Suitable Unsuitable Masonry Wall Structural wall with vertical building and horizontal tie Structural wall with horizontal tie Structural wall with vertical tie Steel or Other lateral Moment frame 1 brace or concrete frame system shear wall building Moment frame Simple frame 1 brace or shear wall Simple moment frame Roof RC slab and steel deck system Block joist Arch roof Wood beam Protrusion In accordance with standard standards Out of standard Building plan Symmetrical Asymmetric Windows and opening area In accordance with standard standards Out of standard Number of floor One floor Two floors Three floors or more Construction quality Good Medium Bad

Land slope

Coefficient

1 1.1 1.2 1 1.05 1.1 1.15 5 20 15 25 35 15 25 30 35 5 15 20 25 0 10 0 10 1 1.2 1 1.1 1.2 1 1.2 1.3

Seismic rehabilitation steps and practical methods in seismic rehabilitation of existing buildings 137

Table 2.13 Quality vulnerability range for existing building. Vulnerability

LR

Low Middle High Maybe collapse

LR , 25% 25% # LR # 50% 50% # LR # 75% LR $ 75%

Table 2.14 Type of stiffness in components. K 5 AE K 5 GJ L (2.5) L (2.6)

K5

M θ

(2.7)

Tension or compression, Torsional stiffness of a Rotational stiffness the axial stiffness, where straight section where J where M is the A is the cross-sectional is the torsion constant applied moment and area, E the (tensile) for the section and G θ is the rotation. elastic modulus (or is the rigidity modulus Young’s modulus), and of the material. L is the length of the element. Note that in SI, these units yield K 5 (N-m/rad) for the special case of unconstrained uniaxial tension or compression, Young’s modulus can be thought of as a measure of the stiffness of a structure.

2.3.2.1.1 Stiffness

Strength to displacement is called stiffness. For a given force, the small deformation of the structure is equal to the great stiffness of that structure. In earthquake engineering, stiffness is intrinsically examined in the elastic and linear behavioral range. Based on the amount of stiffness and mass of the structure, time period value of the structure can be obtained. Therefore, if the mass of the structure is constant, the time period and stiffness will be inversely correlated. The stiffness of a cross-section depends on the cross-section dimensions, the length of the element and the modulus of elasticity of the materials used. The elastic modulus of a material is not the same as the stiffness of a component made from that material. Elastic modulus is a property of the constituent material; stiffness is a property of a structure or component of a structure, and hence it is dependent upon various physical dimensions that describe that component. That is, the modulus is an intensive property of the material; stiffness, on the other hand, is an extensive property of the solid body that is dependent on the material and its shape and boundary conditions. For example, see Table 2.14. Stiffness of the structural components must be determined either through linear or nonlinear method. Stiffness must be considered with

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Figure 2.47 Stiffness chart.

Figure 2.48 Stiffness in linear method.

regard to stiffness-centered, shear-centered, moment-centered effects of the components. Regarding the types of analysis methods mentioned in the first chapter, stiffness curve analysis method is introduced for linear method (static and dynamic) and nonlinear static method (Fig. 2.47). 2.3.2.1.1.1 Stiffness in linear method In the linear method, the effective stiffness of the member in the forcedeformation curve is the line that connects the source to the yield (Fig. 2.48). 2.3.2.1.1.2 Stiffness in nonlinear method In the nonlinear method, the forcedeformation curve is determined nonlinearly and based on the

Seismic rehabilitation steps and practical methods in seismic rehabilitation of existing buildings 139

Figure 2.49 Stiffness for nonlinear method.

results of the experiments. To accelerate analysis of B, the forcedeformation curve is simulated. However, with regard to the analysis method, suggested ideal curves can be used. Given that the examples in this book are based on nonlinear static analysis, then the discussion and documentation of this kind of analysis are explained. The required stiffness can be used as in Fig. 2.49, which shows the general forcedeformation ratio. Ke 5 according to linear method-Kp 5 maximum 0:10 Ke : Numerical values of a, b, c, and d are determined according to performance conditions and type of component behavior that are provided in seismic rehabilitation instructions. The use of this method has the following limitations: • The main rotational time of the structure is less than 0.250.375 this number depends on the soil type of the site [1]. • The change in the size of the floor plan is less than 40%. • The maximum lateral displacement in each floor and in each direction is less than 1.5 times the average deformation of that floor. • The mean difference of lateral displacement of each floor with upper or lower floors is less than 50%. • The structure has a lateral orthogonal load-bearing system. • The ratio of force to capacity in all members is less than 2. 2.3.2.1.2 Ductility

The ability to withstand ultraviolet deformations and energy dissipation without noticeable loss in strength is called ductility. The ductility of an

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element depends on various parameters such as the amount of shear force in the element, the amount of compressive load, the dimension fit to the steel sections (cross-section compression), the length of the reinforcement, the amount of transverse reinforcement, and so on. Ductility-μ 5

Δu : Δy

(2.8)

2.3.2.1.2.1 Structural component’s action control The behavior of structural members proportional to their internal effort and the behavioral curve (forcedeformation) are expressed and evaluated in two ways. 2.3.2.1.2.1.1 A: Controlled by deformation In this species, there are predominantly plastic deformations, but due to the plasticity of the member, the plastic formability is limited. Below is a sample of controlled behavior by deformation. The behavior is controlled by deformation under flexural action, and the plastic deformation is completely visible in it (Fig. 2.50). 1. Components with ductile behavior For the main members, if the ratio (e/g) . 2 it is said, the behavior of this member is controlled by deformation. At the same time as applying the force corresponding to the behavior deformation in the OA region, these members have linear elastic behavior. In the area of AB, there is a complete plastic behavior, or plastic behavior with the possibility of hardening, that is, with a minimum of force, more deformation is observed. In the BC region, the strength decreases sharply, that is, while the force is removed, small deformations are still occurring. Behavior in the CD region is plastic again, but it is smooth, that is, the force is slightly reduced, but deformations are high. In the DE region, maximum deformation is observed.

Figure 2.50 Components controlled by deformation.

Seismic rehabilitation steps and practical methods in seismic rehabilitation of existing buildings 141

2. Components with semiductile behavior The difference in behavior in these components is that, up to point C, the deformationforce curve behaves almost the same, but then the behavior appears a brittle or nonductile behavior or controlled behavior by force (Fig. 2.51). 2.3.2.1.2.1.2 B: Controlled by force In these components, there is predominantly no plastic deformation, and the member immediately enters the stage of strength drop after suffering severe forces. Components with a brittle or nonductile behavior In such species, the range of linear elastic behavior is greater than that of controlled members by deformation. Therefore, after passing through the OA region, the strength is sharply reduced and reaches zero. For example, short pillars in boundary element of concrete shear wall have this behavior. Infills in Fig. 2.52 have the behavior controlled by force.

Figure 2.51 Chart of components with semiductile behavior.

Figure 2.52 Chart of components with a brittle or nonductile behavior (slab behavior).

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Table 2.15 Control the efforts of the main components. Controlled by deformation Type of component

Controlled by force

Moment frame

Flexural moment Flexural moment —

Beam Column Connection

Shear Shear and axial force Shear

Wall Couple beams Columns bearing shear wall

— — Shearing and axial force

Shear walls

Flexural moment and shearing Flexural moment and shearing Flexural moment

2.3.2.1.3 Strength

The capacity to withstand the effort is called strength to the effort (Shear strength, bending strength, axial strength, etc.). Strength in an attempt depends on various parameters such as: dimensions of cross section, length of cross section, strength of materials used, length of reinforcement, and the amount of transverse reinforcement. The components’ strength is determined by how much their behavior is controllable. In any case, the strength and deformation of structural members of the building should be based on the magnitude of the earthquake load, including at least three cycles of full reciprocation to the design surface. The behavior of components in flexural frames can be represented as an example in Table 2.15. 2.3.2.1.3.1 Strength of the material in components The strength of the materials can be considered as the main parameter in determining the strength required for the members. The low-bound and anticipated strength of the materials is the most important parameter in determining the capacity of the members. Briefly: • Nominal or recorded strength in technical documents at the level of minimum information can be considered as a low-bound of material strength. • The expected strength of the material is equal to the average values of the experiments defined or the application of a coefficient according to the instruction in the low-bound of the strength. 2.3.2.1.3.2 Capacity of structural components Calculation of the structural components capacity for use in acceptance criteria according to

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seismic recovery instructions FEMA 356 is divided into two main categories: • Expected strength capacity of the components, which is calculated using the expected strength of the materials, is called QCE. This factor consideration for deformation-controlled actions. • The low-bound strength capacity of components, which is calculated using the lowest strength of material is called QCL. This factor consideration for force-controlled actions. 2.3.2.1.4 Knowledge factor

To determine the capacity of each of the structural and nonstructural components, we need to apply a knowledge factor. This coefficient is extracted from the collected information and Table 2.16. This coefficient called K in FEMA 356. In linear analyses in which information is at the lowest level, this coefficient is considered k 5 0.75. This coefficient in nonlinear analyses has effective level k 5 1 based on the collection of usual or comprehensive level information [2,3] (Fig. 2.53). In accordance with the requirements of the seismic rehabilitation instruction of the existing buildings FEMA 356, the main parameters for the evaluation of the level of information for a building are evaluated. • Configuration of the building. • Members and materials’ specifications. Table 2.16 Knowledge factor range. Rehabilitation objective Special (enhanced)

Information level Any analysis Knowledge factor

Desirable or lower

Comprehensive Usual Usual Minimum Any analysis Any analysis Any analysis linear analysis 1 0.75 1 0.75

Figure 2.53 Knowledge factor needed for analysis.

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2.3.2.1.5 Demand modifier factor (m) based on nonlinear behavior or performance level

To modify structural components’ behavior and match with nonlinear behavior, this coefficient is provided for different components in FEMA 356. This coefficient called m in FEMA 356. 2.3.2.1.6 Load distribution

2.3.2.1.6.1 Load combinations for linear analysis For combining lateral and gravitational loads, maximum and minimum effects of gravitational load QG must be calculated by [2,3]: Type 1-QG 5 1:1ðQD 1 QL 1 QS Þ;

(2.9)

Type 2-QG 5 0:9ðQD Þ;

(2.10)

where QD 5 dead load; QL 5 live load; and Qs 5 snow load. The efforts resulting from gravitational load (calculated using equations above) must be combined with efforts resulting from earthquake load. For this, reciprocating motion effective of earthquake has to be considered; therefore, (QE) (effort resulting from earthquake load) is taken into consideration once with a plus and once with a minus. 1. Design efforts in components whose behavior is controlled by deformation, are calculated by: QUD 5 QG 6 QE ;

(2.11)

where (QE) is the earthquake load. Design efforts in components whose behavior is controlled through force must be determined using one of the following methods: 1. Maximum effort that is introduced to component by the structure. 2. Maximum effort that can be made in the component considering nonlinear behavior of the structure. 3. Force-delivery reduction factor used in force controlled action. It is called J (Table 2.17). QUF 5 QG 6

QE : C1 C2 C3 J

(2.12)

2.3.2.1.6.2 Load combinations for nonlinear static analysis To stimulate earthquake force on structure, two lateral load distribution should be introduced on the structure.

Seismic rehabilitation steps and practical methods in seismic rehabilitation of existing buildings 145

Table 2.17 Force-delivery reduction factor. Seismic zoning Performance scope

Zone high and very high relative risk Zone with average relative risk Zone with low relative risk Zone with average and very high relative risk

Safety—collapsing threshold Safety—collapsing threshold Safety—collapsing threshold Uninterrupted service and use

J

2 1.5 1 1

Note: In the combinations mentioned above, for more accurate analyses and evaluation we can determine combinations with load through considering accidental torsion.

1. First distribution The first type of distribution, the lateral load must be calculated and introduced on the model through one of the methods below. • Distribution appropriate for lateral load distribution in linear static method This distribution is applicable to structures that structure mass participation in first analysis modal is at least 75% in the direction being evaluated. • Distribution proper for the form of vibration mold mode in the targeted direction. This type of distribution is applicable for structures when at least 75% of the structure mass participate in this mode. • Distribution appropriate for lateral forces resulted from spectral linear dynamic analysis. This lateral load distribution is applicable for structures in which the selective vibrational modes in analysis have 90% participation in structure mass analysis. This lateral load distribution is used for structures in which Ts . 1 s. 2. Second type of distribution • Uniform distribution type 2 is a type of distribution in which lateral load is calculated in relation to weight of each floor. • Variable distribution is a type of distribution in which lateral distribution is changed through a valid method in terms of nonlinear behavior of structure model in each step of load increase. The lateral load selected in the order above must be separately introduced to model in positive and negative directions, and the relation between base shear force and control point displacement must be recorded for each step of lateral force increase to achieve a variation of at least 1.5 times the target displacement.

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2.3.2.1.7 Acceptance criteria for structural components capacity

2.3.2.1.7.1 Acceptance criteria for linear methods • Components controlled by deformation In the main and noncore components that are controlled by deformation, the following criterion must be met. m:k:QCE , QUD : •

(2.13)

Components controlled by force In the main and noncore Components that are controlled by force, the following criteria must be met. k:QCL , QUF :

(2.14)

2.3.2.1.7.2 Acceptance criteria for nonlinear methods • Components controlled by deformation In the main and noncore components that are controlled by deformation, the deformations resulting from the nonlinear analysis should not be greater than the corresponding capacity of that component in the direction of expected deformation. • Components controlled by force In the main and noncore components that are controlled by force, design forces must be smaller than the minimum strength of components. Compliant with seismic rehabilitation guidelines—essential information for calculating structural capability (Table 2.18). 2.3.2.1.8 Controlling overturning effects

Overturning of the structure is caused due to the lateral forces. The various types of lateral forces acting are: (1) wind loads, (2) seismic loads, and (3) earthquake loads. In case of retaining walls, lateral force is the force exerted by soil on the retaining wall. The force acting on the retaining wall from the soil or backfill is termed as earth pressure. When structures are subjected to lateral forces such as wind force and seismic forces, they undergo deflection in the lateral direction and lateral sway is observed in one direction of the structure. This causes structure to experience overturning (Fig. 2.54). Tall structures experience large lateral forces due to their height. Therefore they are designed in such a way that the structure can counteract the effect of overturning. When the design analysis involves the

Seismic rehabilitation steps and practical methods in seismic rehabilitation of existing buildings 147

Table 2.18 Seismic rehabilitation guidelines—essential information for calculating structural capability. Analysis Parameter Controlled by Controlled by deformation force

Linear analysis

Strength of available material Available capacity Nonlinear Capacity of deformation analysis in existing components Load bearing capacity of existing components Deformation capacity in new components Load bearing capacity in new components Strength of new components Capacity in new status

Target strength with Minimum regard to stiffness strength k.QCL m.k.QCE k. deformation level — —

k.QCL

Deformation level

—

—

QCL

Target strength of materials QCE

Nominal strength of materials QCL

Figure 2.54 Controlling overturning effects.

consideration of overturning effect, the stability of the structure increases up to a greater extent. If the overturning of the structure is not controlled, then it can eventually lead to structural failure. To ensure safety of structure against effect of overturning, a factor of safety is provided during analysis of the structure. Factor of safety to avoid Pthe overturning effect is calculated using the below expression. Here, MR is P the total resisting moment about the bottom end of the structure, and M0 is the total overturning moment about the bottom end of the structure.

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Figure 2.55 Calculating F in controlling overturning effects.

Overturning effect generally is the behavior controlled by force [13] (Fig. 2.55). P n n X X MR MR 5 Wi di Mo 5 Fi hi : Fo 5 P (2.15) M0 i51 i51 In the first method, the overturning anchor in linear (static and dynamic) analysis is given in the following equation only for dead loads in the calculation of a stable anchor. MST .

MOT ; C1 C2 C3 J

(2.16)

where MOT 5 overturning anchor in a floor, MST 5 stable anchor resulted from dead loads, and J 5 load reduction coefficient. J is load reduction coefficient, and it is calculated through one of the two methods below [2] (Table 2.19).

Seismic rehabilitation steps and practical methods in seismic rehabilitation of existing buildings 149

Table 2.19 J reduction coefficient.

In areas with a high and very high relative risk In areas with moderate relative risk In areas with a low relative risk For immediate occupancy performance

J52 J 5 1.5 J51 J51

Table 2.20 Determining RQT according to performance level. Performance level

RQT

Collapse threshold Safety Uninterrupted use capability

10 8 4

Note: In linear method, in addition to dead loads, the tensile capacity of the structural members must also be included in the calculation of the stable anchor.

Figure 2.56 Controlling overturning effects.

In the first method, the overturning anchor in linear (static and dynamic) analysis according to the relation, in addition to the dead loads, stretching in the components of the structure is also included in the calculation of resistant anchor [2] (Table 2.20, Fig. 2.56). 0:9MST . •

MOT : C1 C2 C3 J

(2.17)

The calculation of the stable anchor arm must take into account the performance of the lateral structure of the structural bearing (Fig. 2.57).

2.3.2.1.8.1 Overturning criteria in nonlinear methods In the case of an overturn in the nonlinear analysis, the following parameters should be taken into account.

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Figure 2.57 Controlling overturning effects.

Figure 2.58 Soil and structure interaction.

• •

Reduction and absence of tensile strength of the vertical members of the lateral load-bearing structure as a result of uplift. In case of decrease or elimination of tensile strength in a vertical component in a floor of the building, other structural components must have the ability to transfer and redistribute loads and the resulted displacements.

2.3.2.1.9 Soil and structure interaction

In what cases, in the linear analysis, must the interaction of the soil and structure be controlled? (Fig. 2.58). In structures located on soft soil or near a fault, when increase in the fundamental period of the building causes changes in accelerations and displacements of the structure due to interaction with soil. In case the interaction of soil and structure is taken into account, the forces from the analysis must not be smaller than 0.75 without considered without interaction. 2.3.2.1.9.1 Analyzing interaction of soil and structure In soil and structure interaction, soil stiffness must be examined and analyzed quantitatively with explicit modeling (using spring) of the following parameters (Fig. 2.59): • calculating low strain shear modeling; • calculating rigidity of foundations; and • calculating stiffness of springs. Note: Soil and structure interaction will be discussed in more details later in “Evaluation of the foundation.”

Seismic rehabilitation steps and practical methods in seismic rehabilitation of existing buildings 151

Figure 2.59 Analyzing interaction of soil and structure.

2.3.2.1.10 Simultaneous impact of earthquake in orthogonal direction

The simultaneous effect is such that 100% of the forces and displacements in each direction along with the forces corresponding to 30% of the displacement of the earthquake occur along the perpendicular to the structure. This effective parameter must be considered in side columns and other components that are joined in the area where earthquake force is applied in two orthogonal directions. In the following buildings, force application is necessary: • buildings with irregular plan; and • buildings with one or more connection columns between two or more frames in different directions. In linear analyses, if the conditions above are met, the earthquake effect is considered in any direction with 30% earthquake effect perpendicularly. In nonlinear analyses (static nonlinear), the force is for displacement corresponding to 30% of target displacement in the corresponding direction (Fig. 2.60). 2.3.2.1.11 Effect of vertical component of earthquake

The effect of vertical component of earthquake on seismic evaluation of buildings should be considered in the following cases: • Cantilever components and parts of building. • Prefabricated building components. • The members and pieces of the building under study, whose 80% of their nominal capacity is used under gravitational loads. 2.3.2.1.12 Introducing the effects of Pdelta

•

Element under lateral force V has displacement Δ. This displacement causes off-ax for axial load P which adds anchor with PΔ size to initial anchor resulted from lateral force V 3 h On the other hand,

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Figure 2.60 Simultaneous impact of earthquake in orthogonal direction. (A) Buildings with one or more connection columns. (B) Buildings with irregular plan.

• • •

additional anchor PΔ causes an additional displacement in the element, which in turn has PΔ effect and adds a small additional anchor. This cycle continues until displacement gradually moves to toward zero [1,2]. P, gravitational load without coefficient; V, horizontal Shear of the floor; and Δ, relative lateral displacement of the flood (Figs. 2.61 and 2.62).

2.3.2.2 Introduction to analysis methods 2.3.2.2.1 Introduction of linear analysis methods

Structural analysis is considered linear in terms of linear engineering for its component, taking into account the simplified effects of PΔ in terms of engineering. This analysis is mainly suitable for short and regular structures, in which the response of the structure during the earthquake is most suitable for vibration in the first mode. 2.3.2.2.1.1 Linear static analysis To better understand this type of analysis, the explanations below are provided following the discussion in Chapter 1, Understanding the Basic Concepts in Seismic Rehabilitation: • Basic assumptions. • Determining the main fundamental period of the building. • Determining linear static base shear force. • Distribution of lateral force at altitude. • Application of gravitational and lateral load. • Application range. 2.3.2.2.1.1.1 Basic assumptions

1. The behavior of materials in this type of analysis is linear (the elastic region).

Seismic rehabilitation steps and practical methods in seismic rehabilitation of existing buildings 153

Figure 2.61 Pdelta simulation.

Figure 2.62 Pdelta simulation.

2. The earthquake force in this type of analysis is considered a constant number, which is introduced as a coefficient of the weight of the building to the structure. 3. The earthquake force with the maximum structural deformation is roughly the same with what is expected in the earthquake of the

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expected hazard level for evaluation. This deformation is in the range where the structure has linear behavior. 2.3.2.2.1.1.2 Major and unessential components

•

Major components for forces and deformations caused by combinations of earthquake force load with gravitational load must be quantitatively evaluated in terms of vulnerability. • Unessential components for forces and deformations caused by combinations of earthquake force load with gravitational load must be quantitatively evaluated in terms of vulnerability. • Only the stiffness and strength of the main components are considered in linear analysis. In case the sum of lateral stiffness of unessential members exceeds 25% of the whole lateral stiffness of the major components in the building, the following solutions must be taken for analysis: • A number of components of the structure should be considered as major members, as long as this ratio is at least 25%. • In case removing some unessential components from the main structure causes reduction in force or deformation in main components of the building, then these components must be added to the model. • Structural components are categorized into major and unessential components so that there is no change in regularity or irregularity of the structure. 2.3.2.2.1.1.3 Ratio of application for linear static analysis method

• • •

The DCR in the components is equal to the force-to-capacity ratio, which in linear static analysis is less than 2. If DCR in the components is equal to or smaller than 1, the evaluated structure has completely linear behavior and the use of the linear method has the least number of errors. If DCR even in one of the main components is more than 2, then all three following conditions must be met: 1. There must not be any disconnection in the lateral load system on the plane and out-plane. 2. Average ratio of shear force to shear capacity of components of each floor is lower than 25% of its upper and lower floors. DCR 5

n X i51

DCRi Vi =

n X i51

Vi ;

(2.18)

Seismic rehabilitation steps and practical methods in seismic rehabilitation of existing buildings 155

Figure 2.63 Diagram time period and spectral acceleration in linear analysis.

where n is the total number of members and Vi is the shear force in the member i of the target floor, assuming that the behavior of the structure is elastic. Note: In soft-diaphragm buildings, this ratio for each frame axis should be individually examined. • In buildings with less than 20 floors Ts , T , 3.5Ts [2,3]. • Changes in plan dimension in sequential floors should be 40% maximum. • Maximum lateral displacement in each floor and in each axis must be 1.5 times larger than average displacement in calculated floor. • Maximum average lateral displacement in each floor, except for domeroof is 50% different from upper and lower levels. • The structure has a lateral seismic system in both directions (Fig. 2.63). 2.3.2.2.1.1.4 How to determine the main fundamental period of structural oscillation

Elastic fundamental period Ti If we give a system an initial displacement of unit size and drop it to resize the unit and return to the original position, this time will include a complete round process. What is the fundamental period of the structure? • If a structure is subjected to lateral forces, the structure will have oscillations, which for these oscillations are also defined as the periodicity parameter similar to the mass and the spring and we denote it by T. • The period parameter of the structure is one of the most important dynamic properties of the structure that plays an essential role in estimating the earthquake force. • Since the period of the structure is inversely related to the Stiffness of the structure, then the period is less in brackets or shear walls that are harder than bending frames.

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The main fundamental period must be calculated through one the following methods: 1. Simple experimental methods that are based on the measurements in available buildings. Height is the main determinant of fundamental period—each object has its own fundamental period at which it will vibrate. The period is proportionate to the height of the building (Fig. 2.64). (Table 2.21). hn 5 HeightðmÞ above the base to the roof level [13] Ti 5 Ct hβn :

(2.19)

2. Analytical methods which are based on dynamic specifications of the structure. 3. Using analytical software programs that provide the main period of structure in two directions. For more information, the reader can use Chapter 3 of FEMA 356 and Chapter 12 of ASCE 7-10.

Figure 2.64 Initial qualitative classification of periodicity of buildings. Table 2.21 Classified Ct, β for calculation fundamental period. Steel bucklingSteel Concrete Steel restrained eccentrically momentmomentbraced frames braced frames resisting resisting frames frames

All other structural systems

Ct 0.028 β 0.8

0.02 0.75

0.016 0.9

0.03 0.75

0.03 0.75

Seismic rehabilitation steps and practical methods in seismic rehabilitation of existing buildings 157

Figure 2.65 Effective lateral stiffness parameter effect on Te calculation.

Effective fundamental period Te The effective periodicity of the structure (Te) is a coefficient of (Ti) in the ratio of the squared elastic stiffness to the effective structure. The stiffness coefficients are derived from the binary curve of force and the displacement of the target structure. In diagram A of Fig. 2.65, the behavioral model shows a positive stiffness after the yield point (α . 0), and in diagram B the behavioral curve shows a negative hardness stiffness after the yield point (α , 0) [2,3]. rffiffiffiffiffiffi Ki Te 5 Ti : (2.20) Ke Fig. 2.66 is presented to better understand the concept of relationship between performance level and effective stiffness of the structure. It should be noted that as the earthquake hazard increases, the periodicity of the structure also increases relative to that of diagram B. Spectral acceleration Sa Spectral acceleration Sa is approximately what is experienced by a building, as modeled by a particle on a massless vertical rod having the same natural period of vibration as the building [3,6] (Fig. 2.67). T fundamental period limited value T0 5 0:2 TS 5 • •

SD1 ; SDS

SD1 ; SDS

(2.21) (2.22)

Sa, design spectral response acceleration Sa is a function of structure fundamental period T. Usually four regions define four equations in regulations or standard.

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Figure 2.66 Effective lateral stiffness at the different performance levels.

Figure 2.67 Spectral acceleration Sa.

In accordance with the FEMA 356 Instruction on Seismic Rehabilitation Project in the area of vulnerability assessment, the estimation of strong earth movements due to earthquake hazard levels is achieved in two ways: • standard design spectrum; and • spectrum of site-specific design (Fig. 2.68). 2.3.2.2.1.1.5 How to determine seismic lateral load (V) for linear static analysis In the linear static analysis method, the lateral force-induced

earthquake (V) is calculated seismic lateral load by [2,3] (Fig. 2.69): V 5 C1 C2 C3 Cm Sa W :

(2.23)

In linear analysis seismic lateral load corresponds to the displacement of the target in nonlinear analysis. Coefficient of relate expected maximum inelastic displacements, C1 Modification factor to relate expected maximum inelastic displacements

Seismic rehabilitation steps and practical methods in seismic rehabilitation of existing buildings 159

Figure 2.68 Combined earthquake hazard curve and building capacity in spectral curve.

Figure 2.69 How to determine seismic lateral load (V).

Table 2.22 Parameters of C1 formula.

1 T The main period of structure 2 Ts Period shared between two stable acceleration area and stable speed in design spectral reflection

to displacements for nonelastic deformations of the building, which is calculated through one of the following methods [2,3] (Table 2.22). 1. First method: An approximate formula for all domains but it is recommended to use more for the following domain T , Ts: C1 5 1:0 1

Ts 2 T : 2Ts 2 0:2

(2.24)

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Table 2.23 Parameters of R formula.

1 2 3 4

Sa Cm Vy W

Spectral acceleration per effective main period of structure Effective mass coefficient in the first mode Effective yield strength Structure seismic weight

Figure 2.70 Diagram of calculating C1.

2. Second method: In this method is applicable in case the strength ratio R is determined as below when we can calculated Vy (Table 2.23, Fig. 2.70): T . Ts -C1 5 1:0 and T , 0:1-C1 5 1:5;   T , Ts -C1 5 1:0 1 ðR 2 1ÞTs =T =R-R 5

Sa Cm : Vy =W

(2.25)

Coefficient of the effect of reducing the stiffness and strength C2 C2, in linear analysis, the value of this parameter, which represents the coefficient of the effect of reducing the stiffness and strength of the structural components, is considered equal to 1 [2,3]. Coefficient of PΔ effect, C3 Effective parameters in PΔ effects [13]. • Ratio of forcedisplacement curve slope after surrender to effective stiffness ~ : • Main period of the building. • Strength ratio R. • Lateral forcedisplacement relation for each floor. • Frequency of earth vibration.

Seismic rehabilitation steps and practical methods in seismic rehabilitation of existing buildings 161

Table 2.24 Parameters of θ formula.

1 2 3 4

Pi Ts Vi hi

Dead and live constant load and 25% live movable load on a floor Relative deformation of floor stiffness center Total floor shear Floor height

Figure 2.71 Diagram of calculating C3.

•

Extreme earth vibration period (Table 2.24, Fig. 2.71). θ , 0:1-C3 5 1:0; θ . 0:1-C3 5 1 1 5 Stability coefficient: θ



Pi δi θi 5 Vi hi

θ 2 0:1 : T

(2.26)

 (2.27)

Changes in C3 in terms of period of the structure In case stability coefficient is calculated larger than 0.33, then the structure is instable and must be rehabilitated [2,3]. Coefficient of the parameter for effective mass factor, Cm (Table 2.25, Fig. 2.72). 2.3.2.2.1.1.6 Seismic force in vertical distribution method Lateral latitude force distribution: to evaluate structure vulnerability in floor level, basic shear force resulted from the formulae is distributed in floors of the building [13] (Tables 2.26 and 2.27, Figs. 2.73 and 2.74).

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Table 2.25 Parameter of Cm formula. Row Number Flexural, Braced steel frame with of floors concrete, or concurrent or steel frames nonconcurrent axes

Structure or shear wall

Other structural systems

1 2

1 0.8

1 1

1 or 2 1 3 or 0.9 more

1 0.9

Figure 2.72 How to calculate V in linear method. Table 2.26 Parameters in lateral earthquake force distribution in the building height.

Fi Lateral seismic force in level i Wx Weight of floor with including weight of the ceiling and part of live load and half of the walls and columns that below and above the ceiling hx Height of level with, height of ceiling level with from the ground floor Wi Number of floors from base level (ground floor)

Table 2.27 Calculate K.

K 5 0.5T 1 0.75 K

T # 0.5 1

T $ 2.5 2

0.5 , T , 2.5 By using interpolation

Note: Lateral force for each building must be distributed in terms of weight distribution on each floor and by considering accidental torsion.

Seismic rehabilitation steps and practical methods in seismic rehabilitation of existing buildings 163

Figure 2.73 Lateral force distribution.

Figure 2.74 Rebound (Schmidt) hammer.

Wx hkx Fx 5 P V; n Wi hki

(2.28)

J51

Wx hkx

n P

J51

Wi hki

5 Vertical

distribution factor :

(2.29)

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2.3.2.2.1.1.7 Torsion As a simple analogy, one can imagine a building swing

in an earthquake like a child swinging during a swing. If the swing ropes are the same size and shape and the child is comfortable sitting in the middle of the swing, the two corners will surely move evenly when swinging. Building swings are just as inverted as swing (see Fig. 2.75). The columns and walls of the building will have the twisting ropes and the floor of the building will have the twist. The multistory building is like a swing with a few seats [1,3]. Let us go back to the example of twist; if you sit in the corner of the swing the other corners of the swing will not swing evenly and so will twist. It can be found in buildings where the floor mass is not balanced and has more corners (such as warehouses and libraries). Under these conditions, the heavier part of the building makes a larger horizontal movement (Fig. 2.76). In other words, the floor of the building is rotary in addition to the horizontal. The torsional moment force is applied only in diaphragms of a semirigid or rigid type, and it is not necessary to calculate the torsion in buildings with a soft diaphragm (Fig. 2.77).

Figure 2.75 Pattern of torsion due to inadequate distribution of floors.

Figure 2.76 Pattern of torsion due to inappropriate mass distribution.

Seismic rehabilitation steps and practical methods in seismic rehabilitation of existing buildings 165

Figure 2.77 Torsion of structure.

Figure 2.78 Real torsion of structure. (A) Improper geometric shape. (B) Improper distribution of walls and structural components.

Real torsion The actual torsion anchor on each floor of the building is equal to the sum of the multiplication of the lateral forces of the upper floors in the horizontal distance of the mass center of those floors in the direction of perpendicular to the load, relative to the stiffness center of the floor (Fig. 2.78). Accidental torsion Accidental torsion is caused by the following reasons [13]: Mistake in calculating the center of mass and center of difficulty • occasional displacement of live load (superimposed load); • not considering the torsion vibration of the earth; and • distinct strength of lateral load bearing members. Its value is calculated based on the existing from lateral load center relative to mass center 5% of building dimension perpendicular to the target direction.

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Table 2.28 Parameters to calculate torsional moment of floor i.

eij Horizontal distance of stiffness center in floor i and mass center level j Fj Lateral force in level j eaj Accidental eccentricity of level i which is considered to calculate probability of sudden changes in mass distribution, floor stiffness, and forces resulted from torsional index of an earthquake. This eccentricity must be considered in both directions and at least equal to 5% of the building dimension in level j and perpendicular to lateral force. Table 2.29 Torsional moment parameters.

dmax dmin η

Maximum horizontal displacement in one of the floors Horizontal displacement of mass center in the floor Ratio of torsional moment parameter

Torsional moment of floor i is calculated by (Table 2.28): Mi 5

n X ðeij 1 eaj ÞFj :

(2.30)

j51

• • •

• • •

Criteria for examining torsion in linear analyzes: If η $ 1.5, torsional moment must be taken into account in 3D model. If in all the floors η , 1.1 is obtained through complete torsional moment, accidental torsion can be ignored. If in one the floors η , 1.1, in linear analysis, force and displacements from accidental torsion in all floors must be multiplied by (Table 2.29, Fig. 2.79): h η i2 dmax A5 -η 5 (2.31) 1:2 dmass If the accidental torsion is less than 25% of the actual torsion, then the effect of the accidental torsion can be ignored. In case accidental torsion leads to increase in displacements more than 10%, it will be necessary to consider accidental torsion. Otherwise, it can be ignored. Effects of torsional moment must not be used to reduce forces and displacements of floors.

2.3.2.2.1.2 Linear dynamic analysis In this method, the forces and deformations caused by earthquake force are calculated using dynamic

Seismic rehabilitation steps and practical methods in seismic rehabilitation of existing buildings 167

Figure 2.79 Diagram of A and η.

equilibrium relations governing the linear elasticity mode. Basic assumptions: • The behavior of linear materials in structure can be calculated in the form of linear combination of different vibrational modes in the structure, which are separate from each other. • Period time structure vibrations in each mode is stable during earthquake. • In linear dynamic method, as in static method, structure response is multiplied in correction coefficient to estimate deformations. 2.3.2.2.1.2.1 Introduction to types of linear dynamic analysis method

1. Spectral method Vibration modes in this method must be chosen so that all the following conditions are met: • At least three first vibration modes are considered in each direction. • The total percentage of effective mass participation for each direction reaches at least 90%. • All modes that have period time more than 4% of second, must be considered. 2. Time history method • In this method, structural response is calculated through dynamic relations in short time steps influenced by the earth acceleration. • The structure response must be calculated at least with three Acceleration mapping.

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Figure 2.80 Chart for choosing analysis method according to T and drift.

•

In case seven or more Acceleration mapping are used for analysis, the mean effect must be considered for deformation and force control. 3. Estimating forces and deformations Values of forces and deformations from dynamic analysis must be multiplied in correct coefficient C1, C2, and C3. 4. Lateral force distribution in height and plan In linear dynamic method, lateral force is obtained in terms of mass acceleration and mass distribution in each floor by using dynamic analysis. Diaphragm of floors must be designed for sum of the following forces (Fig. 2.80). 2.3.2.2.1.2.2 The effect of concurrency of earthquake component in linear dynamic analysis This effect is introduced in the analysis in two methods:

1. Simultaneous effect of earthquake components is similar to linear static analysis.

Seismic rehabilitation steps and practical methods in seismic rehabilitation of existing buildings 169

Figure 2.81 The concept of nonlinear analysis.

2. The effect of components perpendicular to earthquake are introduced in two main directions on the structure model, and the obtained results are combined root sum square. 2.3.2.2.1.2.3 Application of linear dynamic analysis method In the case of the

two following conditions, a linear dynamic method can be used: • The DCR in the members is equal to the force-to-capacity ratio, which in L.S.P analysis is less than 2. • If DCR, even in one of the main members, is more than 2, all three of the following conditions must be met: 1. There must not be any disconnection in the lateral load system in plane and on the plane. 2. The ratio of shear force to shear capacity of members of each floor must be lower than 25% of its upper and lower floors. Note: For buildings with soft diaphragm, this ratio must be separately examined for each frame. 2.3.2.2.2 Nonlinear analysis

The analysis and evaluation of the structure of nonlinear behavior of components is called nonlinear analysis. This analysis is done with regard to nonlinear behavior of materials, cracking, and nonlinear geometric effects. In this analysis, the soft design spectrum is used, so the analysis is not sensitive to the changes in period time [2,3,6] (Fig. 2.81). 2.3.2.2.2.1 Nonlinear static analysis 2.3.2.2.2.1.1 Basic assumptions

Modeling assumptions • The structure should be modeled in 3D.

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The criteria for using the two-dimensional model: 1. The structure has a rigid diaphragm, provided that the target displacements are multiplied by coefficient. 2. In the modeling of soft-diaphragm structures, the effect of diaphragm deformation should be considered in terms of its Stiffness. 3. In soft-diaphragm structures in all classes, it is possible to analyze the frame in vertical lateral load-bearing systems separately with the assigning of the mass proportional to the load bearing level of the frames. • In nonlinear two-dimensional analysis, the calculation of the stiffness and strength of the components and members of the structure is considered as a three-dimensional one. • If the effect of the presence or absence of connections in the model results in 10% difference, the impact of the connections must be applied in the structural model. Nonlinear static analysis methods can be done in one of two ways: Complete way: • Main and noncore members are modeled. • Nonlinear behavior of members are carefully estimated. • Decreasing effects are included in the calculation. Simplified way: In this way, the following terms and conditions must be met: • Only the original members are modeled. • Force diagrams and nonlinear deformations of the main members are determined by the bilinear model. • Decreasing effects are not included in the calculations. • Deformation-controlled main members that are subject to the acceptance criteria should be monitored for efforts in terms of the performance level of rehabilitation of the building. If a small number of main members are not accepted by this criterion, these members can be considered noncore members and be eliminated from the model. Target displacement The roof’s mass center is the control point for the structure displacement for define the target displacement. Specify target displacement Target displacement for the structure is estimated by considering the nonlinear behavior of the structure. This number is calculated only for rigid diaphragm. δt 5 C0 C1 C2 C3 Sa

Te2 g: 4π2

(2.32)

Seismic rehabilitation steps and practical methods in seismic rehabilitation of existing buildings 171

Table 2.30 Coefficient value. Other building Shear buildingsa Any load pattern

Triangular load pattern

Uniform load pattern

Number of floors

0.1 1.2 1.3 1.4 1.5

1.0 1.15 1.2 1.2 1.2

1.0 1.2 1.2 1.3 1.3

1 2 3 5 10 or more

a

Buildings in which, for all stories, inter story drift decreases with increasing height.

Coefficient for relation between SDOF and MDOF system, C0 Correction coefficient for relation between spectral displacement of one-degree freedom system (SDOF) and roof displacement of multidegree freedom system (MDOF), which is equal to Table 2.30 [2,3]: Coefficient for displacement in C1 This coefficient is used to convert inelastic displacement to displacement calculated for linear elastic response (Fig. 2.82). • For Te , Ts, if the ratio of strength R is known, we can use the relation presented for the calculations in a linear way to calculate C1. • The value of C1 must not be smaller than 1 and larger than its value based on the second relation. Coefficient of decrease in hardness and strength due to nonearth behavior, C2 This coefficient applies the effects of strength and stiffness reduction in structural components on displacements due to their nonelastic behavior [2,3]. The value of this coefficient is calculated as in Table 2.31. In the table above, type 1 frames include instrument systems in which more than 30% of the lateral load is carried by members who have reduced stiffness and resistance during an earthquake. Coaxial braced frames and frames with semirigid joints, frames with slim braces designed only for traction, and masonry walls and unformed brick walls are type 1. For the other T values not provided in the table above, C2 is derived from the interpolation method (Table 2.32). Coefficient of PΔ effects, C3 C3 5 1:0 1

jαj½R-11:5 : Te

(2.33)

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Figure 2.82 Coefficient for displacement in C1. Te . Ts -C1 5 1:0: Table 2.31 Table for calculating value of C3. Structural performance level T , 0.1 sec

Immediate occupancy Life safety Collapse prevention

T $ TS

Framing type 1

Framing type 2

Framing type 1

Framing type 2

1.0 1.3 1.5

1.0 1.0 1.0

1.0 1.1 1.2

1.0 1.0 1.0

Table 2.32 Table for calculating value of C3.

α . 0 Structures that have positive stiffness after surrender α , 0 Structures that have negative stiffness after surrender

1 Calculated through equation

Value of C3 is not larger than calculated values in linear static analysis relation [2,3].

2.3.2.2.2.2 Nonlinear dynamic analysis In the nonlinear dynamic analysis method, as well as static nonlinear, the structure response is calculated and determined according to the nonlinear behavior of the material and the nonlinear geometric behavior of the structure by determining the target displacement. In this type of analysis, the response of the modeled structure under earthquake acceleration can be calculated numerically and for any time period.

Seismic rehabilitation steps and practical methods in seismic rehabilitation of existing buildings 173

2.3.2.2.2.2.1 Basic assumptions

• •

The stiffness and damping matrix can be changed from one step to the next. The length of each time step is constant.

2.3.2.2.2.3 Modeling components in software • Nonlinear behavior of all main and noncore members must be considered in modeling. • Reduction of effects must also be taken into account in behavioral model of members. For analysis, the following should be performed: 1. The earth acceleration must be determined. 2. In each direction, analysis must be done at least for three accelerometer. 3. The effect of earthquake force must be considered Orthogonal to the model. 4. Structural response for accelerometers must be determined. Structural response is calculated for the following situations: • At any rate less than 7 accelerations, the structure response should be considered equal to the maximum response. • At each rate of 7 accelerations or more, the response of the structure can be selected as the average response. 2.3.2.3 Chords and collectors in diaphragm Diaphragm itself is made up of different components. One of these components is collectors. Collectors’ task is to collect lateral forces from different parts of diaphragm and transfer these forces to different lateral resistant forces such as shear walls, flexural frames, or brace frame. Collectors and lateral resistant forces are on the same axis and transfer forces through axial performance in the form of tensile and compressing forces. Collectors are placed on two sides of lateral resistant components in the same direction and in parallel form [1]. Either collectors can be at the width of the lateral resistant element or wider than the lateral resistant element, in which case part of the lateral force is transmitted by the friction shear function. If the lateral resistant element extends throughout the width of the plan (parallel to the earthquake force), the transfer of force is performed in another way (Fig. 2.83). In this case, the force transfer is accomplished by directly connecting the ceiling diaphragm to the lateral resistant components, mainly through the friction shear function. In friction shear the lateral resistant element

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Figure 2.83 The concept of chord and collector in diaphragm.

and diaphragm might have cold connection (concreting takes place at two different times). In this situation, the connection is made using rebar’s friction shear half of which is in the diaphragm and the other half in the lateral resistant element and force is transformed. 2.3.2.3.1 Chord components

Another component of the diaphragm is the chord element. These components are perpendicular to the earthquake lateral force and are located on the edges of the diaphragm or on the ceilings of large openings. These components play a role similar to the boundary element in shear walls. Most of the flexural anchor inside the plate created by the diaphragm force is tolerated by these components. These components are designed based on tensile or compressive axial forces. To provide the flexural strength required in the diaphragm and to prevent reinforcement congestion in a small area of the diaphragm, the width of these components can be considered up to a quarter of a dimension parallel to the earthquake lateral force. Performance of diaphragm edge (chord) in bearing diaphragm flexural anchor 2.3.2.3.2 Distributer element

The distributor element is another part of the diaphragm. This part is needed when one of the lateral resistant components (such as shear walls) is cut off at the upper floors and is not extended to the lower floors or moved to another position in the plan. In this case, the ceiling diaphragm in this alignment has the task of collecting the force of the upper floor components and transferring them to other lower floor resistant components. Distributor is a longitudinal element in the length of cut-off lateral resistant element. Similar to collectors or chords, distributors are influenced by axial force that can be in the form of tension or compression (Fig. 2.84).

Seismic rehabilitation steps and practical methods in seismic rehabilitation of existing buildings 175

Figure 2.84 Distributer in diaphragm.

Distributor element in the diaphragm at the point of disconnection of the lateral load-bearing system at altitude. 2.3.2.3.3 Diaphragm analysis

The ceiling diaphragm must be designed with the influence of specific lateral loads and simultaneously analyzed and designed with the effect of gravity loads. For structural analysis under diaphragm lateral loads, it can be considered as a deep beam. The direction of this beam is perpendicular to the lateral forces. The depth of the beam is the same as the lateral plane of the lateral force and the supports of the beam are the lateral reinforcing frames (walls, flexural frames, and braced frames). Based on the lateral loads, this hypothetical beam can be analyzed and the shear and anchoring can be diagrams extracted, and the diaphragm can be designed based on the values obtained for the cutting and anchor. Shear force can be tolerated by all components of the diaphragm (at a point in the diaphragm parallel to the shear force). The flexural anchor can also be tolerated mainly by chord components. 2.3.2.3.4 Ceiling diaphragm design criteria

As mentioned in the preceding chapters, to tolerate bending anchor, as a simplified method, we can use up to one-fourth of hypothetical beam dimension (plan dimension in the direction of lateral force) in bending

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anchor tolerance. In the event of a plan dimension change (a change in the height of the hypothetical beam) or a pop-up in the plan, it is necessary to extend the fittings in the diaphragm to withstand bending as much as the inhibitory length in the adjacent section. Instead of using this simplified method, the finite element method can also be used to calculate the exact values of stresses in different parts of the roof and design different sections of the diaphragm accordingly. Note: Influenced by lateral forces in diaphragm and the resulted bending anchor, in parts of ceiling where concrete compression strength increases up to 0.2, it is necessary that similar to boundary element of shear wall and also concrete columns, longitudinal reinforcement of chord element are surrounded properly by latitudinal reinforcements. The same is true of the edges of openings of the diaphragm. Parts of the diaphragm of the ceilings are more sensitive and more forces are concentrated in them, therefore they need to be scrutinized more closely. Structures with irregular geometry in height which have a significant change in plan dimensions are of this type. In these cases, as the plan changes, the ceiling diaphragm undergoes significant forces due to the components of the upper floors. This force needs to be moved to the new components added to the plan in the lower floors. Another level that is influenced by this is the Podium level (Fig. 2.85). Podiums exist in buildings with basement floors, and because of the peripheral retaining walls attached to the structure, the basement level is higher than the foundation level. In these buildings below the base level, a function called Backstay effect occurs that causes a noticeable reverse shear in the diaphragm of the ceiling that needs to be scrutinized carefully (Fig. 2.86).

Figure 2.85 Podium level in structure.

Seismic rehabilitation steps and practical methods in seismic rehabilitation of existing buildings 177

Figure 2.86 Diaphragm inertial force. Table 2.33 Parameters for calculated seismic force for diaphragm.

Fpx Fi Wi Wx

Total diaphragm inertial force at level x Lateral load applied at floor level i Effective seismic weight W located on assigned to floor level i Effective seismic weight W located on assigned to floor level x

The diaphragms should be designed to incorporate the effect of the Fpx force parameter. These effects are obtained by [1] (Table 2.33): Fpx 5

n X i

Wx Fi P n Wi

(2.34)

i5x

Evaluation of diaphragm demands should be based on the likely distribution of horizontal inertia forces. For flexible diaphragms, such a distribution may be given by [2,3] (Table 2.34, Fig. 2.87): " 2 # 1:5Fd 2x f5 (2.35) 12 Ld Ld 2.3.2.3.5 Diaphragm ties

In the diaphragm, continuous tensile ties that connect the two edges opposite the diaphragm or beam should be used. The distance of the coils shall not be more than three times the length of the ties. The length of the ties is the distance between two consecutive points of its transmission

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Table 2.34 Diaphragm demand parameters.

fd Fd x Ld

Inertial load per foot Total inertial load on a flexible diaphragm Distance from the center line of flexible diaphragm Distance between lateral support points for diaphragm

Figure 2.87 Diagram of applied force and shear force.

Figure 2.88 Diaphragm cohesion ties.

force as other members of the lateral bearing, such as frame beams. In the case of diaphragm tie design, the axial load of the diaphragm ties design is the behavior of the force in floor design have the force-controlled function. Weight of the diaphragm part attached to tie beam use for calculated FP as W parameter. The weight parameter W considered in this formula is equal to the weight of the load bearing surface of the tensile ties [2,3] (Fig. 2.88): FP 5 0:4SSX W :

(2.36)

Seismic rehabilitation steps and practical methods in seismic rehabilitation of existing buildings 179

2.3.2.4 Structure wall and infill panels 2.3.2.4.1 Walls

In general, walls are shell components consisting of building materials or modern materials. These components that are enclosed with tie, steel, or concrete or nonreinforced frames are divided into three categories: structural walls, infill walls, and separating walls (nonstructural walls). 2.3.2.4.2 Structural wall

This is a wall designed to withstand vertical or lateral loads or both, and is one of the key components of building durability throughout its life. The complete evaluation of structural walls in the building materials section will be presented in full. 2.3.2.4.3 Infill walls

These walls are enclosed in steel and concrete frames and can withstand part of the earthquake force at the time of the earthquake due to strength and stiffness (Fig. 2.89). Fig. 2.90 shows the strength of a frame with or without a wall. As can be seen, the frames with the infill wall can be more resistant to the surface underneath the diagram than the simple frames 2.3.2.4.4 Separating wall (separators)

Separating walls are used to separate interior space of a building. The weight of these buildings are not usually calculated in structural calculations and their weight is tolerated by the components below. A thorough

Figure 2.89 Schematics of Wall and Infill wall. (A) Frame without infill wall. (B) Frame with infill wall. (C) Wall.

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Figure 2.90 Comparison of simple frame and frame behavior with infill wall.

Figure 2.91 Frame with infill test.

evaluation of the separation walls is presented in full in the building materials section. • Directly by the foundation. • Through the floor by the load bearing walls. 2.3.2.4.4.1 Analyzing behavior of infill frames Infill mentioned in this book are walls made of compressed brick materials, hollow concrete blocks, or hollow compressed bricks that partially or completely cover steel or concrete frame openings in a structure and surround beams and columns made in that frame. In this chapter, frames containing infill brick frames are discussed (Fig. 2.91). • The presence of a brick wall inside the frame practically prevents the frame from moving on its screen, thus part of the lateral force applied to the frame is transferred to the infill frame. Past observations, experiences, and extensive theoretical and laboratory research have shown

Seismic rehabilitation steps and practical methods in seismic rehabilitation of existing buildings 181

Figure 2.92 Capacity of infill wall for types of failure.

that the strength and stiffness of these frames are far more than bare frames (without infill). • The interaction of tie (frame) with wall (infill frame) in buildings increases strength and stiffness on one hand, and increases softness of the wall, thus improving building performance. These frames are called compound frames. • Boundary crack is along with stiffness decrease. As the force increases, walls start cracking along the pressure diameter and behavior of the wall changes to nonlinear. The diameter crack indicates the shear failure of the infill frame. As the force increases, the stress concentration in the corner of infill causes the material to break and a pulley hinge is formed in the beam or column near the corner (Fig. 2.92). General principle of seismic rehabilitation of infill frames in compound frames is determine how infill frames are placed in the frames. This mixture falls into two main categories: the first type is infill frames connected to the frame which function as infill frames with shear behavior and which usually need rehabilitation. The second type is infill frames that are not completely surrounded in the frame, therefore, have a more appropriate performance in steel structure. Also, each of these infill frames must be analyzed regarding the different placement-related behavior against displacement. 2.3.2.4.5 Out-of-plane strength

2.3.2.4.5.1 Force on wall post This is force-controlled behavior of wall connection in a direction out of the diaphragm plane.

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Table 2.35 Damping adjusted for site class α. Structural performance level Flexible diaphragm

Other diaphragm

Collapse prevention Life safety Immediate occupancy

0.3 0.4 0.6

0.9 1.2 1.8

Figure 2.93 Out-of-plane force on wall. Table 2.36 β parameter.

Structural performance level

β

Collapse prevention Life safety Immediate occupancy

0.3 0.4 0.6

Maximum distance of wall post 2.5 m. The weight parameter W used to calculate the applied force is the weight of the wall post area combine with wall [2,3] (Table 2.35). FP 5 α:Ssx W :

(2.37)

2.3.2.4.5.2 Force on the wall The wall components must be sufficiently strong to withstand the forces outside the wall plate. The weight used to calculate this force is equal to the weight of the wall per unit area [2,3] (Fig. 2.93, Table 2.36). FP 5 β:Ssx W :

(2.38)

2.3.2.4.6 Integration of building parts

2.3.2.4.6.1 Two parts of building All members of the building must work together to provide the proper path for earthquake forces to move from one component to another. Responses from earthquake forces discussed in this section are considered as force-controlled parameters.

Seismic rehabilitation steps and practical methods in seismic rehabilitation of existing buildings 183

Figure 2.94 Integration of building parts.

In multicomponent buildings, each part of the entire building must be closed by components with sufficient strength to withstand the horizontal force in any direction, unless the different parts of the building have a separate load-bearing system and have their own disconnect seams are separated. As it is seen in Fig. 2.94, buildings may have a common area between components. In this situation, horizontal force in designing the connection of two parts of the building have force-controlled behavior. The amount of this force is obtained through the following equation. Weight of the smaller part of the building used for calculating [2,3]. FP 5 0:133 SSX W :

(2.39)

2.3.2.4.6.2 Attachment to the adjoining components such as the parapet wall The behavior of the components in this situation is also force-controlled. Weight of the attached part to building use for calculated FP as W parameter. The weight intended for W is the weight of the smaller part of the building [2,3] (Fig. 2.95). FP 5 0:08 SSX W :

(2.40)

Note: If at least one end of the slider supports is incorporated, the length of the support should be sufficient to allow the expected relative displacement of the component to be supported. 2.3.2.4.6.3 Building separation in seismic rehabilitation At the time of the earthquake, adjacent buildings may also collide with each other due to the displacement created. Therefore, to prevent possible damages, the minimum distance of the building should be determined using the following formula. Appropriate seismic remediation measures should be considered where this is the case [13] (Fig. 2.96). qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi Si . Δ2i1 1 Δ2i2 (2.41)

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Figure 2.95 Failure of parapet wall.

Figure 2.96 Building separation in seismic rehabilitation.

Seismic rehabilitation steps and practical methods in seismic rehabilitation of existing buildings 185

2.3.2.5 Earthquake vertical effects The effect of the vertical component of the earthquake on the response of the building should be considered for: • members and pieces of building; • prestressed members and parts of the building; and • members and parts of the building used under heavy loads of 80% of their nominal capacity.

2.4 Methodology for developing seismic rehabilitation strategies 2.4.1 Philosophy of seismic rehabilitation in compilation of metallurgy Compilation of metallurgy of seismic rehabilitation for existing buildings is to improve stiffness, strength, formability, damping, and decrease hazards of earthquake force. In this regard, the components the cycle below are necessary and must be considered in execution of seismic rehabilitation [7] (Fig. 2.97).

Figure 2.97 Philosophy of seismic rehabilitation in compilation of metallurgy.

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2.4.1.1 A proper look at the damage to choose the type of seismic rehabilitation Seeking out and choosing the optimal seismic rehabilitation solution from a set of possible solutions requires knowledge of decision-making, which seeks to achieve the seismic rehabilitation target while identifying decision variables and limitations. The approach and form of intervention for seismic rehabilitation in existing buildings is aimed at refining and accurately identifying structural and nonstructural damages, it therefore has its own decision variables and constraints. Incomplete understanding of the seismic rehabilitation objective causes confusion in understanding decision variables and constraints. Having a thorough and comprehensive look at the building’s weaknesses and damages is an experiment ament to this claim. Types of rehabilitation patterns include: • prescriptive rehabilitation; • distributed rehabilitation; and • centralized rehabilitation. Each of the seismic rehabilitation patterns is described below. 2.4.1.2 Prescriptive rehabilitation In the seismic rehabilitation of an existing building, with the incorporation of new systems such as base isolation, Dampers, and dampers, the seismic loading is significantly reduced by these new members. In this regard, due to the significant change of applied force to the existing structure, the components with initial strength and stiffness are responsive to earthquake-applied force. This method is costly mainly because it is not concentrated on vulnerable components (Fig. 2.98).

Figure 2.98 Prescriptive rehabilitation method.

Seismic rehabilitation steps and practical methods in seismic rehabilitation of existing buildings 187

Figure 2.99 Centralized rehabilitation method.

2.4.1.3 Centralized rehabilitation Seismic rehabilitation of an existing building with relative strength, but with weak strength, we can increase the stiffness and toughness by improving a limited number of members. For the rest of the members that have not been rehabilitated, they can be controlled as noncore components, regarding the displacements imposed during the earthquake. One of the benefits of this approach is the reduction of the intervention range for improvement. This method is often referred to as repair (Fig. 2.99). For example, the FRP system was used to improve the seismic performance of a concrete beam. In this case, a seismic restoration and rehabilitation with centralized pattern has taken place. 2.4.1.4 Distributed rehabilitation Another way to rehabilitate existing buildings is to use support members and components of distributed in the whole building. This type of improvement, in addition to integrating the entire building properly, will result in a more even distribution of capacity throughout the building and the force applied to the foundation will be greatly reduced. Reinforced structural systems with integrated performance, in addition to being economical, exhibit better strength and performance than the time when two parts of the structure (existing reinforced parts) are separately exposed to earthquake forces (Fig. 2.100).

2.4.2 Evaluating the economic value for seismic rehabilitation for existing buildings One of the important parameters in the process of selecting the methodology of seismic rehabilitation model and estimating the level of

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Figure 2.100 Distributed rehabilitation method.

intervention is the correct estimation of the economic value of the building under study. The following is a model of the value and level of intervention in seismic rehabilitation. A model of the risk level and the seismic recovery process is as follows. Proper usability of technical knowledge and the art of performance are factors that determine the knowledge and technique of restoration and their impact on building performance target must be thoroughly examined. After considering the seismic rehabilitation method suitable for the building concerned, the cost of the project should be taken into account, taking into account the following factors: Xc

KR

EL

AG

Estimated cost of repair

Replacement cost

Estimated life of the building

Age of building

The accepted criteria for nonhistoric buildings do not include the cost of more than 80% of the material residual value of the building. Buildings that are classified within the country’s cultural heritage organization and historical value are exempt from these criteria. The residual value of a building is determined by the replacement cost that decreases with the age of the building relative to the estimated life expectancy, so the relationship between the criteria is expressed as follows: kc # 0:8 3 kR 3

El 2 AG EL

(2.42)

Considering the experience gained in similar projects: The cost of the seismic upgrading of a building should be at maximum 30% of the cost of

Seismic rehabilitation steps and practical methods in seismic rehabilitation of existing buildings 189

Figure 2.101 Evaluating the economic value for seismic rehabilitation for existing building.

Figure 2.102 The construction of the new brace for seismic rehabilitation has eliminated the use of the kitchen entrance.

construction or the economic value of the existing building. Keep in mind, however, that this coefficient is quite an experimental number (Fig. 2.101).

2.4.3 Intervention in architecture Intervention encompasses any activity that disrupts the change in the architectural plan of a building. This change can be seen visually in a variety of hidden and obvious forms (Fig. 2.102). 2.4.3.1 Hidden intervention Creating a seismic improvement plan that is not visually visible in the building’s facades or components. 2.4.3.2 Obvious intervention Creating a seismic improvement plan that incorporates new components into the building architecture plan. These components make changes to

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the building that are visually visible in the building’s facade or components. Below these effects are presented in a diagram to better understand the concepts (Fig. 2.103).

Figure 2.103 Obvious intervention.

Figure 2.104 Performance pattern in seismic rehabilitation targets.

Seismic rehabilitation steps and practical methods in seismic rehabilitation of existing buildings 191

2.4.4 Performance pattern in seismic rehabilitation targets The level of performance, damage, and intervention for each of the seismic rehabilitation targets are presented in Fig. 2.104.

References [1] Iran Road, Housing & Urban Development Research Center (Iranian Standard 2800), Fourth Edition of Building Design Codes Against Earthquake. [2] American Federal Emergency Management Agency (FEMA) (356), Prestandard and Commentary for the Seismic Rehabilitation of Buildings. [3] Islamic Republic Vice Presidency for Strategic Planning and Supervision Office of Deputy for Strategic Supervision, Department of Technical Affairs, Code. No (360), First Revision, Instruction for Seismic Rehabilitation of Existing Buildings. [4] Islamic Republic of Iran Management and Planning Organization, Office of Deputy for Technical Affairs, Technical Criteria Codification & Earthquake Risk, Reduction Affairs BureauCode No. (376), Instruction for Seismic Rehabilitation of Existing Unreinforced Masonry Buildings. [5] Federal Emergency Management Agency (FEMA) (1997), NEHRP Commentary on the Guidelines for the Seismic Rehabilitation of Buildings (FEMA 274), Reston, VA. [6] ASCE (2013), Seismic Rehabilitation of Existing Buildings (ASCE/SEI 41-13), American Society of Civil Engineers, Reston, VA. [7] Federal Emergency Management Agency (FEMA) (2000), Prestandard and Commentary for the Seismic Rehabilitation of Buildings.

Further reading American Concrete Institute (ACI) (318-14), Building Code Requirements for Structural Concrete. American Society of Civil Engineers, ASCE/SEI 710, Minimum Design Loads for Buildings and Other Structures.

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Chapter at the glance

CHAPTER THREE

Types of existing buildings: detailed introduction and seismic rehabilitation Aims By reading this chapter, you are introduced to: • • • •

getting acquainted with all types of masonry existing buildings; learning how to evaluate elements in these buildings; providing seismic recovery practices in these buildings; and providing two fully functional examples to understand the concept of seismic remodeling of building materials.

SUBCHAPTER 3.1

Masonry structure buildings 3.1.1 Introducing types of masonry buildings In civil engineering, the term “masonry structure buildings” generally refers to structures that do not use conventional restrained seismic systems such as moment frames and shear walls. In these buildings, the walls are the main components of the structure. Brick, sand, and cement mortar are used as wall materials. Earthquake load transfer and depreciation are generally carried out by load-bearing walls. The height of masonry buildings is usually less than 10 m up to the foundation level and the number of floors is generally less than 3. The walls in these buildings are divided into two types, that is, structural walls that are designed to restraining earthquake forces, and nonstructural walls that have the same internal partition that are responsible for the separation of interior and architectural

Seismic Rehabilitation Methods for Existing Buildings. DOI: https://doi.org/10.1016/B978-0-12-819959-6.00003-8

© 2020 Elsevier Inc. All rights reserved.

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spaces. Since these structures do not exhibit good resistance to earthquakes, rehabilitation methods that evaluate basic function in short and regular buildings are used to rehabilitate these types of buildings. The main purpose of this function is to maintain the building static and provide safety against earthquake hazard level 1 (BSE-1) as a 475-year return period. Masonry buildings are generally rehabilitated for basic seismic rehabilitation objectives, with some exceptions. In this chapter, the masonry structure building is named as masonry building (Fig. 3.1.1).

3.1.1.1 Scope of implementing the content presented in this section The requirements of this section apply to seismic evaluation and rehabilitation design for traditional masonry buildings and masonry buildings with ties in which all or most of the vertical loads are supported by cement block and brick load-bearing walls [1]. 3.1.1.1.1 Traditional masonry buildings Traditional masonry buildings generally are buildings for which engineering calculations are not performed at the time of construction and execution. The ceiling system used in these buildings usually is wooden, arched brick. The foundations of these types of buildings are generally of traditional foundations, such as stone with sand and brick mortar. Ties have

Figure 3.1.1 Tabriz historical masonry building.

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also been used in traditional buildings in some cases. They are usually made of wood (Fig. 3.1.2). 3.1.1.1.2 Modern masonry buildings Modern masonry buildings refer to buildings in which modern materials are used. In this regard, we can refer to buildings that have ceilings with modern materials such as concrete-block joists, concrete slabs, and walls made of pressed brick, cement blocks, perlite, and so on. The foundations of these types of buildings are generally of concrete or steel material foundations. The two classifications presented for masonry materials mentioned earlier can be divided into two main groups, depending on how the load is distributed among the components according to the type of ceilings, one of the main parameters when assessing vulnerability for seismic rehabilitation. The categorization is as follows: 1. Masonry buildings with rigid diaphragm 2. Masonry buildings with flexible diaphragm In masonry buildings the integrity (coherence) between structural elements such as walls and ceilings is reached through horizontal and vertical ties; these buildings are considered as buildings with ties. Otherwise, the types of buildings in this book are named the traditional masonry buildings (without ties). Generally, material of ties in masonry buildings is steel or reinforced concrete (Figs. 3.1.3
3.1.5). To provide a better insight into the investigation and categorization of elements with respect to the integrity of structure, the masonry buildings separated in the previous section are redivided into two main categories: 1. Masonry buildings with ties 2. Masonry buildings without ties

Figure 3.1.2 Traditional masonry building with stone materials (Shiraz Ghalat Village).

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Figure 3.1.3 Modern masonry buildings with ties.

Figure 3.1.4 Modern masonry buildings without ties.

Figure 3.1.5 Traditional masonry buildings with adobe material.

3.1.2 Understanding potential structural damage It is assumed that you are a civil engineer facing a seismic rehabilitation project for a masonry building. For this purpose, you should have the

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197

ability to identify potential damages that are observable. These damages are divided into five categories in terms of the type of building and the related elements.

3.1.2.1 Damages related to structural walls The first element that catches your attention is the dimension of walls in masonry buildings and their ratios to the materials used in them. Therefore length, height, and thickness of the walls regarding the used materials are observed and evaluated, and qualitative vulnerability is provided. Examples of qualitative and quantitative damages to walls as the most important restrained seismic elements in masonry buildings can include dimensions not compliant with existing building standards. Regardless of the quality and dimensions mentioned at the time of the earthquake, masonry buildings have a general function that is proportional to the total cross-sectional area of the walls in each direction relative to the surface area of that floor. Possible problems in dealing with this parameter are relative wall deficiency in the floors which causes problems such as stiffness, mass incompatibility, and soft story. Also the percentage and dimensions of openings in the walls and their location are very important. For example, the presence of openings next to ties may exacerbate the shearing phenomenon in the ties or the so-called short column. It should be noted that damage to walls, both on and off the plate, must be carefully evaluated (Fig. 3.1.6). The short column phenomenon is more common in the stairwell construction area because in this area the creation of interlayer plates causes asymmetric mass and stiffness deficiencies in the area, and in most cases, the staircase is destroyed during the earthquake and the access to the floors

Figure 3.1.6 Short column phenomenon in vertical concrete ties in masonry buildings.

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is lost. It is recommended that a structural engineer should carefully assess the details of the staircase when entering a building that requires seismic rehabilitation to identify its damage (Fig. 3.1.7). The openings created on the walls are very important in terms of the dimension of the window and the distance from their boundary or vertical ties because the dimension of the openings is very effective in the calculation decisions and ultimately affects capacity evaluation (Figs. 3.1.8 and 3.1.9). Lintel beams in the middle of the wall are used to control on-plane buckling in seismic rehabilitation of the walls (Fig. 3.1.10).

3.1.2.2 Damages related to material quality Weakness in quality of materials and their implementation in the building that can be observed show decrease in strength and stiffness. In addition, weakness in these materials can include the weakness in bound of brickwork, corner, diagonal, horizontal cracks, and so on. Any type of erosion

Figure 3.1.7 Short column phenomenon.

Figure 3.1.8 Opening problem in the wall.

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and corrosion in steel elements, porosity, and other damages mentioned in Chapter 2, Seismic Rehabilitation and Practical Methods in Seismic Rehabilitation of Existing Buildings (Fig. 3.1.11).

Figure 3.1.9 Cracks in a masonry wall.

Figure 3.1.10 Lintel and tie in masonry building.

Figure 3.1.11 Unsuitable quality of materials and their implementation.

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3.1.2.3 Damages related to integrity of components A masonry building consists of walls orthogonal to each other. These walls are connected to each other in traditional methods or modern methods such as vertical and horizontal ties. Lack of ties and lack of walls’ connections lead to damages to integrity in the structure. This damage is directly related to the type of diaphragm system which is explained in the following. Also, the connections and execution of ties must be accurately examined because in most cases, despite the fact that building have horizontal and vertical ties, ties connections are damaged at the time of earthquake and the building is irreparably damaged. Therefore the quality of materials used in ties is of high importance. Fig. 3.1.12 illustrates executing horizontal and vertical ties and their connections to each other to create integrity and finally connection to the roof and foundation.

3.1.2.4 Damages related to roof structures In a masonry building considering the direction floor farming and the stiffness of secondary beams combined with the structural ceiling, the rigidity of the roof is evaluated in terms of earthquake direction and its rigidity is determined. Unusual openings and nonattachment of the components of the roof structure to the structural walls and so on can be considered damage to the roof. Roofing in these buildings is mainly such that the secondary beams are usually placed on the walls. In some cases, the beams are buried at the bottom in a horizontal shaft above the walls. In cases where the beams are positioned directly on the structure walls, the ceiling is vulnerable. This is because the earthquake forces the beams to move excessively and eventually lead to deformations, making the roof have flexible function. Large openings with relatively large dimensions in these types of ceilings indicate its vulnerability. This vulnerability can be

Figure 3.1.12 Lack of wall and facade integrity when building is executed.

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investigated in the presence of staircase floors, building windows, and other openings (Fig. 3.1.13).

3.1.2.5 Weakness in foundation as the common element of structure and soil Inadequate quality of materials, weaknesses in dimensions, inconsistency between interior elements and walls, etc. can be considered as weaknesses in foundations. Soil nonconsolidation or lack of proper system for performing reinforced and unreinforced foundations for building materials can be one of the weaknesses for this part of such buildings. Further, for the purpose of seismic rehabilitation, this part of the building is presented with appropriate methods with numerical calculations. The foundation must also be properly attached to the walls and eventually the structural roof by vertical and horizontal ties so that it can properly transfer the applied load from the earthquake to the soil during an earthquake. For example, in Fig. 3.1.14, the foundation was built on a sloping ground, reinforced with carcasses to correct the soil slope.

Figure 3.1.13 Inappropriate connection of roof to other integrity elements (ties).

Figure 3.1.14 Foundation constructed on high slope.

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In unreinforced foundations, as mentioned in Chapter 1, Understanding the Basic Concepts in Seismic Rehabilitation, dimensions have a significant role to play in determining the capacity. It is recommended to the seismic rehabilitation engineer to determine the type of foundation, reinforced and unreinforced, when categorizing damages of foundation.

3.1.2.6 Weakness in noninstrumental walls and infill (partition) If the infill wall is somehow detached from the frame around it so that it does not deform during lateral displacement of the structure and does not play a role in lateral bearing, it is considered nonstructural. Nonstructural partitions run from the periphery on three sides. However, due to performance problems and weaknesses in wall standing when out-plane loading, separation from the sides is recommended.

3.1.3 Rapid vulnerability assessment As discussed in Chapter 2, Seismic Rehabilitation and Practical Methods in Seismic Rehabilitation of Existing Buildings, some initial quality assessment questions can be used when entering a seismic rehabilitation project during an in-depth visit to the project. According to the explanations given in Chapter 2, Seismic Rehabilitation and Practical Methods in Seismic Rehabilitation of Existing Buildings, an initial qualitative assessment of the vulnerability is possible using a set of questions. Rapid vulnerability assessment in masonry buildings can be carried out according to Iranian seismic rehabilitation codec 360 and Iranian masonry seismic rehabilitation codec 376, presented for the evaluation of existing masonry buildings. In this regard, as mentioned in Chapter 2, Seismic Rehabilitation and Practical Methods in Seismic Rehabilitation of Existing Buildings, we can reach a quantitative number based on the qualitative evaluation by using some tables. This number, in its own range, can estimate the building vulnerability. In the presented model, the author has tried to categorize these tables in different geographies so that if the details are increased, the reader can reach the most precise qualitative number by generalizing the parameters. Rapid vulnerability assessment [1]: • Using the checklist provided in Chapter 2: Seismic Rehabilitation and Practical Methods in Seismic Rehabilitation of Existing Buildings.

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•

Providing rapid vulnerability assessment for masonry buildings. As discussed in Chapter 2, Seismic Rehabilitation and Practical Methods in Seismic Rehabilitation of Existing Buildings, the evaluation of existing buildings has a highly important section, qualitative vulnerability evaluation. This falls into five main parts each of which determines the accuracy of calculations and operations. Quality of the materials used in masonry buildings: 1. Percentage of the relative wall as the most effective element in masonry buildings. 2. Integrity systems between lateral restrained seismic elements. 3. The type of diaphragm as a determiner element for lateral loadabsorbing system. 4. Weakness in foundation as the common element between the structure and soil.

3.1.4 Comprehensive assessment of vulnerabilities in masonry buildings for reporting This section is the most important part in seismic rehabilitation studies which falls into four main subsections: 1. Preparing as-build plans 2. Examining structural components 2.1 Examining and analyzing test results 2.2 Calculating loads applied to the building 2.3 Assessing and analyzing quantitative vulnerability of structural components 3. Examining nonstructural components 3.1. Examining and analyzing quantitative vulnerabilities of the nonstructural components 4. Conclusion

3.1.4.1 Preparing as-built plans As-built plans for masonry buildings are plans that are prepared due to the absence of main plans of the building or that are plans drawn based on inspections and digging and used in vulnerability reports. Names of the drawn plans are: • foundation plan;

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• • • • • • • •

floors plan; detail plans for structural walls; detail plans for nonstructural walls; floor farming plan; plan for load-bearing and nonload-bearing walls situation; ties situation plan; connections plan; and plan for explaining current status. It must be noted that at the end report, the plan for separating loadbearing walls are attached to the plans above for analysis.

3.1.4.2 Evaluation of structural components—analyzing test results As mentioned in the preceding section, the structural component review consists of two main parts, the first part of which is to examine and analyze the results of the tests, in the beginning of the report a checklist containing the specifications of the test or digging, together with images provided in tables. This section provides an example of a checklist of tests. The sample in Table 3.1.1 (Fig. 3.1.15) [1,2]. 3.1.4.2.1 Material strength tests In this part of the report, based on the results of the tests, the highest strength and expected strength of the building materials should be extracted and used in the report. In the following are some examples of test results: • mortar shear capacity; • coring concrete; • Schmidt Hammer test; • tensile capacity of rebar’s in ties and foundation; and • steel profile tensile capacity in roof and stairway components. 3.1.4.2.2 Geotechnical tests The results of these tests are mainly used in the evaluation part of the foundation alignment. All the geotechnical tests mentioned in tests and digging section in thorough vulnerability analysis and the evaluation of masonry buildings, regarding the lateral seismic system, mainly load-bearing walls, we can determine shear strength of masonry materials Vme which is the most important factor in the analysis. In the next step, it is also important to

Table 3.1.1 Checklist for examining and collecting foundation information. Position of digging Project name and code . . .. . .. . .. . .. . .. . .. . . Digging code Date Digging objective Digging result

Digging specifications

Flooring specifications

Additional specifications Scanning

Height of foundation Height of lean concrete Flooring height Foundation type Width in direction X Width in direction Y Framing type The appearance of foundation concrete The φ8@30 cm appearance of lean concrete Description of the flooring layers

Wall material on foundation Wall thickness on foundation Mortar specification on wall Scanning location status Scanning location Number of rebar’s in direction X

Date of digging

H-14

Plans

Final results

Cm50 Cm5 Cm110 Strip Northern-southern Along eastern-western Brick Fairly good











Cm50 Cm5 Cm110 Strip North to south East to West Brick Fairly good

Mosaic 3 cm Cement sand mortar cm8 Hand soil cm110 Compressed brick 40 cm Sand cement









Mosaic cm3 Cement sand mortar cm8 Hand soil cm110 Compressed brick 40 cm Sand cement

6φ14




6φ14 (Continued)

Table 3.1.1 (Continued) Position of digging

Concrete coring

Sampling from the reinforcement

Vertical ties

Project name and code Digging code Digging objective

. . .. . .. . .. . .. . .. . .. . . Date Digging result

Date of digging

H-14

Plans

Final results

Number of reinforcement in direction Y Concrete cover thickness Diameter of the core Height of the core Reinforcement in the core Number of rebar’s in the core Appearance of the core Sampling situation Concrete cover Number of the reinforcement Length of the reinforcement Erosion status of the reinforcement Ties dimension Number of ties reinforcement Specifications of stirrup Erosion of reinforcement

6φ14 Stirrup φ8@30 cm 5 cm 913 218








6φ14 Stirrup φ8@30 cm Cm5 913 218

40 cm in 40 cm 4φ14




40 cm in 40 cm 4φ14 φ8@30 cm

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Figure 3.1.15 Concrete coring from roof.

determine compressive strength of masonry materials Fme , elastic module of masonry materials Eme , and shear module of masonry materials Gme to determine element capacity. Regarding the importance of this section in preparing thorough report on vulnerability, after recording each in quantitative vulnerability report, results must be analyzed quantitatively, and finally the obtained results are used in the other parts of the report.

3.1.4.3 Quantitative vulnerability evaluation and analysis of structural components 3.1.4.3.1 Part 1: Calculating loads on the building In quantitative evaluation to calculate and estimate indices such as compressive stress, average gravity stress, overturning moment, resistance moment, and calculating base shear, we need to calculate gravitational loads of structure which is effective in calculating the abovementioned factors. Therefore in calculating gravitational items, mainly four important items, namely ceilings, lateral load-bearing walls, shelter, and mechanical facilities on roof if any are considered. Live loads of building and loads from earthquake shake and snow are separately calculated and recorded in the tables. Calculation of all load indices of gravitational loads as loads implemented on the building and calculations related to earthquake load are performed according to the regulation of designing buildings against earthquake. Tables for gravitational loads on masonry buildings are: • structural load-bearing walls; • ceilings of floors; • stairways; • shelter; and • other unpredicted items.

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In addition, tables for loading live loads QL must be provided in the report. 3.1.4.3.2 Part 2: Numerical vulnerability analysis The second part of quantitative vulnerability analysis is related to numerical vulnerability analysis of structural components. In masonry buildings, considering that load-bearing walls are the most important decaying agent for earthquake force, they must be examined first, and other elements such as ceilings and ties must be taken into consideration in other steps. 3.1.4.3.2.1 Modeling structural load-bearing walls

The first step in modeling load-bearing walls is to determine the type of masonry building. • structural load-bearing brick walls with vertical and horizontal ties • structural load-bearing brick walls without ties After identifying the type of structural system based on the digging and plans prepared, we begin to model, since structural modeling is mainly done manually using database generating software. Modeling tips for load-bearing walls in types of masonry buildings with ties: • Masonry buildings with ties • Determining complete position of ties on plans. • Completely determining the height of floors. • Accurately determining foundation alignment. • Separating load-bearing walls in main directions between vertical and horizontal ties with thickness more than 20 cm. • Determining the type ceilings diaphragm. Modeling in traditional masonry buildings is similar to that of a masonry building with ties. Except that the load-bearing walls are separated in the main directions between the back supports. The next step is to determine seismicity of each wall regarding the numbering and separation. In this step, each of the load-bearing walls is taken into consideration based on the type of diaphragm and the amount of earthquake force it absorbs, therefore, at first, the type of diaphragm including rigid and flexible must be studied. In masonry buildings, whether traditional or with ties, if the diaphragm of the structure is rigid, each of the components absorbs earthquake force in objective direction with ratio of component stiffness to story stiffness. Also in buildings with flexible diaphragms, each

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of the components contributes to earthquake force absorption based on mass ratio (Figs. 3.1.16 and 3.1.17) [2,3]. In preparing complete vulnerability report, the type of diaphragm is not the only criterion for diaphragm performance. This performance must be quantitatively evaluated and analyzed for each diaphragm. Also, in case the ceilings are rigid, the effect of torsion must be fully provided in the analysis. After modeling, results must be evaluated and defects in the building must be identified. Defects and the related evaluation are as follows. 3.1.4.3.3 Part 3: Identification and analysis of defects in a building Assessing the masonry buildings complete vulnerability assessment and providing seismic rehabilitation design as mentioned in first part, the first

Figure 3.1.16 The difference between rigid and flexible diaphragms in masonry building.

Figure 3.1.17 Break walls in flexible diaphragm buildings.

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step is to study and prepare seismic rehabilitation notebooks to identify the type of building according to the materials presented in the masonry building type section. After identifying and objectively examining the materials, the defects of the studied building will be investigated and identified. According to the criteria of the type of masonry building’s system structure, defects will be evaluated according to criteria stated in the journal as explained in the following. 3.1.4.3.3.1 Evaluation and identification of the defects in traditional masonry buildings

In traditional masonry buildings, the most commonly used materials include structural materials, the structural system in the building, the main and secondary load-bearing walls, the diaphragm (rigid or flexible), and the structural and nonstructural joints. 3.1.4.3.3.1.1 Defects of materials used in the building In examining the materials used in the construction of traditional masonry buildings, major defects in materials include poor quality and load capacity of masonry units used, whether brick or cement block. It should be noted that in such buildings, the low strength and adhesion strength of the mortar cannot provide the required mortar shear strength. 3.1.4.3.3.1.2 Defects of structural system of the building Common structural defects in traditional masonry buildings can be due to incomplete load paths and insufficient shear strength of buildings, inability of the building to maintain vibration integrity, lack of secondary auxiliary systems such as collapses, irregularities in plan, irregularities in height, the lack of appropriate foundations, and the lack of sufficient distance from the adjacent building. In the appraisal section of the masonry structures, the applied case series is thoroughly discussed. 3.1.4.3.3.1.3 Defects in load-bearing walls Major deficiencies of conventional load-bearing walls in traditional building materials can be incorrect implementation of building units layout, empty seams between mortar joint, height-to-thickness ratio of wall, unbraced wall length, so high wall, low wall density due to large openings, proximity of openings to the walls boundary, toothing in executing walls, placing the beams directly on the wall, improperly restraining the floor arch against the thrust force, and passing the pipe and the chimney through the wall (Fig. 3.1.18).

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Figure 3.1.18 Toothing in brick wall.

3.1.4.3.3.1.4 Diaphragm of ceiling (rigid or flexible) The most common uses of ceilings in traditional building materials can be high roof weights, incoherence and irregularity of ceilings, insufficient length of ceilings beams, lack of openings in the roof, and high span to ceiling width ratio. 3.1.4.3.3.1.5 Connection of structural components The major disadvantages of common structural member connections in traditional masonry buildings can be inadequate connection between load-bearing walls, inadequate connection between load-bearing walls and ceilings, and inadequate connection between blades and load-bearing walls or onstructure wall and ceilings. 3.1.4.3.3.1.6 Nonstructural elements of masonry materials Defects of connections in nonstructural component in traditional masonry buildings can be the high weight and low strength of nonstructural walls, improper connection between the facade and the wall, unstable parapet (curb-wall), and chimneys. 3.1.4.3.3.2 Evaluation and identification of the defects in masonry buildings with ties

Common defects of masonry buildings with ties are all the defects in traditional masonry buildings except for the cases where beams are placed directly on the wall, cases with inability of the building in maintaining integrity at the time of vibration, cases without a secondary system such as ties. It must be noted that less defects are observed in ties control section. These defects include not using connection for vertical and horizontal ties in foundation level, inadequacy of number and distance of ties, dimensions of bars and using them, weakness in concrete ties materials, have no

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connection in ties bars and inadequacy of their overlaps in connections, separation in ties due to implementing high openings or existence of halffloor, separation in ties due to existence of pipes and chimney, and inappropriate connection between walls and ties. 3.1.4.3.4 Quality control of masonry materials units 3.1.4.3.4.1 Traditional masonry buildings

In traditional masonry buildings, quality control of masonry units is done by visiting the units. There must be no breaks or cracks in appearance of masonry units. 3.1.4.3.4.2 Masonry buildings with ties

Quality control of masonry units in masonry buildings with ties is performed as in traditional masonry buildings. 3.1.4.3.5 Quality control of mortar 3.1.4.3.5.1 Masonry buildings

Quality control of mortar in traditional masonry buildings is one of the important factors in determining shear capacity of load-bearing structural walls. For this purpose, according to the following criteria, for the abovementioned walls, the number of mortar shear capacity tests should be carried out according to the proper number in suitable height, which will lead to Vme tests results. For masonry buildings with ties, the quality control of mortar used in masonry building with ties is similar to traditional masonry buildings. 3.1.4.3.6 Control of load path In masonry buildings, both traditional and with ties, structural walls are considered as the main resistant system against lateral force of earthquake. Designing this type of system should be such that it is able to transfer earthquake force from the floors to the foundation of the structure. In addition, the load path has to be complete. Materials in this system should have the necessary and adequate strength to tolerate the applied loads. In case the load transfer path is interrupted, the building is vulnerable in terms of load path and requires seismic rehabilitation. 3.1.4.3.7 Integrity of masonry building In masonry buildings, the integrity between all structural elements including foundation, roof, and load-bearing walls must be provided

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appropriately with horizontal and vertical ties according to criteria presented in the first section “masonry buildings with ties.” Buildings without ties or buildings with ties that do not follow the mentioned criteria are considered vulnerable in terms of integrity and need seismic rehabilitation according to the methods in the following. 3.1.4.3.8 Irregularity in plan This subject is common between traditional masonry buildings and buildings with ties. If any of the following criteria is not followed and implemented in seismic evaluation of masonry buildings, the building is considered vulnerable. • The distance between the center of stiffness and the center of mass of each floor in each of the two major axes shall not exceed 20% of the dimensions of the building on that axis. • Building plan is symmetrical relative to main axis. • Protruding dimensions in building plan. • The length of the building must not exceed three times its width. • There must be symmetry relative to two main axes. • Protrusion and concavity dimensions must be suitable. 3.1.4.3.9 Irregularity in height Irregularities in height are common to traditional masonry buildings and masonry buildings with ties. These criteria include examining weak floor, irregularity in geometry, mass, and vertical inconsistency. In seismic evaluation of masonry buildings, in case any of the criteria mentioned in the following are not considered and met, the building will be considered seismically vulnerable. 3.1.4.3.10 Soft or weak story If the story shear strength of a building is less than 80% of its upper story shear strength, the building will be evaluated for poorly vulnerable stories and needs to be provided with shear strength in that story. 3.1.4.3.11 Irregularities in geometry An irregular building in geometry is called a building that, in one of the horizontal dimension’s x and y, is 30% larger than the horizontal dimension of its upper or lower floors.

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3.1.4.3.12 Irregularities in mass A building irregularities in mass is a building in which the effective mass of a story is 50% greater than the effective mass of adjacent stories, both upper and lower. 3.1.4.3.13 Inconsistency in vertical direction A building is considered irregular in vertical direction when load-bearing structural walls in it are not expanded to foundation level, and there are interrupted in upper-floor levels. In this situation, load transfer path is not also complete, and the building is seismically vulnerable.

3.1.4.4 Foundation Foundations evaluation criteria are common to masonry buildings and buildings with ties. It should be noted that the foundation of masonry buildings is generally used to withstand the load received from the loadbearing walls. If the foundation of the load-bearing walls is made of materials such as nonreinforced concrete or foundation paste and boulder, the depth and width of the foundation must be at least twice the thickness of the wall. In cases where the foundation is used for reinforced concrete materials, the criteria set out in the foundation evaluation Section (3.2.4.4.3) should be used. The foundation should be implemented as an integrity of homogeneous materials under the load-bearing structural walls.

3.1.4.5 Adjacent buildings This subject is the same for masonry buildings and buildings with ties, and it is about the criteria related to the height of adjacent buildings and their distance from each other. Adjacent buildings are the buildings with distance less than 1/100 from each other relative to the height of shorter buildings. Criteria for nonvulnerability are as follows: • The ratio of the adjacent building height to the studied building must not be more than 50%. • The ratio of floor levels in adjacent buildings to the studied building must not be more that 50%.

3.1.4.6 Quantitative numerical vulnerability evaluation of load-bearing structural walls Qualitative evaluation of load-bearing structural walls is done through the following steps:

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Modeling and figuring the masonry building in directions X and Y depending on the type of structure including with or without ties • Determining materials specifications. • Complete loading on the structure and determining gravitational loads. • Calculating and determining the structure weight, W. • Determining basic shear force. • Determining shear force for each floor. • Sorting and preparing tables for structural walls for each floor based on diaphragm rigidity. • Determining structural walls strength and preparing force-to-capacity ratio. • Determining vulnerability of walls qualitatively. To evaluate vulnerability of structural components qualitatively in masonry buildings, the first step is to determining the total weight of structure, W, regarding the gravitational loads and percentage of live load weight percentage. Weight 5 QD 1 QL 1 QS

(3.1.1)

Regarding that one the main steps in determining lateral earthquake force is in floor level. Therefore the weight of floors must be calculated separately. 3.1.4.6.1 Calculating basic shear force on building Base shear force is determined using the topics presented in Section 2.3.2.2.1.1.5. In fact, we can use the following simplified formula to calculate the basic shear force for masonry building: V 5 Sa 3 W

(3.1.2)

3.1.4.6.2 Geotechnical test results to determine the type of soil To determine the soil type of the site, the shear-wave velocity and the type of soil layers obtained from the boring should be extracted and used. Shear-wave velocity is determined in 30 m distance from the ground regarding the thickness of different layers. This speed can be calculated through the following equation (Table 3.1.2) [4]: P di  Vs5 P (3.1.3) di =Vsi 3.1.4.6.3 Evaluating shear capacity This section of analysis includes: • evaluating shear capacity of walls; and • evaluating shear capacity of story.

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Table 3.1.2 Soil type example. Types Materials

VS (m/s)

One

.750

Porphyry (with gross texture and grains), sediment hard stones with high strength, and gneiss (condensed soil and sand) with thickness less than 30 m on stone bed Two Loose porphyry (e.g., Tuff), laminated sedimentary loose gneiss stones, and all the stones that has become loose due to being exposed to weather Three 1. Crushed stones due to being exposed to weather 2. Soil with average density, floors of soil and sand with average bonds between grains and clay with average stiffness Four 1. Soft deposes with high humidity due to abundance in underground water 2. Any type of soil profile which includes 6 m clay with plastic appendix more than 20 and humidity higher than 40%

375 # V s # 750 175 # V s # 375

,175

Source: From Iranian earthquake codec 2800.

3.1.4.6.3.1 Evaluating shear capacity of walls

In masonry buildings, evaluating shear capacity of walls is the most important part of sections in preparing report on vulnerability of the building. In this section, shear capacity of each wall is determined and compared with contribution of shear force applied to them, and finally vulnerability of components is determined. The procedure to calculate and prepare tables of specifications is explained in the following. 3.1.4.6.3.1.1 Specifying the type of diaphragm rigidity Since the type of earthquake lateral force distribution among the members depends on the type of diaphragm rigidity, the diaphragm rigidity is the most important part of initiating quantitative vulnerability assessment of masonry building as described in previous chapters. Specifying the distribution of lateral earthquake force between components: • Rigid diaphragm In this type of diaphragm, the distribution of earthquake lateral force among the members is relatively difficult. To prepare the lateral force distribution tables between the walls of the building we need to calculate the stiffness of each member. • Flexible diaphragm In a flexible diaphragm, the distribution of earthquake lateral force is distributed among the seismic members in terms of the effective mass ratio.

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3.1.4.6.3.1.2 Evaluating contribution of shear force cause from earthquake 3.1.4.6.3.1.2.1 Walls with rigid diaphragm In this diaphragms, earthquake shear force is distributed based on effective stiffness of each wall. • Determining lateral stiffness of walls Stiffness of walls with masonry materials that are effected by inplate force is determined in two ways based on the location and performance or based on considering flexural and shear shapes. It must be noted that the mentioned analysis in here is linear. • Nonreinforced masonry material walls Lateral in-plate stiffness of wall is calculated with the following equation [1
3]:   3  heff heff (3.1.4) 1 K 5 1= 3Em Ig Av Gm •

Wall between openings Accordingly, lateral in-plate stiffness of walls between openings that cannot rotation in-plateand and the stiffness of the walls between openings that are closed from top to bottom against rotation is evaluated based on the following equation:   3  heff heff K 5 1= 1 (3.1.5) 12Em Ig Av Gm

•

After determining the in-plate lateral stiffness of wall, the ratio of the wall stiffness to the total stiffness of the story should be calculated. Using this ratio, we can calculate the percentage of wall shear contribution from whole floor shear. 3.1.4.6.3.1.2.2 Evaluation of shear capacity of walls with flexible diaphragm In buildings with flexible diaphragm, after determining the effective mass of the wall, its ratio to the whole walls of story in the desired direction is calculated and finally the contribution of the wall from the whole floor shear force is calculated according to this ratio.

3.1.4.6.3.1.3 Steps in calculating shear capacity of walls • Calculating average gravitational stress for each wall. • Extracting shear capacity of mortar from tests. • Calculating permitted shear stress of each wall. • Calculating section area. • Shear strength of walls.

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3.1.4.6.3.1.3.1 Calculating section area (area of net mortared/grouted section of a wall or pier) As can be seen in Fig. 3.1.19, the shear net section of the

mortar for the walls in nonreinforcement masonry buildings is equal to the surface area of the wall, except the finishing material on surface and facade. 3.1.4.6.3.1.3.2 Evaluating vulnerability of shear capacity of a floor (story) The vulnerability assessment is done according to the total cross-sectional area of the structural walls. In examining the set of walls, the following two items are required (Table 3.1.3): • In this type of evaluation, the total cross-sectional area of all walls should be at least 75% of the table presented. • The total cross-sectional area of the walls shall not be less than Ai resulting from the relation: Ai 5

Vl Va

(3.1.6)

3.1.4.6.3.1.3.3 Investigation of in-plate behavior of walls and bases of masonry materials The most important parameter in this section is the determina-

tion of stiffness, strength, and acceptance criteria of nonreinforcement masonry walls within their plate. This applies to walls that are fixed against a rotation and the bases between doors and windows that are fixed against a rotation (Fig. 3.1.20).

Figure 3.1.19 Net section area of wall. Table 3.1.3 The relative minimum wall along floors. Type and number of floors Basement (%) First floor (%)

Brick buildings Buildings with concrete block Stone buildings

One-story Two-story One-story Two-story One-story Two-story

6 8 10 12 8 10

4 6 6 10 5 8

Ground floor (%)


4
6
5

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Expected masonry shear strength capacity (Vme) Expected masonry shear strength capacity for each wall is calculated through the following equation (Table 3.1.4). For walls with one layer of brickwork:   PCE Vme 5 0:5Vto 1 0:75 (3.1.7) An For walls with more than one layer of brickwork:   PCE Vme 5 0:375Vto 1 0:75 An

(3.1.8)

Evaluating wall strength in linear method As mentioned in Chapter 2, Seismic Rehabilitation and Practical Methods in Seismic Rehabilitation of Existing Buildings, behavior of building elements is divided into two categories, namely, force controlled and deformation controlled [1
3]. • In masonry buildings, the strength for deformation-controlled efforts is the expected strength QCE which includes sliding shear distribution modulus and barrel shear distribution modulus. • In masonry buildings, the strength for force-controlled efforts is the minimum strength QCL which includes diagonal tension stress and wall’s hell compression tension.

Figure 3.1.20 Illustration of effective height and displacement for walls and bases. Table 3.1.4 Description the parameters use for calculating Vme . Row Parameters Description

1

PCE

2

An

Expected gravity compressive force applied to a wall or pier component considering load combinations—Eqs. (2.11) and (2.12) Area of net mortared/grouted section of a wall or pier

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Expected lateral strength, QCE The expected lateral strength for masonry walls, including reinforced and nonreinforced, is equal to the least extracted strength obtained from two destruction modulus, expected shear strength of shear crash modulus and barrel moving modulus. Calculation of these strength modes is further explained in the following: 1. Excepted shear strength of mortar for sliding failure mode Vbjs The sliding shear failure modulus causes slight corrosion in the walls and materials and does not limit its displacement capacity. This failure mode is of formable failure modes. The value of this mode for each wall is calculated using the following equation (Fig. 3.1.21): Qce 5 Vbjs

Vbjs 5 Vme An

(3.1.9)

2. Expected barrel movement strength for rocking failure mode Vr During the earthquake and its reciprocating loads, the wall alternately bends over its toes and heels and begins to overturn. However, since the force of the earthquake is instantaneous, this reversal does not last for a few moments and soon shifts the forces’ direction and moves in the opposite direction. These bending movements are called rocking; it is like cradle movements. This failure mode is also a relatively formidable failure. Its value is calculated from the following equation. α equal to 0.5 for fixed-free cantilever wall or equal to 1.0 for fixedfixed pier (Fig. 3.1.22).   L Qce 5 Vr 5 0:9αPE (3.1.10) heff Lower-bounded lateral strength QCL For masonry buildings, QCL , is the least extracted strength obtained from two stresses, diagonal tension stress and comparison pressure of hells of wall, which is calculated as in the following: 1. Lower-bounded lateral strength based on diametric failure Vdt

Figure 3.1.21 Sliding shear failure modulus.

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221

Lateral force in wall plate creates a high compressive stress along the diameter. Perpendicular to compressive stress, there is tensile strain. When a tensile strain is higher than strain of cracked wall materials, diametric crack occurs. This type of failure is common in the center of wall, and continues along the compressive diagonal until it reaches the corners of the wall. The value of tensile strain is calculated through the following formula (Fig. 3.1.23): 1:1ðQD 1 QL ÞUðloadarea Þ 45 L  sffiffiffiffiffiffiffiffiffiffiffiffiffiffi L fa 0 Qcl 5 Vdt -Vdt 5 f dt An 11 0 heff f dt fa 5

(3.1.11) (3.1.12)

2. Lower-bounded shear strength based on compression stress of heel of wall Vtc This type of failure occurs due to high compressive stress in compressive corners (heel) of a wall as a result of reciprocal movement of the wall at the time of earthquake. Hits from this movement crushes hell of wall and reduces the effective length of the wall, thus making the wall weaker against further hits. When displacement inside a floor

Figure 3.1.22 Wall rocking modulus.

Figure 3.1.23 Diametric failure.

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increases, corner crush continues until wall material (masonry buildings) in wall corners are thrown out of the wall (Table 3.1.5; Fig. 3.1.24).    L fα QCL 5 Vtc -Vtc 5 αPL 12 (3.1.13) heff 0:7f 0m Lower-bounded compression strength PCL QCL 5 PCL -PCL 5 0:80ð0:85f 0m An Þ Evaluation of wall strength in nonlinear method In-plane lateral strength of walls and bases is deformation controlled if their expected strength is lower than their minimum strength. Otherwise, it is force controlled. Axial pressure in walls and bases is considered force controlled. Acceptance criteria 1. Acceptance criteria for linear method

Table 3.1.5 The parameters needed to calculate the capacity. Row Parameters Description

1

fa

2

f 0dt

3 4 5 7 8

An heff L f 0m

9

PE PL

Compression stress from gravitational loads according to load composition minimum diagonal tensile strain of masonry buildings equal to Vme Area of net mortared/grouted section of a wall or pier Height to resultant of lateral force Length of wall or pier Lower-bound masonry compressive strength Expected axial compressive force due to gravity loads specified—Eq. (2.9) Lower-bound axial compressive force due to gravity loads specified—Eq. (2.10)

Figure 3.1.24 Stress at the heel of the wall.

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Attempts at main and noncore members that are deformation controlled should satisfy the following equation. m K QCE $ QUD

(3.1.14)

m is the correction factor based on the nonlinear behavior of the member, which is determined based on the different levels of structural performance as shown in Table 3.1.6. 2. Efforts in main members and nonmembers that are force controlled should satisfy the following relationship: KQCL $ QUF

(3.1.15)

where QCL is the minimum strength of a member considering all the efforts that are made to each member at the same time. If nonlinear analysis method is used for the evaluation of masonry structures, it is recommended to consider the following criteria: 1. The stiffness of the components should be considered as linear relationships. 2. Nonlinear force and deformation relationships must be determined as follows for the walls. The general curve of the deformation force can be used in accordance with Fig. 3.1.25 with the parameters percent C, d, e defined for the walls (Table 3.1.7). The relative displacement of the wall or base is equal to the ratio of the effective lateral changes between two ends to its effective height.

3.1.4.7 Analysis of foundations and existing retain wall Masonry retain walls should be evaluated against the effects of seismic and static pressures caused by the soil in accordance with the following criteria (Fig. 3.1.26). Table 3.1.6 Define m factor. Imitating Immediate behavioral mode occupancy

Primary Life safety

Collapse Life prevention safety

Collapse prevention

Sliding shear

1.0 1.0

3.0 2.0

4.0 3.0

8.0 6.0

1:5 heff =L 1:5 heff =L

3:0 heff =L 4:0 heff =L 2:0 heff =L 3:0 heff =L

With ties Without ties Rocking With ties Without ties

Secondary

6.0 4.0

6:0 heff =L 8:0 heff =L 4:0 heff =L 6:0 heff =L

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Figure 3.1.25 Wall deformation diagram.

These elements as soil preservatives should be evaluated against the effects of seismic pressures. In the absence of project-specific geotechnical studies, soil overpressure during an earthquake on a building wall that maintains an unsaturated soil mass with a horizontal level above the groundwater level can be calculated from (Table 3.1.8): ΔP 5 0:4 Kh UγUH

(3.1.16)

3.1.4.8 Evaluation of other load-bearing walls specifications As mentioned earlier, in masonry building materials the process of quantitative evaluation of structural walls in the form of rigid and flexible diaphragms is the same at all stages. The only difference is in the segregation of earthquake forces among the members, which is in the rigid diaphragm in stiffness and in the flexible type in terms of mass. Finally, to detect the vulnerability of the walls if the shear strength of the earthquake is less than or below the expected shear strength of 1 or more, the vulnerable wall is otherwise vulnerable to earthquake forces and does not require seismic rehabilitation. In assessing the vulnerability of load-bearing walls, it is necessary to control the following (Fig. 3.1.27): • execution control of masonry units; • Control ratio of height to wall thickness; • wall height control; • free wall length control; • wall density control; • control the distance of the openings from the bottom of the wall; • controlling the toothing of wall; • control of load-bearing beams on the wall; • thrust force control on floor arch ceiling; and • pipe and chimney inside load-bearing walls.

Table 3.1.7 Nonlinear parameters value and limitation. Modeling parameters Imitating behavioral mode

Sliding shear Rocking

With Ties Without Ties With Ties Without Ties

Deformation

Performance level Residual stress ratio

e%

d%

C%

0.8

0.4

0.6

0:8 heff =L

0:4 heff =L

0.6

IO%

0.1 0.1 0.1 0.1

Primary components

Secondary components

LS%

CP%

LS%

CP%

0.3 0.2 0:3 heff =L 0:2 heff =L

0.4 0.3 0:4 heff =L 0:3 heff =L

0.6 0.4 0:6 heff =L 0:4 heff =L

0.8 0.6 0:8 heff =L 0:6 heff =L

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Figure 3.1.26 Retain wall. Table 3.1.8 The parameters needed to calculate the ΔP. Row Parameters Description

1 2 3

H γ K

Wall height Weight of soil volume unit behind wall Earthquake horizontal acceleration factor at ground level relative to gravity acceleration

Figure 3.1.27 Control ratio of height to wall thickness.

3.1.4.8.1 Execution control of masonry units In traditional masonry buildings and buildings with bricks or blocks, applying masonry walls should be as follows: • Bricks or cement blocks should be arranged so that the required horizontal overlap between masonry units occurs and vertical seams do not overlap. • At least 10% of the wall surface should be included to connect the inner bound of brickwork to the outer. • Width of possible diagonal cracks due to heterogeneous wall ridge should not exceed 3 mm.

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•

The masonry units on the wall should have a smooth, continuous surface and the wall should not be protruded or tilted.

3.1.4.8.1.1 Control of vertical bound of brickwork

In traditional masonry buildings and buildings with ties, it should be completely filled with appropriate mortar. 3.1.4.8.1.2 Control of height to wall thickness ratio

In traditional masonry buildings and buildings with ties to evaluate the stability and control of strength outside the wall plate, the following needs to be quantitatively controlled. The ratio of height to wall thickness (h/t) should be within Table 3.1.9 [3]. 3.1.4.8.1.3 Wall height control

In traditional masonry buildings and buildings with ties, the free height of the masonry materials wall must not exceed 4 m. 3.1.4.8.1.4 Free wall length control

In traditional masonry buildings and buildings with ties, the free wall length shall not exceed 5 m. 3.1.4.8.1.5 Wall density control

In traditional masonry buildings and buildings with ties, the size and position of openings in the wall shall be as follows: • The total area of openings in each load-bearing wall shall be less than one-third of that wall area. Table 3.1.9 Define h/t ratio [3]. Wall types Low relative risk High relative risk SX1 # 0:24 g 0:24 g # SX1 # 0:37 g

Walls in one-story buildings First floor walls in multistory buildings Top floor walls in multistory buildings All other walls

Very high relative risk SX1 $ 0:37 g

20

16

13

20

18

15

14

14

9

20

16

13

228

• •

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The total length of openings in each load-bearing wall must be less than half of the wall length. The horizontal distance of the two openings shall not be less than two-thirds of the height of their smallest opening and not more than one-sixth of their total length. Otherwise, the wall between the two openings is considered a part of the opening and should not be considered as a load-bearing wall. Therefore the lintel beam on the openings must also be integrated with the span having the same length as the openings plus the wall between them. The opening dimensions shall be less than 2.5 m in height and length. Otherwise, the vertical ties shall be fitted on the sides of that are attached to the upper and lower horizontal ties of the floor. The opening lintel beam should also be restrained in vertical ties.

3.1.4.8.1.6 Controlling the openings distance from the bottom of the wall

In traditional masonry buildings and buildings with ties, the distance of the first opening in the wall from the outside of the building shall not be less than two-thirds the height of the opening unless it is situated on either side of the opening unless there are vertical ties on sides of the opening. 3.1.4.8.1.7 Control of the toothing

In traditional masonry buildings, the toothing is regarded as a break point in the wall. 3.1.4.8.1.8 Controlling load-bearing beams of the ceiling mounted on the wall

In traditional masonry buildings, if the ceiling load-bearing beams are located directly above the wall of the masonry materials, a suitable wooden, steel, concrete, or support under the beams should be used. Otherwise, in the common section of wall and ceiling the wall is considered a seismically vulnerable. 3.1.4.8.1.9 Pipes and chimneys inside the load-bearing wall

In traditional masonry buildings and buildings with ties, the following conditions must be observed for pipe and chimney control within loadbearing walls. • The diameter of the pipe or chimney passing through the wall should not be more than one-sixth the thickness of the wall.

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3.1.4.8.2 Evaluation of ceilings in masonry building In assessing the vulnerability of ceilings, it is necessary to control the following: • Ceiling weight. • Ceiling uniformity and consistency. • Base length of ceiling beams. • Opening in the ceiling. • The ratio of the length of the opening to the ceiling width. • The examination of the uniformity and consistency of the ceiling depends on limitation. 3.1.4.8.2.1 Support of length of ceiling beams

The following conditions must be observed to control the support length of the joist. Support length of joist shall not be less than 20 cm or more than 20 cm. 3.1.4.8.2.2 Openings in the ceiling

The following conditions must be observed to control openings in the ceiling. • The total opening area in the diaphragm should be less than 50% of the total diaphragm area. • The opening length adjacent to the wall must be less than one-fourth the length of the wall. • Maximum length of openings adjacent to the load-bearing walls is 2 m. 3.1.4.8.2.3 Ratio of ceiling for span to width

The following conditions must be observed to control the ratio of the span length to the ceiling width. • The diaphragm width to span ratio in flexible ceilings is greater than 3. 3.1.4.8.2.4 Thrust force control on floor arch

In traditional masonry buildings, if the following conditions are seen in diggings, the building is seismically vulnerable in terms of the floor arch. • In the outer-span of the building, if the ratio of the height of the floor arch is more than half of regular diameter. • If the ratio of first-bounded is less than 0.5, wooden, steel, or concrete ties should be used to restrain the ceilings.

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3.1.4.8.3 Connections of building components The following should be monitored in evaluating the connections of building components. • Connections between load-bearing cross walls. • Connections between load-bearing walls and ceiling. • Connections between walls and ceiling perpendicular to the wall plate. • Connections between blades and load-bearing walls. 3.1.4.8.3.1 Connections between load-bearing crossed walls

The following conditions must be observed to control the connection between the crossed walls. • All masonry units in all load-bearing crossed walls must be arranged in an aligned level. • All masonry units in all load-bearing crossed walls must be raised to one level. • Crossed walls must be executed at the same time, or in case they are not executed, using racking back is permitted. In executing the walls, concrete, steel, and wooden corner ties must not be used. 3.1.4.8.3.2 Connection between load-bearing walls and ceiling

The conditions in the following are necessary to follow to control the connection between load-bearing walls and ceiling. In addition, in concrete reinforced ceilings casted-in place implementing horizontal ties is not necessary. • Masonry material load-bearing walls must be braced (restrained) by using appropriate braces in floor level so that the earthquake force is transformed to load-bearing walls without ceiling displacement. 3.1.4.8.3.3 Connection between walls and ceiling perpendicular to wall plate

To transfer forces perpendicular to wall plate to the ceiling, the connection between wall and ceiling must be able to tolerate the force perpendicular to the wall plate. 3.1.4.8.3.4 Connection between nonstructural wall (partition) and loadbearing walls

There must be arranged simultaneously or in racking back form, or toothing.

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3.1.4.8.4 Evaluating ties components in masonry building The following should be monitored when evaluating building ties. • Evaluating the existence of horizontal foundation ties. • Quality assessment of concrete ties materials. • Evaluation of connection of ties. • Evaluation of the ties system through detachment. • Evaluation of ties through passing pipe. • Evaluation of wall connection and ties. • Evaluating the dimensions of ties. 3.1.4.8.4.1 Evaluating the existence of horizontal foundation ties

The following conditions must be observed to evaluate the existence of horizontal foundation ties. • In the foundation alignment, horizontal foundation ties must be used. • Foundations, and also through consistency, can play the role of horizontal ties. 3.1.4.8.4.2 Quality evaluation of concrete ties materials

The following conditions must be monitored to evaluate quality of concrete ties materials. • No pores or other defects in the concrete must be observed during inspection of ties. • The minimum compression strength of concrete is 150 kg/cm2. 3.1.4.8.4.3 Evaluation of connection of ties

The following conditions must be observed to evaluate the connections of the components of the ties. • Reinforced concrete tie bars shall have the necessary overlap in connections. • Connections of steel ties should be suitable. 3.1.4.8.4.4 Evaluation of the ties system through detachment

The following conditions must be observed for the evaluation of the ties system by the existence through detachment. • The presence of an opening or a half-floor should not cut horizontal or vertical ties at any level of the building. • Vertical or horizontal ties should be connected to adjacent ties.

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3.1.4.8.4.5 Evaluation of ties through passing pipe

The following conditions must be observed for the evaluation of the ties through passing pipe. • Water, sewer, or chimney pipes should not cross horizontal or vertical ties. • If the first criterion is not met, the detachable diameter shall not exceed 1.8 width of tie. 3.1.4.8.4.6 Evaluation of wall connection and ties

A proper connection between the wall and the coil must be established. 3.1.4.8.4.7 Ties dimension

Ties should be made to the width of the walls and the height and width of the ties should not be less than 20 cm.

3.1.5 Generalities for masonry infill wall in frames such as concrete or steel frame 3.1.5.1 What is a masonry infill wall? Building frames filled with masonry walls are called short-lived frames. Intermediate frame materials may be brick, concrete, earthenware, hemp, etc., also called infill. Research shows that infill frames significantly increase the stiffness, strength, and change in ductility of structures compared to infill frames. This effect may have a favorable or adverse effect on the seismic behavior of structures. The infill effects are one of the most important clauses in the calculation period of structure in which unfortunately, engineers have doubts about in many cases. In addition, this leads to the error in the calculation of period which strongly influences the design of the structure [1
3] (Fig. 3.1.28). Unfortunately, for design and analysis, steel and concrete buildings are only considered as frames consisting of main members such as beams, columns, and braces. In this case, masonry infill frames are seen as external and internal walls in common urban buildings. These buildings are made of a concrete or steel load-bearing structure in which infill frames are used as separators of architectural spaces and also as covering walls, to fill structure frames. In this situation, their behavior is not similar to empty frames. These walls are called infill frames and the resulted frame from combining

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Figure 3.1.28 Infill destruction caused by the earthquake in a building.

frame and infill frame is called composite frame. However, in designing structure with frames, infill frames are considered as nonstructural elements and modeling for these elements is neglected. Looking at past earthquakes in Iran In many cases, the brick walls of the frames have significantly improved the performance of structures during earthquakes, most of which can be seen in traditional buildings without a coherent seismic load-bearing system. For example, the positive and effective performance of infill frames in Iran-Manjil earthquake of 1969 can be mentioned. Most of the structures in this area had beam-to-column joints and only infill frames played a lateral load-bearing role, with many of these structures being medium or short with no collapse during earthquake which is only due to infill frames although infill frames were cracked during under earthquake force.

3.1.5.2 Problems of neglecting infill effective of frames stiffness Usually due to neglecting the hardening effect of infill frames which increases stiffness of frames significantly, lots of damages occur to composite frames. The reason is that an increase in stiffness leads to the decrease in period of composite frame in comparison to empty frame which attracts more earthquake force, leading to high stress effects on infill frames and consequently small or complete failures in fill frames. As a result of the overall failure of the enclosures, the high force previously tolerated by the composite frame is abruptly applied to the lean members (beams and columns) of the frame as they have never been analyzed and designed for such force. These components are severely damaged and endanger stability the frame (Table 3.1.10).

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Table 3.1.10 Effects of brick infills on structures. Row Negative effects

1

Irregularity of stiffness in height (soft floor)

2 3 4

Irregularity of strength in height (weak floor) Irregularity of stiffness in plan (torsion) Inappropriate distribution of force between columns of a concrete frame (Short concrete column) Inappropriate distribution of force in plan (short steel column) Increasing design force due to lack of period

5 6 7

• • • •

Increasing design force due to the decrease in behavior factor of compound system

Positive effects

Increasing stiffness and decreasing displacement Increasing strength Decreasing ductility Increasing basic level in special conditions Ductile shear failure in short steel column Frame design for small lateral force Creating hybrid system with axial action frame

Increase in the force applied to connections. Short column phenomenon as a result of executing thick walls between columns with a height less than floor height. Creating torsion in the building due to uneven distribution and irregularity in internal walls. Decrease in strength-to-weight ratio [1].

3.1.5.3 What is the condition of wall for infill performance? A wall acts as an infill when it contributes to the stiffness and lateral resistance of the building and meets all of the following conditions: • Having enough on-plate perpendicular strength. • Mortar in the bound brickwork are made of cement or lime cement mortar and lime hydrated mortar are not accepted. • There is no distance between the wall and frame members and the wall is in full contact with beams and columns. • Perpendicular bound of the wall have mortar or they are appropriately filled with new mortar. • The wall must not have diagonal cracks with width more than 3 mm. Additionally, there must not be tracks due to soil subsidence. • Bricks in the wall which provides lateral strength of structure must be in form of toothing so that each upper brake covers at least 0.25% of the lower brake. • There must be no protrusion or bending in the wall.

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•

235

The height and length of the wall must be less than 4 and 6 m, respectively.

3.1.5.4 How can an infill frame create a soft story in the building’s structure? Many believe that infill frames have a positive effect on the final stiffness and stiffness of the structure. Infill frames can make the first soft floor by temporarily making floors harder in the structure because of the earthquake as soon as capacity is lost, the stiffness in that floor is greatly reduced, which is extremely undesirable for seismic performance, and it creates a soft floor.

3.1.5.5 How is the interaction between frames and infill frames formed in compound frames? Although the behavior of the frame is often bending and the wall behavior is shear, the interaction of the frame and the infill frame changes the mechanism of strength. In other words, the infill frame prevents free movement of the frame and as a result of this interaction the power transfer from the bending method to the empty frame is converted to the truss in the composite frame. Force transfer with truss method increases axial forces and decreases bending anchors and shear forces in frame columns (Fig. 3.1.29).

3.1.5.6 Distribution of stress in fill frame The plate stresses created inside the frame by the lateral force applied to the frame are such that the maximum tensile stress occurs in the infill frame center and the maximum compressive stress along the compressive diameter at the edge of the frame. The average tensile stress on the tensile diameter is much lower than the average tensile stress on the compressive

Figure 3.1.29 The difference between buildings with or without masonry infills.

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Seismic Rehabilitation Methods for Existing Buildings

diameter, thus the increase the tensile diameter is much less than the reduction in the compressive length. Professor Moghaddam and Stafford Smith have concluded in their research that the more the frame is stiffer than the frame, the longer the frame relies on the infill frame, and therefore, the longer the contact length between them, the more interactive the forces are distributed over the wider surface, and the stresses on the infill frame are lowered at the corners, while the center stresses of the frame are independent of the stiffness of the frame and depend only on the aspect ratio of the frame.

3.1.5.7 Which bylaws are used in the scope of this book to evaluate brick walls? In this book, the requirements of Code.No. 360 and FEMA 356 are used to evaluate and analyze the infill frames.

3.1.5.8 What is the mechanism of action of infill frames against earthquake force in target displacement? The mechanism of action of infill frames during target displacement of forces coincides with the successive failure modes in the force diagram and displacement. These failure modes in composite frames are in the following. 3.1.5.8.1 Border crack This mode is one of the main features of composite frames and usually occurs in the early stages. This mode causes the geometrical deformation of the frame so that one of its diameters becomes shorter and the other diameter becomes longer. The force is increased at a compressive diameter to cause a failure. 3.1.5.8.2 Corner crushing mode In this case at least one corner under the infill frame pressure is crushed. This mode is strongly affected by the relative stiffness of the frame and the infill frame. Relatively strong frames focus too much compressive stress on the center of the infill frame, which results in the failure mode of the diagonal crack, whereas in the weak frames the angular stresses propagate only in a small area, causing the fracture and crushing modes of the corner. According to Redington finite element analysis results, the dimensional ratio of the infill frame (h/L) has no effect on the angle of failure

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237

and crushing of corners except in the case of very high infill frames where the stresses on angles are very high. 3.1.5.8.3 Sliding shear failure mode In this case, sliding shear failure occurs between the horizontal seams of the infill frames and usually occurs in strong frames with weak mortar between the seams. This mode is usually the case for higher aspect ratio infill frames (h/L). 3.1.5.8.4 The diagonal or tensile diagonal cracking mode In this case, a diagonal crack is formed along a pressure diameter from corner to corner. In infill frames with very strong mortar, the mortar prevents the cracks from passing through the horizontal and vertical seams, the diagonal fracture being tensile; whereas in the conventional mortar infill frames, the diagonal crack does not pass through the bricks but passes through the horizontal and vertical mortar. This failure is shear type. This mode is affected by the tensile strength between the frame and the aspect ratio of the infill frame (h/L). The results of analyzes and measurements show the highest tensile stress in the center of the infill frame. In addition, the analytical results of Redington and Benjamin and Williams show that the ultimate bearing capacity decreases with increasing aspect ratio (h/L). This mode should not be considered as a failure mode because the frame is still able to withstand further loads after the crack is created. 3.1.5.8.5 Diagonal compression failure mode In this case, the infill frame crumbles in its central region, which usually occurs in composite frames with lean off-plate infill frames. Of course, this mode rarely happens because off-plate buckling of the infill frame requires a high slimming ratio, which due to the size of the panels and their high thickness, this ratio cannot be satisfied (Fig. 3.1.30). 3.1.5.8.6 Shear failure in column This is caused by the combination of shear forces (which the infill frame applies into the frame) and the tensile force (resulting from the frame's function) in the column near the compressive corner of the frame. This phenomenon is most commonly seen in concrete columns, which are often designed for compressive loads and do not occur in steel frames due to their high tensile strength.

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3.1.5.8.7 Short column break In some buildings due to architectural constraints such as the openings, the thick walls that fill the columns are less than the height of the floor. The high stiffness of these walls causes the location of the critical cut-off point of the column to be changed, and since no special arrangements such as reducing the distance stirrups at this point are not considered, the columns are vulnerable at these points (Fig. 3.1.31). The general principle of seismic rehabilitation of composite frames is to determine the layout of the infill within the frame. This combination is divided into two main types: the first type of frame-based infills whose performance is like an infill with shear behavior that generally requires improvement. The second type of infills, which is not completely enclosed within the frame, performs better in steel structures, and each of these infills should be evaluated differently with respect to their different behavior in arrangements against displacement.

Figure 3.1.30 Types of modes failure in the masonry infills.

Figure 3.1.31 Seismic behavior analysis in building.

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Types of existing buildings: detailed introduction and seismic rehabilitation

3.1.5.9 Examine methods for analyzing of frames with brick walls Evaluation material of infill buildings involves analysis and evaluation in both in-plane and perpendicular behavior. In each of the above cases, the stiffness, strength, and acceptance criteria must be considered. Calculate the stiffness and strength for in-plane evaluation in one of two ways (Fig. 3.1.32). 3.1.5.9.1 First step In this section before introducing the methods of analysis and evaluation of stiffness and strength of infills, the necessary information about the physical properties of the infill’s material should be obtained. In this case, according to the presented materials in sampling and digging section the extracted parameters from seismic rehabilitation projects are briefly introduced in the form of three effective parameters in seismic rehabilitation of infills of masonry materials in composite frame. These parameters are: • Compressive strength of the existing masonry materials. • Tensile strength in flexural (bending). • Shear strength of used mortar in masonry materials. • The expected elastic modulus. • The expected shear modulus (Fig. 3.1.33). 3.1.5.9.1.1 Compressive strength of the existing masonry materials f 0me

According to the results of experiments on projects, the cement block walls enjoy laboratory compressive strength (f 0me ) of about 50
100 kg/cm2 and in brick walls the abovementioned strength is about 50
200 kg/cm2. The following equation is used to calculate the expected compressive strength of the masonry materials. fme 5 1:3f 0m

Figure 3.1.32 Structure frame with infill wall.

(3.1.17)

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Figure 3.1.33 The displacement and force curve for a simple frame and a infill frame.

3.1.5.9.1.2 Tensile strength in bending fr

Tensile pffiffiffiffiffistrength in bending for infill materials is calculated through α 3 f 0m that is in buildings with brick infills α 5 0:63 and in buildings with cement block infills α 5 0:52. 3.1.5.9.1.3 The expected shearing strength Vme

The method of determining the expected shearing strength of masonry materials is shown in (Section 3.1.4.6.3.1.3.1). 3.1.5.9.1.4 The expected elastic constant Eme

The expected elastic constant of an infill with masonry material equals to the expected compressive strength of masonry material multiplied by 550. 3.1.5.9.1.5 The expected shear modulus Gme

The expected shear modulus of an infill with masonry material is equivalent to 40% of the expected elastic constant of the infill. Generally, the behavior of infill is derived from the strength of the existing frame and partition materials to: • Stiffness and high toughness. • Increased earthquake force on buildings. • The interaction between the frame and the diagonal improves the behavior. • The interaction between the frame and the diagonal improves the behavior. • Maximum tensile tension along the traction diameter and in the center of the infill frame. • Diameter compressive tension in frame corner; (Fig. 3.1.34).

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241

3.1.5.9.2 Analysis method In general, the analysis and evaluation methods discussed in this chapter are based on the applied methods of linear and nonlinear static procedures. In the concepts of stiffness and strength section, linear and nonlinear procedures are presented simultaneously so that the reader can better understand the content of the analysis. Modeling is performed in the infill for analysis in the form of macro models and micro models (Fig. 3.1.35). 1. Method of using equivalent diameter components In this method, the components of aggregate are evaluated by considering the criteria in the form of diagonal components alongside the components of the aggregate as a set of two types of elastic and nonelastic behavior. 2. Nonlinear finite element method In this section before introducing the analysis and method of evaluation of hardness and strength in the infill frames, the necessary information about the physical properties of the infill materials must be obtained. 3.1.5.9.3 How to evaluate of masonry infill wall? According to Fig. 3.1.36, infill wall must be thoroughly evaluated for both in-plane and out-plane modes (Fig. 3.1.37).

Figure 3.1.34 How to distribute earthquake force in infill wall and frame.

Figure 3.1.35 Chart of modeling the infill frame and wall.

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Seismic Rehabilitation Methods for Existing Buildings

Figure 3.1.36 Chart of evaluation of masonry infill wall.

Figure 3.1.37 On-plane deformations of walls.

3.1.5.9.3.1 Evaluate of masonry infill wall

Evaluation of infill wall including calculation of stiffness and strength must be defined in two methods. These methods are equivalent linear element method and nonlinear finite element method. In equivalent linear elements method, the infill wall with linear elements next to the frame elements as a set is considered to have both elastic and inelastic behavior. In nonlinear finite element method, the frame and the infill wall are considered as a composite frame considering the openings and the cracking of the infill wall as a result of the loads [1,2]. 3.1.5.9.3.1.1 Frame collapse mode In this case, the columns or beam connections to the dough joint are created. This mode usually occurs in weak frames or frames with weak connections with strong members and relatively strong infill frames. This mode occurs only in composite concrete frames. Generally, steel joints are broken in this case. In most common steel joints, the upper and lower two angles are used for joining beams to columns. Generally, transfer of gravity loads of welding A is done by the main welding and gravity loads of welding B is done by subwelding (point weld). However, during an earthquake, large forces are

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243

created in the infill frame. These forces can have large upward component and in many cases can overcome the weight force applied to joints and break the angle. In-plane elastic stiffness of an infill is achieved by making the features equivalent by an equivalent diagonal compressive brace, thus each wall is replaced by a diagonal structural member or a (CBF) brace and then structure is analyzed and evaluated (Fig. 3.1.38). Assessment of a building frame with an infill is not permitted without modeling diagonal braces—parallel infills. Also, the calculation of the stiffness of the walls parallel with the earthquake force surrounding the infill can be done using finite element methods or divided components of infill but the following is a simpler way of determining the stiffness according to the criteria presented in the existing 360 seismic recipe instruction and FEMA 356 [1
3]. 3.1.5.9.3.1.2 Stiffness of masonry infill Basic assumptions for determining the stiffness of infill. When applying earthquake forces due to the deformation of the frame, as can be seen, the infill tends to be uplift at points 1 and 2. And tangential compressive stress is produced at points 3 and 4. Correct recognition of this behavior suggests that we need to design new components with infill specification for participation of infill stiffness. 3.1.5.9.3.1.2.1 Determining infill stiffness within the range of linear behavior of materials

Infill The elastic stiffness within the wall of the perimeter wall between the infill building materials before cracking shall be determined by applying a pressure gauge equivalent to a width using the calculation and modeling equations. Also, the thickness and elasticity of the compression wrench (CBF brace) should be the same as the infill studied [2] (Table 3.1.11; Fig. 3.1.39).

Figure 3.1.38 Modeling infill with brace system.

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Table 3.1.11 Parameters using for calculation stiffness of infill wall. Row Parameters Description

1 2 3 4 5 6 7

hcol hinf Efe Eme Icol rinf tinf

8

θ

9

λ1

Center height to center of column: cm Height of infill panel: cm Expected elasticity coefficient of frame materials: — Expected elasticity coefficient of infill materials: kg=cm2 Anchor inertia column: cm4 Diameter of infill frames panel: cm The thickness of the infill frames panel and the equivalent pressure gauge: cm An angle whose tangent is equal to the panel's ratio (height to length ratio) The coefficient used to calculate the width equivalent to the panel pressure gauge

Figure 3.1.39 Equation of infill wall to brace and then calculate infill wall stiffness.

w 5 0:254½λ1 hcol  rinf 0:4

  10Eme tinf sin2θ 0:25 λ1 5 Efe Icol hinf

(3.1.18)

The stiffness of unmarked cracked masonry infill frames is obtained analytically by considering the nonlinear behavior of the infill system after masonry cracking. Infill with opening area Evaluation of these types of infills is generally done in the following way in seismic rehabilitation (Fig. 3.1.40). • The macro modeling is presented in FEMA 356 bylaw for opening infill frames. For infill with opening the Winf must be added by α.this parameter is the effective coefficient of reduction of the effective width of the diameter

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constraints. In this method, if the opening area is more than 60% of the infill area, the effect of the infill is ignored (Table 3.1.12). Wmod 5 αWinf  2   A0 A0 α 5 0:6 2 1:6 11 AP AP

(3.1.19) (3.1.20)

3.1.5.9.3.1.2.2 Determining infill stiffness within nonlinear behavior range of materials The infill stiffness within the nonlinear behavior range of mate-

rials is modeled such that the sheer force of the infill is equal to that of the plan of compressive force in equivalent brace. In this case, the ductility capacity of masonry materials’ infill is only a function of the parameter d. In such infills the maximum permissible displacement is 1.5%, thus performance level of life safety for the system is achieved. It worth to mention that there must be a complete confinement, otherwise as the applying of the force continues and deformation increases, the infill is thrown out of the frame [1
3] (Table 3.1.13; Fig. 3.1.41).

Figure 3.1.40 Equation of infill wall with opening area to brace and then calculate infill wall stiffness. Table 3.1.12 Parameters using for calculation stiffness of infill wall with opening area. Row Parameters Description

1 2 3

α A0 AP

Decrease coefficient Infill area Opening area

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Table 3.1.13 Define β Parameters for nonlinear analysis of infill wall. Row β 5 ðVframe =VInfill Þ Linf =hinf %d

1 2 3

β , 0:7 0:7 # β , 1:3 β $ 1:3

0.5 0.5 0.5

1.0 1.0 1.0

2.0 2.0 2.0

0.5 1.0 1.5

0.4 0.8 1.2

0.3 0.6 0.9

Figure 3.1.41 Diagram of force and displacement in masonry infill wall.

In the static linear method, the stiffness of Ke is calculated for the infill, without considering the effect of the gravity loads on the lateral deformation of Kp in the nonlinear phase equal to 0
0.1 equivalent stiffness in the linear phase. 3.1.5.9.3.1.3 Strength of masonry infill 3.1.5.9.3.1.3.1 Sliding shear strength Prior to slip failure in building materials’ infill frames, the equivalent structural mechanism is the diabetic fiberreinforced slab, in which case the slit is tolerated on the infill by the composite frames. The structure changes to the restrained frame at an equivalent angle. In this case, the support created by the crossbars cause’s dough joints to form in the middle and above or below the height of the columns or to result in shear failure of the column. In this situation, a large percentage of this section is transferred to the columns, causing additional anchorages and extra sections in the column. The maximum shear force tolerated by the infill is [1
3]:

H 5 Fd cosθ 5

Linf dinf

(3.1.21) H 5 τ 0 Linf tinf 1 μ Fd sinθ   hinf hcol τ0

dinf tinf Fd D -Fd 5 Linf Lbeam col 1 2 μ Lhbeam (3.1.22)

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On average, shear strength in brick-walled infill frames is: Fd 5

0:03f 0m dinf Utinf col 1 2 0:3 lhbeam

(3.1.23)

The shear force required to slip into the multi-span frames in the first step is (Fig. 3.1.42): n X Vb 5 ðFdi cosθi Þ

(3.1.24)

i51

As mentioned, after the slip, the shear forces of the columns’ infill frames and beams inserted into the frame contribute to the shear force. Therefore the shear fracture load of the frame is obtained from the following relation: V5

n11 X 2 ðMct 1MCC Þi 1 Vb h i51 e

(3.1.25)

hcol 2

(3.1.26)

he D

3.1.5.9.3.1.3.2 Corner failure strength The fracture strength of the corner is

obtained from the following equation, which is discussed in terms of the three equations under the equilibrium coefficient corresponding to the type of fracture η in each of the states. H 5 η:f 0m :tinf :hinf

Figure 3.1.42 Sliding shear strength for infill frame.

(3.1.27)

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Case I In this case the infill is weak and the plastic connection is formed at the end nodes and the corner strength is extracted from the following relation: η5

f

4MPJ 0 :t :h2 m inf inf

1

1 6

(3.1.28)

Case II In this case the beam is weaker than the columns, but a strong infill plastic connection is formed in the beams and the shear strength of the beam is extracted from the following relation:  sffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi 2ðMPJ 1 MPb Þ 1 hinf η5 -tanθ 5 (3.1.29) 2 0 tan θ f m :tinf :hinf Linf Case III In this case, the columns are weaker than the beams, but a strong plastic connection is formed in the columns and the shear strength of the corner is extracted from the following relation: sffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi 2ðMPJ 1 MPC Þ hinf η5 -tanθ 5 (3.1.30) 2 0 f m :tinf :hinf Linf 3.1.5.9.3.1.3.3 Determination of interfacial strength in linear and nonlinear behavior range of materials The behavior of the ambient infill is in a

deformation controlled. The expected shear strength inside the infill plate can be determined using the following equations. The following relation can also be used to determine the shear strength of the mortar (Table 3.1.14). QCE 5 Vine -Vine 5 Ani fvie mkQCE 5 mkVine 5 mkAni fvie $ QUD 5 VUD

(3.1.31) (3.1.32)

Table 3.1.14 Define Parameters for strength calculation of infill wall. Row Parameter Description

1

Ani

2 3 4

fvie Vine Vt

Pure horizontal cross-sectional area between two adjacent rows of infill frames panel Expected shear strength of infill building materials fvie # 0:35Vt Expected shear strength of the infill Shear strength of mortar

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3.1.5.9.3.1.3.4 Acceptance criteria To assess acceptance criteria in an infill,

all components of the infill must be thoroughly assessed, analyzed, and evaluated for acceptance criterion. In this case, each of the following in the composite frame must be thoroughly investigated (Fig. 3.1.43). Columns Analysis of Vme of an infill for acceptance criteria for columns is as follows (Table 3.1.15; Fig. 3.1.44): The expected flexural and shear strength of columns adjacent to the infill should be at least equal to the larger of the two forces in the following: 1. Applying the expected horizontal component force of infill’s equivalent brace, modeled brace (CBF), with the distance of lCeff from the top or bottom of the infill panel on the adjacent column. tan θC 5

a hinf 2 cosθ C

Linf

-lCeff 5

a cosθC

(3.1.33)

Note: In this case, the columns are assumed to be rigid-end.

Figure 3.1.43 Dividing the frame into the main elements in the frames with masonry infill. Table 3.1.15 Deciding whether to apply Vme effects in computing. Row Vme Infill performance Columns analysis

1

# 1.4

2

5 1.4

3

$ 1.4

The frame is matched by its various courses and does not exert additional force on its adjacent columns. It exerts additional force on its adjacent columns. It exerts additional force on its adjacent columns.

no need to examine the interaction between the infill and the frame The interaction between the infill and the frame needs to be examined

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Figure 3.1.44 Columns acceptance criteria shape.

2. The shear force resulting from developing expected bending strength of the column above and below the effective column length ensures that the columns are articulated in this criterion. VCE 5

2MCE ðhinf 2 lC:eff Þ

(3.1.34)

Note: When the columns are surrounded by short infills, the effective length of the column is reduced and is equal to the height of the opening. Beams The control of the beams in the infill's frame must first be modeled under forces obtained from the analysis of the structure (with CBF brace) in accordance with similar beams and the strength evaluation must be double-checked (Fig. 3.1.45). Also, if the expected shear strength of the masonry materials Vt is less than 3.5 kg/cm2, no control of the effect of the infill force on the adjacent beams is needed. The bending and shear strength adjacent to a frame with infill must be at least equal to the largest force obtained from the followings: 1. Applying the expected vertical component of infill’s compressive brace at the length of lbeff from top or bottom of the infill panel that is imposed from infill into the beams adjacent to the frame. tan θb 5

hinf a a -lb:eff 5 sinθb Linf 2 sinθC

(3.1.35)

Note: In this case, the beams are assumed to be fixed-end. The shear force resulting from developing expected bending strength of the beam at the both end of the effective beam length ensures that the beams are articulated in this criterion. VCE 5

2MCE ðhinf 2 lb:eff Þ

(3.1.36)

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251

Figure 3.1.45 Beams acceptance criteria shape.

Acceptance criteria for column in linear and dynamic static analysis method For columns modeled as compression or tension members, the values of the designer responses are extracted from Tables 3.1.16 and 3.1.17 (Figs. 3.1.46 and 3.1.47). Control of infill in the linear behavior Using linear procedures, the internal stress of controlled masonry materials infills are taken into account by deformation. In infill evaluation, the shearing force in parallel infills resulted from earthquake and horizontal (plan) compressive forces of modeled diagonal bracket are evaluated. In this range of analysis, modification factor of the nonlinear behavior of m number of members is extracted using Tables 3.1.18 and 3.1.19 (Fig. 3.1.48). QCE 5 Vine 5 Ani fvie QUD # 1-mkQCE 5 mkVinf 5 m:k:Ainf :fVinf mkQCE   21 hinf QUD 5 F:cosθ-θ 5 tan linf

(3.1.37) (3.1.38) (3.1.39)

Infill control within the range of nonlinear behavior Table 3.1.20 is used for nonlinear evaluation of infills within the nonlinear behavior range. Using the simplified force
displacement equations for masonry materials’ infill in nonlinear static procedure, LS is presented in the following table. 0:02 # LS # 0:011.

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Table 3.1.16 m factor for column acceptance criteria on infill frame. Conditions

m coefficients Performance level IO

Member type Primary

Columns modeled as pressure bars Columns enclosed full length Other condition Columns modeled as tensile bars Nonpatched columns or properly enclosed patches Other condition

Secondary

LS

CP

LS

CP

1 1

3 1

4 1

4 1

5 1

3 1

4 2

5 2

5 3

6 4

This value is usually varying from 0.02 to 0.025 for infills. In this case, in this case, the frames are too rigid to restrained seismic load. Acceptance criteria in static and dynamic linear methods The primary members of the deformation-controlled responses are the bending and axial modes of the beams, slabs and columns as well as lateral deformation in the response to infill frames. In nonconnection members, deformation-controlled behaviors include beam and column bending, and in the case of infill frames in accordance with the infill type. All other responses are considered to be force controlled. Responses and design efforts in the members must be determined in accordance with the requirements of the linear analysis method. One of the important parameters of extraction in evaluations is the demand-capacity-ratio, which in the text of this chapter is called DCR. If the following principles are DCR . 1 the following factors must be specified on the limit analysis: • anchors, sections, torsional anchors; • attachment and patch responses (corresponding to the strength required to reach the member); • joints sections (corresponding to the beam and column connectivity required at the strength level); and • axial forces in columns and joints (corresponding to possible paste performance for upper class members). If the following is achieved in one level of the building, that floor is considered to have a poorly loaded lateral load system. DCRave:col . DCRave;beam -DCRave:col . 1-DCRave:col . 0:5mave:col . In this case one of the following conditions must be met: • All key members as well as non-key members in the relevant level should be included in the modeling and moderated DCR requalification.

Table 3.1.17 Modeling parameters and acceptance criteria for nonlinear analysis infill frames. Conditions Modeling parameters Acceptance criteria Pulp angle, radians

Residual strength ratio

Performance level IO

Member type Primary

a

b

c

0.02 0.003

0.04 0.01

0.4 0.2

0.05

0.05

See note

0.03

Secondary

LS

CP

LS

CP

0.003 0.002

0.015 0.002

0.020 0.003

0.03 0.01

0.04 0.01

0.0

0.01

0.03

0.04

0.04

0.05

0.2

note

0.02

0.03

0.03

0.2

Columns modeled as pressure rods

Columns enclosed full-length Other condition Columns modeled as tensile bars

Nonpatched columns or properly enclosed patches Other condition

Note: Potential for splice failure shall be evaluated directly to determine the modeling and acceptability criteria. For these cases, refer to the generalized procedure of concrete subchapter (3.2). For primary actions, collapse prevention performance level shall be defined as the deformation at which strength degradation begins. Life safety performance level shall be taken as three-quarters of that value [3].

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Figure 3.1.46 The behavior of the columns in the boundary area of the masonry infills.

Figure 3.1.47 The behavior of the beams in the boundary area of the masonry infills. Table 3.1.18 Parameters to control of infill in the linear behavior. Row Parameter Description

1

Ani

2 3 4 5 6

fvie Vine Vt QUD QCE

Horizontal net cross section of mortar between two courses adjacent to infill’s panel Expected shear strength of masonry material’s infill Expected shear strength of infill Shear strength of mortar Horizontal component of diagonal braces compressive force Shear strength of infill

Table 3.1.19 Infill control parameters in linear methods. β 5 Vframe =VInfill Linf =hinf m IO

β , 0:7 0:7 # β , 1:3 β . 1:3

0.5 0.5 0.5

1.0 1.0 1.0

2.0 2.0 2.0

1.0 1.5 1.5

LS

1.0 1.2 1.2

1.0 1.0 1.0

4.0 6.0 8.0

CP

3.5 5.2 7.0

3.0 4.5 6.0

— — —

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Figure 3.1.48 Masonry infill acceptance criteria shape.

Table 3.1.20 Infill control parameters in nonlinear methods. β 5 Vframe =VInfill Linf =hinf %d

β , 0:7 0:7 # β , 1:3 β . 1:3

0.5 0.5 0.5

1.0 1.0 1.0

2.0 2.0 2.0

0.5 1.0 1.5

0.4 0.8 1.2

0.3 0.6 0.9

Acceptance critic a LS%

0.4 0.8 1.1

0.3 0.6 0.9

0.2 0.4 0.7

If the average DCR value for the vertical component is greater than the horizontal component and its value is greater than 2, the building should be re-analyzed in a nonlinear way and appropriately reconstructed so that its defects can be completely eliminated. • The building should be re-analyzed by static or nonlinear dynamic methods. • The building should be renovated in such a way that the defect of the weak floor is eliminated. Evaluation of masonry materials infills, perpendicular to the surface Normal bending interaction In on-plate projectile mode in infill frame, two longitudinal components (in infill frame plate) and latitudinal (perpendicular to infill frame) are simultaneously applied to the infill frame (Fig. 3.1.49). As a result of crumbling, the capability of arch action of the infill frame which is the most important factor to maintain infill frame statics against earthquake forces is decreased dramatically. There is an interaction among infill frame failure modes as a result of plate and latitudinal forces.

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Therefore displacement of the composite frame must be limited so that transverse strength needed for statics against earthquake is provided. Otherwise, infill frame is projected out of the frame, and strength and stiffness of the structure is extremely changed, thus putting seismic statics at risk. Infill capacity in expanding the internal compressive forces when loaded in a perpendicular direction to the infill plate is called the normal bending interaction of the wall. Also, if the infill is capable of inducing arc action, the internal compressive stress capacity of the infill will increase [1
3] (Figs. 3.1.50 and 3.1.51). When can take normal bending interaction effective into account in an infill?

Figure 3.1.49 Wall deformation shape for on-plane force.

Figure 3.1.50 The earthquake forces the wall off its plate.

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1. All of the masonry materials’ infill should be in full contact with the frame. 2. Flexural stiffness of all beams and columns of the frames should be greater than 1 3 1010 kg=cm2 . It means it mustn’t be flexible at end. 3. ðhinf =tinf Þ 5 25. Masonry materials’ infill with ðhinf =tinf Þ ratio of less than given values in following table are not needed to be evaluated against the earthquake forces perpendicular to the plane. Maximum ratios of ðhinf =tinf Þ (Table 3.1.21). Stiffness • The stiffness perpendicular to the plan of the frame is not taken into account as perpendicular in the overall structure modeling. • Flexural stiffness of unbroken masonry materials infills under perpendicular lateral forces shall be determined on the basis of the minimum net cross section of the mortar in addition to cementation on the wall. • Flexural stiffness of cracked panels of masonry infill under forces perpendicular to the plane shall be assumed to be 0.

Figure 3.1.51 Position of the infill at maximum perpendicular displacement to the plane. (A) Interaction is present: working stress is large. (B) Interaction is not present: working stress is small. Note: To create the arc action, the situation presented in figure a must exists in both the horizontal and the vertical walls.

Table 3.1.21 Masonry materials’ infill with ðhinf =tinf Þ ratio. Performance level Low seismic zone Moderate seismic zone High seismic zone

IO LS CP

14 15 16

13 14 15

8 9 10

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Note: If there is an interaction, the flexural stiffness of the cracked member should be taken into account. Also relative displacement in nonlinear analysis is required (Table 3.1.22). h i hinf 0:002 tinf Δinf rffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi 5 (3.1.40) h i2ffi hinf hinf 1 1 1 2 0:002 tinf Strength 1. Noninteraction The tolerable force of infill (qin ) in the direction perpendicular to the plane is equal to the cracking moment of the cross section (Table 3.1.23). 24MCr A pffiffiffiffiffiffiffiffiffiffi 2 α f 0 tinf MCr 5 6 8sffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi 92  2 <  2 = hinf linf 2 A 5 hinf 113 21 ; tinf : tinf qin 5

(3.1.41) (3.1.42)

(3.1.43)

2. Existence of interaction The tolerable force of infill qin in the direction perpendicular to the plane is greater than the cracking moment of the cross section. Also the lower bound of the strength which is perpendicular to the plane is obtained from the following equation (Table 3.1.24): 0:7 f 0m λ2 :144 QCL 5 qin 5  hinf =tinf

(3.1.44)

Table 3.1.22 Parameter for control flexural stiffness conditions of masonry infill.

Δinf hinf

Displacement of infill’s midpoint in a direction perpendicular to its plane Infill wall’s height

Table 3.1.23 Parameter for control strength of masonry infill.

α (brick wall) α (block wall) MCr

0.63 0.53 Cracking moment of 1-cm cross section

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259

Acceptance criteria

Acceptance criteria within the linear behavior rangeThe acceptance and analysis criteria are in a way that tolerable force for the infill, in case of being perpendicular to the plate, must not be smaller than Fp which is design load to brace the walls (Table 3.1.25). qin $ FP -FP 5 β 3 Ss 3 W

(3.1.45)

Acceptance criteria in nonlinear procedureIn this method, performance level for uninterrupted usability, life safety, and collapse threshold of the structure, the ratio of displacement perpendicular to the infill plate to the height under force of Fp must not be greater than 2%, 3%, and 5%, respectively. Conclusion Buildings are generally made of a reinforced concrete or steel load-bearing structure in which infill frames, as separators of architectural spaces and also covering walls, have filled the space between frames of the structure. In this case, their behaviors are not the same as the empty frames. Infill frames affect strength, stiffness, and ductility of composite frames. However, they are still considered as nonstructural elements in common designs of structures with frames and they are not modeled. Infill frames change the behavior of the building as a result of lateral forces such as wind and earthquake. When average or strong earthquakes erupt, masonry infill frames collide into the surrounding frame and interaction forces are created between them. These forces

Table 3.1.24 λ2 parameters define in existence of interaction.

λ2

hinf λ2

5 0.129

10 0.060

15 0.034

25 0.013

Table 3.1.25 Acceptance criteria within the linear behavior range.

Ss W β

Spectral response acceleration at short period for selective earthquake level and damping of 5% (Weight of unit infill wall)

Collapse prevention

Life safety

Immediate occupancy

0.6

0.4

0.3

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increase load-bearing capacity and stiffness of composite frame. Larger damage to composite frames is usually caused by ignoring the hardening effect between the frames, which sometimes increase the stiffness of the frames up to several times. This increase in stiffness causes a decrease in composite frame period in comparison to empty frames, thus more earthquake forces are attracted and infill frames are therefore are affected by high stresses. The increase in stresses leads to small or complete failure of frames. As a result of complete failure of infill frames, the high force that was tolerated by the composite frame is suddenly applied to thin elements of frame (columns and beams) due to removing infill frames. Since this type of force has not been analyzed and designed, the frame is extremely damaged and stability is endangered. The following can be summarized as follows: • The presence of infill frames in building frames increases the initial stiffness and strength and the amount of energy dissipation and reduces the final displacement. • The presence of an opening in the infill frame does not always increase the ductility of the opening composite frames as compared to the nonopening ones; in fact, the ductility of the opening composite frames depends on the type of failure in the infill frames. • The middle opening in the infill frame wall reduces the stiffness and load-bearing capacity of composite frames. • The placement of openings at the corners of the wall has the lowest initial stiffness and ultimate strength due to its position on the compressor diameter compared to other modes. For this reason, it is recommended that openings be placed in the middle of the wall. • Composite frames that have openings with weak buttress and strong frontal beam show high energy-dissipation capability by creating obese hysteresis rings and distributing several cracks in frontal beam. Energy dissipation occurs as a result of friction attenuation phenomenon on cracks’ surfaces. Nonreinforced masonry infill frames, which have crisp or semicrisp behavior, do not perform well in severe earthquakes and suffer structural and nonstructural damage as partial cracks to crushing and destruction. Stiffness, strength, and energy absorption capacity deteriorate as a result of the fracture of the walls of the building material. In such cases, due to wall crushing and forces perpendicular to the infill frame, fragments of the wall may be thrown out of the frame and puts the life of residents at risk both inside and outside of the building.

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261

3.1.6 Common methods of seismic rehabilitation of masonry building Conventional seismic rehabilitation methods in masonry buildings are defined depending on the type of diaphragm of that building. In Chapter 2, Seismic Rehabilitation and Practical Methods in Seismic Rehabilitation of Existing Buildings, there were also references to the technique of intervention in determining the rehabilitation method as well as to the general structure of the building. In this section, I am trying to introduce you to the mental model of a seismic rehabilitation system for a masonry building. As we learned in Chapter 2, Seismic Rehabilitation and Practical Methods in Seismic Rehabilitation of Existing Buildings, seismic rehabilitation practices can involve general changes to the structure and partial to the elements. For example, when you install a brace in a building, it is true that the brace reinforces vulnerable elements, but it can have a relatively general effect on the existing building. However, when you seismically rehabilitate only the walls that are vulnerable, these walls are reinforced on their own and do not have a significant impact on building seismic load-bearing. In some cases, you use new systems, such as isolator, for seismic rehabilitation of existing buildings. You will find that if this building is in good consistency, it can have these systems installed in the right places, with overall effects on the stiffness and strength of the structure and ultimately its capacity. Based on the explanations given, we can conclude that for seismic rehabilitation of building materials, the most important parameter is the type of diaphragm system in determining seismic rehabilitation method. Also, if you want to use comprehensive systems such as base isolations that impact the entire structure in terms of seismic rehabilitation, complete and proper integration is essential for the building structure. So this parameter is in the second priority. As an engineer, if we want to distinguish the building in terms of the seismic rehabilitation method, we can see it as: floors level, foundation level, ceiling level, project site, and project general building [1,5,6].

3.1.6.1 General seismic rehabilitation of existing building In option one, we can examine a building in general for seismic rehabilitation. For example, if a building is vulnerable in terms of relative wall percentages, we can eliminate this problem by installing new secondary

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walls. The option offered under these conditions is to create cohesion and build secondary walls of masonry materials in the building. For option two, there is a building with a rigid or flexible ceiling diaphragm and a good consistency. All elements act in an integrated manner during an earthquake, but almost all elements are weak. Due to some arrangements it is not possible to use conventional seismic rehabilitation methods. However, we can accomplish a comprehensive seismic rehabilitation in the building by using base isolation in the common level of foundations and floors. In older buildings where new methods are not possible due to the intervention in the usage, for example, they can be seismically rehabilitated by inserting micro ties in the central core of the wall. Fig. 3.1.52 shows the building that has been seismically rehabilitated this way. Usually, the most common seismic rehabilitation methods in masonry building according the diaphragm types are classified as follows: If the ceiling diaphragm type is rigid, we can use the following methods for seismic rehabilitation. 1. Shotcrete walls and embedding vertical and horizontal ties (if not available). 2. Executing shear wall. 3. Executing braces. 4. Using FRP fibers. If the ceiling diaphragm type is flexible, we can use the following methods for seismic rehabilitation. 1. Shotcrete walls and embedding vertical and horizontal ties (if not available). 2. Executing shear wall and making the ceiling rigid. 3. Executing brace and making the ceiling rigid. 4. Using FRP fibers.

Figure 3.1.52 Example of seismic rehabilitation of traditional masonry building.

Types of existing buildings: detailed introduction and seismic rehabilitation

263

3.1.6.2 Seismic rehabilitation in components in the story level Walls as the most important member of such buildings can be rehabilitated in the following ways to heal damage such as weak walls, openings, dimensions, and consistency. 3.1.6.2.1 Correction of cracked spots 1. This method is used to create a uniform function in the masonry wall. In Fig. 3.1.53 you can see a demonstration of this type of seismic rehabilitation. 3.1.6.2.2 How to retrofitting with vertical and horizontal secondary ties Adjusting the length and height of the walls and the dimensions of the openings in the wall are done according to codecs. The vertical length of the wall can be reduced by applying vertical ties and standardizing the height of the horizontal ties. Ties can be implemented both in concrete and in steel in the form of secondary ties in the structure. Problems in walls that act as cantilever are solved this way (Fig. 3.1.54). 3.1.6.2.3 Procured of wall shotcrete In this type of seismic rehabilitation, we can increase the seismic capacity of the wall by creating a reinforced concrete layer with a thickness of approximately 10 cm one-sidedly or two-sidedly with steel reinforcement grillage of rebar and then pouring concrete over web surface. Due to the seismic rehabilitation method, the problems of length, height and cantilever of the wall and the dimensions of the openings in the wall are also eliminated (Fig. 3.1.55).

Figure 3.1.53 Correction of cracked spots.

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Seismic Rehabilitation Methods for Existing Buildings

Figure 3.1.54 How to retrofitting with vertical and horizontal secondary ties.

Figure 3.1.55 Procured of wall shotcrete.

3.1.6.2.4 Using FRP fibers These fibers can be used as secondary elements in the seismic rehabilitation of structural and nonstructural walls as well as consistency ties with their high strength capacities (Fig. 3.1.56). 3.1.6.2.5 Installing concrete shear wall In masonry buildings whose roof type is rigid diaphragm, it is possible to calculate numerically the need for the floor to depreciate the earthquake force by incorporating a new concrete shear wall (Fig. 3.1.57). After extracting the required length of shear wall in any direction, some existing walls can be demolished and replaced with new shear walls. These walls should be appropriately attached to the structural foundation and be fully reinforced in the construction site of the shear wall foundation.

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265

Figure 3.1.56 Using FRP fibers.

Figure 3.1.57 Installing concrete shear wall.

3.1.6.2.6 Installing steel brace with new frame In masonry buildings whose roof type is rigid diaphragm, it is possible to calculate numerically the need for the floor to depreciate the earthquake force by incorporating a new steel brace. After extracting the required length of braces in any direction, some existing walls can be demolished and replaced with new braces. These braces should be appropriately attached to the structural foundation and be fully reinforced in the construction site of the braces in foundation (Fig. 3.1.58).

3.1.6.3 Seismic rehabilitation of components in ceiling level Solution 1: Flexible diaphragms, as mentioned in Chapter 1, Understanding the Basic Concepts in Seismic Rehabilitation, occur on the floor arc, block joist, and light ceilings. The beams in these ceilings are generally not consistent, meaning they can have their own

266

Seismic Rehabilitation Methods for Existing Buildings

displacements when earthquake forces are applied. In this regard, one option is to create consistency for the beams in such roofs. The consistency method for these ceilings is such that the beam wings are joined together by some elements (Fig. 3.1.59). Solution 2: Another solution is to create rigidity in the existing diaphragm. This method is such that finishing material on the ceiling is removed to reveal secondary beams. After the secondary beams are exposed, the framing is done with appropriate fittings and spearheads and a secondary grillage of bars is formed. Concreting is done according to numerical calculations and as a result, the ceiling changes from a flexible to a rigid composite system (Fig. 3.1.60). Solution 3: Another solution is to reduce the weight of the ceiling if the diaphragm is rigid, but if the weight is more than the standard in relation to finishing surface, it should be reduced by appropriate such as thinning of the ceiling to reduce the earthquake force on the floors (Fig. 3.1.61).

Figure 3.1.58 Installing steel brace with new frame.

Figure 3.1.59 Seismic rehabilitation of components in ceiling level sample one.

Types of existing buildings: detailed introduction and seismic rehabilitation

267

3.1.6.4 Seismic rehabilitation in foundation level In masonry buildings, seismic foundation rehabilitation is done in two basic forms, namely, dimension change in existing foundation and second reinforcement of the foundation, each of which is presented in the form of Fig. 3.1.62. The numerical calculations required will represent the new dimensions and the new requirements.

Figure 3.1.60 Seismic rehabilitation of components in ceiling level sample two.

Figure 3.1.61 Seismic rehabilitation of components in ceiling level sample three ceiling coherence.

Figure 3.1.62 Seismic rehabilitation in foundation level for masonry wall.

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Seismic Rehabilitation Methods for Existing Buildings

3.1.7 Two real case study examples 3.1.7.1 Example of two-story reinforced masonry building with rigid and semi-rigid diaphragm 3.1.7.1.1 Introducing practical example 01 (building with brick masonry material) The present project is a two-story building with load-bearing walls system structures and brick masonry material with 1390 m2 area. It was pre-built in 30 years ago and today it has an educational use. This building is classified in none-reinforced masonry buildings. This building is open from all four sides. This project is located in a city with moderate seismic hazard and the peak ground acceleration (PGA) is used 0.25g according to the ratings of Iran Seismic Standard No. 2800. A notable point to consider is that there are two rigid diaphragm and flexible systems. According to the latest severe earthquakes which have occurred so far, decision has been made to evaluate the following building for the performance level basic target of building rehabilitation based on FEMA356 seismic rehabilitation regulations, and if needed, to present a suitable seismic rehabilitation method (Fig. 3.1.63) [4].

3.1.7.1.2 Qualitative vulnerability evaluation In qualitative evaluation of masonry building material, superficial damages of material are examined, and also required qualitative evaluation date are collected. Eventually, primary quantitative evaluation is done based on qualitative gatherings.

Figure 3.1.63 View of the studied project.

Types of existing buildings: detailed introduction and seismic rehabilitation

269

3.1.7.1.2.1 Geometric properties of the building

The present building is 35.7 m long and 22 m wide according to field inspection and available maps. Other properties of the building are in Table 3.1.26. 3.1.7.1.2.2 The ratio of height to width and length dimensions of the building

The ratio of height to dimensions in this building is calculated in the following. Based on the fact that these ratios are below 3, this building is not considered a slim one. ! !     6:65 6:65 H H 5 0:30 and 5 0:186 : 5 5 D D 22 35:70 N2S E2W

3.1.7.1.2.3 Type of roof system and building structure

According to the information received from the residents, digging was determined prior to any operations. The ceiling structure of the studied building on the second floor is concrete-block joists with rigid diaphragm and on the first floor it is a flexible diaphragm arch. The structure of this building consists of load-bearing brick walls which are perpendicularly executed. The walls continue from the top floor to the foundation. Due to the fact that there were no architectural maps available, the architectural as-built map was prepared by the resident group and presented for use in other cases. Architectural drawings include floor plans and building facades (Fig. 3.1.64). The first- and second-floor architectural plans were laid out in precise dimensions of the inner and peripheral walls so that they could be used with high precision in the separation of the walls for quantitative evaluation. This plan is one of the most important plans in projects with building material. Structural plans are drawn for the existing building after performing the required digging (Fig. 3.1.65). Table 3.1.26 Parameters to control of infill in the linear behavior. Floor name Area (m2) Effective architectural Height of the ceiling height of the ceiling (m) from the foundation (m)

First Second

695 695

3.50 3.10

4.55 7.65

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Seismic Rehabilitation Methods for Existing Buildings

Figure 3.1.64 Facade plan of the existing building.

Figure 3.1.65 Architect plan for the existing building.

3.1.7.1.2.4 Qualitative investigation of minimum shear strength

To evaluate the shear strength of a building, there must be at least some area of wall conditions. The area of existing wall value in each floor in each stretch is the ratio of the horizontal section area of the parallel structural walls to the desired floor area. To determine the wall area, only structural walls with a minimum thickness of 20 cm that have horizontal coils at the level below the ceiling shall be used. The top and bottom walls of the openings are not included in the calculation of the wall area (Table 3.1.27). According to the calculations in the north and south (Y) directions, walls area at a rate of almost 1% is low, and the building is vulnerable to numerical calculations without shear strength. 3.1.7.1.2.5 Determining the knowledge factor

The degree of validity of the results obtained from the existing building is applied by the knowledge factor K in the capacity calculation relationships of each component of the structure. Therefore in the above project, the

271

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selected knowledge factor for the given building is considered due to the lack of structural maps after defining the digging and testing agendas at the conventional level K 5 1. 3.1.7.1.2.6 Examining executive weaknesses in primary and secondary components and connections

Up to this section of studies (prior to digging) regarding the year of construction and the objective observations, it cannot be decisively commented on design defects and executive imperfections. In the qualitative evaluation based on the visit, traces of dislocation, adhesion, cracking, slump or corrosion were observed. As shown in Fig. 3.1.66, there are major weaknesses in building maintenance, resulting in a slight decrease in the quality of the material used for the walls. There has also been no proper cohesion for nonstructural components and may result in casualties at the time of the earthquake. Table 3.1.27 Control the percentage of wall area in floors. The wall area percent on the second floor Y

X

The wall area percent on the first floor Y

X

45 cm

Wall 45 cm Wall 45 cm Wall 45 cm Wall thickness thickness thickness thickness 62.30 m Wall length 108 m Wall length 62.30 m Wall length 106 m Wall length 28.03 m2 Wall area 48.6 m2 Wall area 28.03 m2 Wall area 47.7 m2 Wall area 4.0% 6.9% 4.0% 6.8%

Figure 3.1.66 Examining executive weaknesses in primary and secondary components and connections.

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Seismic Rehabilitation Methods for Existing Buildings

3.1.7.1.2.7 Symmetry status of building plans (in terms of mass and hardness)

Any geometrical protrusions in the building plan are symmetrical. Also, due to the relatively symmetric layout of the walls in the floors and the uniform mass distribution in plan and height, the floors are approximately symmetric in terms of mass and hardness. 3.1.7.1.2.8 The status of the openings and their proximity to the floor diaphragm

In the building, with the exception of the staircase, which is less than 50% of the floor area, there is an 5:20 m 3 5:20 m opening on the roof of the first and second floors on the north side of the building project (on the staircase). 3.1.7.1.2.9 Building’s components cohesion

According to the observations, in the brick masonry building material, if the connection between the perpendicular walls is well made, the structural integrity will be compromised. This can be checked after digging. Of course, in brick masonry building material that has vertical and horizontal roofs, cohesion is stronger than those without roofs. 3.1.7.1.2.10 Gravity and lateral load structure

In this building, the gravity and lateral load structure rely on load-bearing brick walls. 3.1.7.1.2.10.1 Evaluating regularity in a plan in terms of quality 1. Due to the relative symmetric geometric shape and symmetrical distribution of the walls, the center of mass and center of hardness appear to be less than 20% of the dimensions of the building per extension. 2. According to observations, there is no discontinuity in the direction of lateral force transmission. 3. Due to the relative symmetry of the bearing members in the building, the floors appear to be less than 20% relative to each other in relative displacement. 3.1.7.1.2.10.2 Evaluation of regularity in elevation in terms of quality 1. Examining the mass distribution at the height of the building means that each floor has no more than 50% mass difference from its lower floor. In the building and in the first and second floors, due to the low

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weight change of the ceilings in each floor, a slight change in walls and similar height of the floors will be met. 2. Lateral stiffness in any floor shall not be less than 70% of the floor stiffness of the floor itself or less than 80% of the average stiffness of the three floors on its own. According to the observations made, the lateral load-bearing system of the building relies on brick walls which will be met due to the similar height of the floors of this section. 3. Lateral resistance of any floor is not less than 80% of the floor resistance of the floor itself. 3.1.7.1.2.11 Evaluation of changes in the existing building plan

According to the study, no changes to the structural plan appear to have been implemented, but it is not possible to determine any possible changes to the structural plan due to the absence of an initial building architecture map. 3.1.7.1.2.12 General specifications of the site

Evaluation of fault potential requires careful application of the necessary procedures by the relevant experts; however, according to the studies and cognition that existed within the fault zone in and around the city, the project has not passed a specific fault, so the risk of faulting is very low unless a new fault is detected in the area or caused by a fault earthquake. As mentioned earlier, given that the city is within moderate seismic range, the basic velocity of the project is considered to be 0.25g. 3.1.7.1.3 Rapid qualification of vulnerability Qualitative evaluation based on numerical parameters according to the structural characteristics provides a quantification of the building vulnerability within a specific range. According to the rapid qualitative assessment of the vulnerability in this building, the qualitative value of 30.65% was calculated for the building. The building appears to be in the moderate range of vulnerability. But it is advisable to take a deep look at the vulnerability of the complete quantitative assessment structure after performing the required tests and digging (Table 3.1.28). 3.1.7.1.4 Digging and experiments To gather information at the standard level to determine the different specifications of the structural members and the executive details and to determine the specifications of building material, concrete, rebar, and

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Table 3.1.28 Rapid Vulnerability Assessment Quantity.

LR 5 0.45 3 [L3 1 L4 1 L5 1 L6 1 L7] 3 L1 3 L2 3 L8 3 L10 (7.5 A 2 1) # 100 30.65% # 100 Row Item name

1

2

3 4

5

6

7 8

9

10

Parameters

Coefficient Project

0 # Ø # 15 15 # Ø # 30 30 # Ø Soil type Type 1 Type 2 Type 3 Type 4 Foundation Suitable Unsuitable Masonry Wall Structural wall with vertical building and horizontal tie Structural wall with horizontal tie Structural wall with vertical tie Other lateral Moment frame 1 brace or Steel or frame system shear wall concrete building Moment frame Simple frame 1 brace or shear wall Simple frame Roof RC slab and steel deck system Block joist Arch roof Wood beam Protrusion In accordance with standard standards Out of standard Building plan Symmetrical Asymmetrical Windows and opening area In accordance with standard standards Out of standard Number of floor One floor Two floors Three floors or more Construction quality Good Medium Bad Land slope

Vulnerability

Low Middle

High

1 1.1 1.2 1 1.05 1.1 1.15 5 20 15

ü

ü ü ü

25 35 15 25 30 35 5 15 20 25 0

ü

10 0 10 1

ü ü

1.2 1 1.1 1.2 1 1.2 1.3

ü

ü

ü

LR

Maybe collapse

LR , 25% 25% # LR # 50%

50% # LR # 75%

LR $ 75%

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275

other consumables due to the absence of valid technical documentation, the minimum number of tests required is as follows. 3.1.7.1.4.1 Foundation digging

Foundation digging is performed on the points shown on the architectural as-built maps with at least five samples to determine the depth, dimensions, and type of foundation and to determine the arrangement of the reinforcement. Taking samples of foundation bars and rebar, tensile testing is performed to determine yield stress and ultimate stress of foundation and core reinforcement bars to determine compressive strength of concrete. 3.1.7.1.4.2 Digging vertical and horizontal ties and their connections

Digging vertical and horizontal ties at points shown on architectural asbuilt maps with at least nine samples to determine the dimensions of the tie, its location on the wall, its connection to the wall, and finally to determine the number and arrangement of longitudinal and truss reinforcement. Also evaluate rebar tension tests to determine the yield stress and ultimate stress, and coring of the coated concrete is performed to determine the compressive strength of the concrete. 3.1.7.1.4.3 Digging of ceilings

In visual observations, given that the second-floor ceiling was identified as a block joist, to determine the specifications of using joists including longitudinal bars and crossbars and dimensions of the concrete shoe and the location of the hidden connections and its attachment to the wall and detecting details of the block joist of the ceiling, beside digging for each floor, at least eight samples are required to perform the required steps. Also on the first floor ceiling, which is a type of arched arch with side metal joists, specifications of the whole floor beams and corrugated beams in the corridors, the presence of ceiling cross straps and the type and diameter of the restraining rod, specified and performed on the tensile test consumer profiles take action. The number of catheters for this story is also considered to be at least 8. 3.1.7.1.4.4 Masonry material sections

In this project, all the surrounding walls as well as those adjacent to the stairway are load-bearing walls with 45 cm thickness made with bricks. According to the standards, a minimum of one mortar shear test has been

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considered for each 30 m2 from walls. In the present project, due to the fact that all the brick wall areas are 45 cm, it was calculated to be 915 m2 after deducting the openings. Therefore the required number of mortar shear tests is estimated to be 8. Also, according to the current building condition, it is anticipated to reinforce the building using resistant brick walls to increase the lateral strength of the building. Therefore the number of mortar shear tests is limited to 8 to prevent possible damages to load-bearing walls. Mortar shear test is done to measure mortar resistance as to determine shear capacity of walls and also to remove architectural layer to check how walls and other masonry units are located and constructed, to determine the thickness of horizontal and vertical bounds and existence of masonry units to connect inner and outer rows. 3.1.7.1.4.5 Required tests to determine site specifications

To attain geophysical information, digging a minimum of one borehole is suggested, which contains a depth of at least 10 m or loading strain depth. This test is done to investigate geology of the region, type, thickness, and relative density of underground layers, characteristics of physical and mechanical layers, presenting strength limit and technical recommendations. Keep in mind that spotted digging plan and tests should be precisely prepared and accommodated to concerned groups and specialists. Examples of a plan and a table are provided for the readers to introduce the digging spots and tests. As you can see, the information is derived from Chapter 2, Seismic Rehabilitation and Practical Methods in Seismic Rehabilitation of Existing Buildings, as it follows (Table 3.1.29; Fig. 3.1.67). Table 3.1.29 Naming the location of tests on the plan. Row Components Material STORY

1 2 3 4 5 6 7 8 9 10

Foundation Vertical tie Horizontal tie Roof Beam Wall Tie connection Windows section Lintel beam Strain beam

Concrete Concrete Concrete Roof Any material Brick Concrete Steel Steel Steel

Base ST1 & ST1 & ST1 & ST1 & ST1 & ST1 & ST1 & ST1 & ST1

POSITION

2 2 2 2 2 2 2 2

FS-1 to 4 VS-1 to 4 HS-1 to 4 K1 to 2 BS-1 to 8 MS-1 to 8 HVS-1 to 2 W-1 WN-1 SS-1

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3.1.7.1.4.6 Evaluating the condition of members and components after digging

Determining the building configuration derived from digging and tests done on the building The photos taken while digging steel profile and consumed bars show that isolation has not been done properly in some sections and that oxidation and corrosion are vivid. The presented digging in construction of brick walls also shows that the thickness of some bounds of brickwork and less than 10 mm and some other over 12 mm and often exceed 50 mm in some cases. The thickness of horizontal bounds of brickwork are beyond limits. In addition, some vertical bounds of brickwork are not filled with mortar. The length of resting lintel is 30 cm, and its profile is double IPE140. There is not a vertical tie around the opening (Fig. 3.1.68). Connection between steel profiles on the first arch floor is IPE180, and on the second floor, the thickness of joists is about 40 cm, which lay 1.05 m from each other on the vertical tie (Fig. 3.1.69).

Figure 3.1.67 Placement plan for experiments.

Figure 3.1.68 Roof digging sample.

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Seismic Rehabilitation Methods for Existing Buildings

In this building, the total dimension of vertical ties is 30
37 cm, which include four longitudinal ribbed bars of 12 mm in diameter located every 20 cm from each other. The stirrups are 6 mm in diameter and laid every 25 cm all along the tie, which is not allowed to exceed 20 cm. The dimension of horizontal ties is equal to the load-bearing walls in width and is 30 cm high. The ties include four longitudinal ribbed bars in 12 mm diameter and 18 cm in length from each other, while this has to be at least six longitudinal bars. The stirrups are 8 mm in diameter and about 25 cm in length from each other all along the ties with no reduction in length near junctions. 3.1.7.1.4.7 Digging foundation

In this building, the foundation is located on the lean concrete of 10 cm thick. It is a stripe foundation with 40 cm depth and 70 cm width along load-bearing walls of 45 cm. The foundation includes ribbed bars of 12 mm in diameter and stirrups of 8 mm which are located 25 cm from each other (Fig. 3.1.70).

Figure 3.1.69 Floor beam planning of existing building.

Figure 3.1.70 Existing foundation plan.

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279

Figure 3.1.71 Borehole drilling to identify site soil.

3.1.7.1.4.8 Underground water and its fluidity background

The results of boring of soil show that the type of soil acquired includes several layers. Where the first layer at 15 m deep in the ground contains clay and silt with high resistance in dark brown color. The soil has become cemented from the 7-m layer on. According to the water leap wave speed 375ðm=sÞ , Vs , 750ðm=sÞ, the soil at this region is dense to moderate including gravel and dense sand to moderate with crusty clay with over 30 m in diameter (Fig. 3.1.71). 3.1.7.1.4.9 Test results to determine maximum and minimum of strength of material

The pressure resistance and elasticity coefficient of concrete To determine the pressure resistance of the concrete used in foundations and ties, two core with almost 9.3 cm in diameter from the foundation, one core from the horizontal tie with almost 7.4 cm in diameter, and three cores from the vertical tie with 7.5 cm in diameter are taken (Table 3.1.30). 3.1.7.1.4.9.1 Mortar Shear capacity test Mortar shear test was done at eight points and the results are presented as Table 3.1.31. 3.1.7.1.4.9.2 Schmidt Hammer test Concrete resistance estimation was done using Schmidt Hammer based on ASTM C085-85 standards in which the test results are provided in Table 3.1.32. 3.1.7.1.4.9.3 Steel members The yielding stress and ultimate resistance of plain and ribbed bars The bars used in the taken sample are ribbed. After doing the tension tests on the samples, the results are used in the next stages to determine the maximum and minimum resistance of the material (Table 3.1.33).

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Table 3.1.30 Existing concrete strength tests. Member

Position

Foundation Foundation Tie Tie Tie Roof

FS-1 FS-2 VS-2 VS-2 VS-3 K1

Section area Height Diameter (cm2)

w (g) MAX load (kg)

Crushing Strength (kg/cm2)

After coefficient correct

19.9 18.8 7.6 9.6 9.5 12.5

2987 2838 682 821 844 1115

483 456 70 0 77 50

474 447 59 0 69 47

Dimensions(cm)

9.3 9.3 7.4 7.4 7.5 7.5

67.93 67.93 43.01 43.01 44.18 44.18

32,800 31,000 3000 0 3400 2200

Table 3.1.31 Mortar Shear capacity test. Point Position Shear section ðcm2 Þ

Test load ðkgÞ

Vtest ðkg=cm2 Þ

1 2 3 4 5 6 7 8

2225 1700 1550 1700 4150 2500 1550 2875

5.066 2.35 3.02 2.4 Failure 5.82667 3.61 7.97033

MS-1 MS-2 MS-3 MS-4 MS-5 MS-6 MS-7 MS-8

360 380 342 380 380 380 380 342

Table 3.1.32 Schmidt Hammer test results. Point Position Loading angle Hammer no. (α) Stress (degree) degree (kg/cm2)

Possible error value (kg/cm2)

T13 T8

50 55

H-Tie H-Tie

0 90 1

27 40

Table 3.1.33 Bar tension test results. Member Floor Angle Diameter (mm)

Tie Tie

Story 01 0 27 Story 01 90 1 40

155 340

Yielding stress (kg/cm2)

Ultimate stress (kg/cm2)

Based on standard rating

3155 3340

5848 6358

AIII AIII

3.1.7.1.4.9.4 Mechanical test results The test results of the samples from the project are presented in Table 3.1.34. 3.1.7.1.4.9.5 Mechanical specifications of layers of soil From a seismic aspect of soil classification, shear-wave velocity in tests is estimated to

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Table 3.1.34 Mechanical test results on steel profiles. Member type

Floor

Height (mm)

Ceiling

Ground 398

Width (mm)

Thickness (mm)

Yield stress (mm)

Ultimate stress (kg/cm2)

Relative deformation (%)

Based on standards

11.2

8

3212

4329

29.3

ST-37

Table 3.1.35 Mechanical specifications of layers of soil. Layer NSPT C Φ

L1

. 50

. 300

10

ES

v

30

0.35

be almost 505 m/s. Other specifications of ground soil are derived from the test as in Table 3.1.35. 3.1.7.1.4.9.6 Compression strength of bricks in walls Due to the fact that brick materials in this project are in the range of average to good, pressure strength of 50 kg/cm2 is used. Elasticity module can be calculated using stress
strain curve slope between 5% and 33% for the pressure strength. Usually, the amount of elasticity module is 550 times more than expected pressure strength which is calculated Eme 5 2700 kg=cm2 for this project. The expected shear module, Gme , in considered to be 40% of the elasticity module of masonry material in pressure which is Gme 5 11; 000 kg=cm2 for this building. 3.1.7.1.4.9.7 Determining lower-bound strength It is equal to average amount of pressure resulted from the test minus one in deviation criteria. Based on the presented results, the lower-bound strength of vertical and horizontal concrete ties is 59 and 100 kg/cm2, respectively. The minimum compression strength for the horizontal concrete ties is 47 kg/cm2. About the concrete of the foundation, it is 447 kg/cm2. 3.1.7.1.4.9.8 Expected strength for materials The expected resistance of material used for average amounts is defined resulting from the test. According to the presented test results, the expected resistance of vertical and horizontal ties is 64 and 155 kg/cm2, respectively. The concrete used in the ceiling is 59 kg/cm2. The concrete used in the foundation, the expected resistance is 460 kg/cm2. Based on the results, the expected resistance related to longitudinal bars of A3 used in the foundation is 5848 kg/cm2 and the expected resistance related to longitudinal bars of A3 used in the joists is 6358 kg/cm2. According to the tests, the mortar shear capacity of Vme is 3.61 kg/cm2.

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3.1.7.1.5 Evaluating the demand for buildings to rehabilitate The aim of evaluating the present project is to reanalyze the structure based on FEMA 356 regulation and Iran magazine No. 376 in which the project needs to be presented for seismic rehabilitation. 3.1.7.1.5.1 Modeling for analysis

For the analysis of structures with soft and rigid diaphragms, a 2D model can be used in some cases. Due to the fact that 2D models can be used for the ceilings of this building, a 3D model has been used by the computer modeling program to ensure that the mechanism of the model and the real structure have similar behaviors. 3.1.7.1.5.1.1 Defining dead load and live load In the quantitative evaluation of the building vulnerability, determining gravity loads of the building for calculation and estimating features like average gravity stress, rudimentary shear, and collapsing is required. Therefore loading of dead and live should be done precisely. In this project, dead loads and live loads are in Table 3.1.36 (Fig. 3.1.72). 3.1.7.1.5.1.2 Determining primary and secondary members in the models according the diaphragm rigidity For modeling, all the existing walls with over 20 cm thickness are considered as main (primary) members. Main walls in this project has been divided to 45 number, which include 30 walls to be in X-direction and 15 walls in Y-direction (Tables 3.1.37 and 3.1.38). 3.1.7.1.5.2 Controlling foundation of the building

Due the fact that the values which are derived from the mentioned tables are less than the load-bearing capacity of the soil, the foundation of the building is not vulnerable and does not need to be retrofitted (Table 3.1.39). Table 3.1.36 Gravity loads alive and dead in the existing building. Dead load Live load Row

Name

Value

1 2 3 4

First floor ðkg=m Þ Second floor ðkg=m2 Þ External walls ðkg=mÞ Internal walls ðkg=mÞ 2

600 680 900 860

Row

Name

Value

1 2 3

Building use ðkg=m Þ Stairways ðkg=m2 Þ Roof (snow load) ðkg=m2 Þ 2

350 500 150

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Types of existing buildings: detailed introduction and seismic rehabilitation

Figure 3.1.72 Borehole drilling to identify site soil. Table 3.1.37 Geometrical properties of walls in floors for quantitative evaluation in X-direction. Wall Loaded Length Wall Loaded Length Wall Loaded Length number area (m) number area (m) number area (m) (m2) (m2) (m2)

1 2 3 4 5 6 7 8 9 10

2.99 9.36 9.43 19.06 44.99 9.88 3.25 3.13 9.81 9.81

1.05 1.60 1.60 6.49 8.84 1.80 1.15 1.05 1.60 1.60

11 12 13 14 15 16 17 18 19 20

10.08 3.41 60.03 36.00 24.97 5.65 31.19 26.35 14.95 40.40

1.70 1.15 12.64 5.88 3.36 3.45 5.79 2.64 1.75 5.89

21 22 23 24 25 26 27 28 29 30

30.20 33.40 10.16 10.16 10.16 3.61 3.34 10.16 10.16 11.90

5.58 1.15 1.80 1.80 1.80 1.25 1.15 1.80 1.80 1.80

σ , 3 qu-T 5 0:05H3=4 -0:05 3 ð6:65Þ0:75 5 0:21S -K 5 1 V 5 Sa W -0:6875 3 W ; Wstory01 5 998:5Ton ; and Wstory02 5 950Ton ; VBase Shear 5 1340Ton ; F2 5 824Ton ; F1 5 515Ton

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Table 3.1.38 Geometrical properties of walls in floors for quantitative evaluation in Y-direction. Wall Loaded area Length Wall Loaded area Length number (m2) (m) number (m2) (m)

31 32 33 34 35 36 37 38

2.4 0.9 0.9 2.34 2.45 17.28 25.84 17.48

5.35 1.15 1.15 5.2 5.45 5.35 5.65 5.35

39 40 41 42 43 44 45

0.54 9.46 2.45 2.41 0.9 0.9 2.34

1.2 5.2 5.45 5.35 1.15 1.15 5.2

Table 3.1.39 Evaluation of foundation. Weight A

σ

qu

Control

1950

1.07

0.97

Ok

201.32

3.1.7.1.5.3 Detecting vulnerable walls

Considering the modeling made for the current project on the first floor, as it was discussed before, the ceiling diaphragm is a flexible one. Thus according to the presented information in evaluation method of the masonry building material section, in this case, the contribution of each member to the earthquake force is calculated by calculating the effective mass ratio of that member to the total mass of its floor. By analyzing and evaluating the structure of the second floor, based on the fact that the ceiling diaphragm of the second floor is rigid, in this case, the contribution of each member to the earthquake force is calculated by calculating the effective stiffness ratio of that member to the total stiffness of its floor (Fig. 3.1.73). The shear capacity of the first floor in north and south directions is 964 tons, while the shear force on the same floor equals 1340 tons, which means that the force increases about 40% compared to the capacity. A more precise analysis revealed that the walls on the first floor in north and south directions are vulnerable. On the second floor, the analysis showed that the walls in north and south directions have less stiffness. Finally, four walls were detected to be vulnerable and should be seismically rehabilitated. It is noteworthy that the shear capacity on the second floor is 964 tons, which is more than the applied shear force (824 tons). This shows that the shear capacity of the floor is approximately 17% higher than the shear force will applied to it during earthquake (Fig. 3.1.74).

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Types of existing buildings: detailed introduction and seismic rehabilitation

Figure 3.1.73 Calculate the contribution of earthquake force in members.

Figure 3.1.74 Masonry wall behavior. Table 3.1.40 Vulnerability study of a wall sample. Wall Story Direction Loaded area number name (m2)

36

First

Y

34.56

m=ðΣ mÞ Iðm4 Þ

0.089

Aðm2 Þ

5.487172 2.3005

Row Acceptance criteria

Strength m

failure mode Capacity ðTonÞ

Force ðTonÞ

DCR

1 2 3 4 5

QCE

Sliding 72.45 Rocking 73.09 Diametric 128.9 Heel crash 63 Compressive 391

216.2 216.2 148.2 148.2 26.75

0.99 1.76 1.15 2.35 0.07

Deformation controlled Force controlled

QCL

3 1.68 1 1 1

To better understand the example, the results are presented as a case study in the first floor for the 36th wall. As you can see, wall is vulnerable (Table 3.1.40). 3.1.7.1.6 Presenting seismic rehabilitation solution for the building Providing lateral stiffness required for the whole structure, providing lateral stiffness in this building has only been fulfilled using masonry material walls. Due to the fact that the vulnerability of this building more likely

286

Seismic Rehabilitation Methods for Existing Buildings

results from lack of shear capacity of seismic elements, a solution is required to be presented to rehabilitate them, where strengthening the walls generally increases the stiffness of the walls, and therefore, results in an increase in stiffness of the floor. 3.1.7.1.6.1 Providing lateral stiffness required for the whole structure

As it was mentioned in the analysis section of quantitative vulnerability of the building, the shear resistance required for buildings with masonry material is attained by load-bearing walls within a structure in X- and Ydirections. Therefore in this section to eliminate the shear resistance weakness against rudimentary shear based on FEMA 356, several methods are suggested for reinforcing the current structure. These methods are presented as the following: • Increasing the resistance of the building using reinforcing walls with shotcrete In this method, the shear resistance of the structural walls available increases by a new layer of reinforced concrete used for the walls (Fig. 3.1.75). 0

Knew 5 Kwall 1 KShotcrete ; K 5 @

1

1 h3eff 12Em Ig

1 AhveffGm

0

A

1@ Wall

1

1 h3eff 12Em Ig

1 AhveffGm

A Shotcrete

•

Increasing the resistance of the building by none-rigid reinforced ceiling walls with shotcrete In this method, by removing elaborate work of arch wall of the ceiling and implementing a layer of rebar net and then applying concrete for 10 cm, we can increase the rigidity of the ceiling, and as a result, distribution of seismic force shifts from distribution based on stiffness to distribution based on mass. In this case, the structure goes under quantitative

Figure 3.1.75 Wall seismic rehabilitation method with shotcrete wall (concept one).

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287

Figure 3.1.76 Ceiling seismic rehabilitation method.

Figure 3.1.77 Using FRP for seismic rehabilitation (concept three).

evaluation again until its vulnerability condition is checked after being rehabilitated with rigidity method (Fig. 3.1.76). • Rehabilitating the building using FRP In this method, with a proper concrete substructure, FRP sheets are installed on vulnerable walls of the building and lead to an increase in shear resistance of the floor. Therefore using FRP composites can also reduce the vulnerability of the building against shear of the floor (Fig. 3.1.77). 3.1.7.1.6.2 Making consistency in arch ceilings

One of the solutions of reinforcing arch ceilings is to use transversal beams within ceiling beams. Therefore the ceiling beams should be located every 2 m and not more from transversal where they connect the arch beams. For this reason, some rows of arch bricks are removed from transversal beam connection, and the main beams are cleaned at the connection (Fig. 3.1.78). Next, if the transversal beams are smaller than the main beams, a simple in-site welding can be used with two proper bevels to connect the

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Seismic Rehabilitation Methods for Existing Buildings

Figure 3.1.78 Making consistency in arch ceilings.

web of the two beams. If the section of the transversal and longitudinal beams is equal, the two beams can be conjoined using a bevel as the following. 3.1.7.1.6.3 Evaluating execution time

The expected time of executing seismic rehabilitation plans in the current buildings is 38 days for the shotcrete of walls and 66 days for the rigidity of ceiling and shotcrete of walls and 23 days to perform FRP. Therefore it seems that when analyzing the executive time, rehabilitating by FRP method is a better choice. 3.1.7.1.6.4 Evaluating execution cost

The execution cost shows that seismic rehabilitation cost in FRP method has the highest amount, and other choices like shotcrete of walls and rigidity of ceiling are second and third priorities, respectively. It can be inferred that according to the cost of seismic rehabilitation, shotcrete of walls is the best choice. 3.1.7.1.6.5 Evaluating advantages and disadvantages of seismic rehabilitation plans

In rehabilitating buildings with rigidity of ceiling and reinforcing walls with shotcrete, superficial weaknesses of walls like controlling the size of openings and length of walls as well as increasing shear resistance of floor and ceiling consistency and predictable force distribution have been solved, but in methods where executing shotcrete of walls and using FRP composites, although the resistance of the floor increases, some actions should be done to solve superficial weaknesses.

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289

3.1.7.1.6.6 Evaluating required facilities and equipment and skills of local labor to execute suggested options for rehabilitation

As it can be seen, the executive method of leveling walls with shotcrete and consistency of the ceiling is relatively advantageous compared to other options and that is because this method requires special machines which have become customary by increasing resisting projects compared to other equipment. 3.1.7.1.6.7 Inconveniency for users or temporary suspension of the building usage

Reinforcing walls in a building will be coincided with demolishing sections of the structure. Choosing or executing a reinforcing plan should have the minimum inconvenience to the users and if possible, not have a temporary suspension of the building usage. Therefore, according to the area of the building and its rehabilitation essence, it will lead to suspension. In this case, time will be so effective. 3.1.7.1.6.8 Evaluating demolishing volume of suggested executive options for rehabilitation

Due to the fact that demolishing operations are part of rehabilitation operations, and that demolishing exists in all suggested methods, it is quite different in various methods. Demolishing operation in reinforcing wall method is equal to using FRP composites because in both methods the walls are rehabilitated which are vulnerable in terms of shear resistance. Therefore, in the rigidity of ceiling method and reinforcing walls, bottom floors should be removed as well as removing the elaborate work so that rigidity operations of the ceiling is executed. Also, it is important to mention that the operation of demolishing has been limited in executing method of shear wall to the foundation. In the other methods, however, demolishing volume operation is more than executing shear wall method. 3.1.7.1.7 Conclusion As it was previously mentioned in the evaluating quantitative section of vulnerability studies of a building, the lateral load-bearing system of the current building is a load-bearing wall with horizontal and vertical ties which was defined in the vulnerability analysis of the building where the walls had no major weakness in terms of shear resistance, and a number of current walls have enough efficiency compared to the incoming forces without considering walls in north and south directions on the first floor.

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In all cases of the building, consistency of the ceiling and the length of some walls are considered to be vulnerable. Overall, to solve the problem of the size of vulnerable openings, using ties with concrete and steel elements is suggested. It needs to be mentioned that solutions for the ceiling and stairway consistency and controlling steel sections and presenting a rehabilitation solution should be considered. Therefore three options of retrofitting vulnerable walls were evaluated by implementing shotcrete, stiffening the ceiling and reinforcing the walls, and also retrofitting vulnerable walls using FRP polymer filer in the building. Based on the analysis, the shotcrete of walls was a better option and more suitable than the other choices in terms of technical and economic matters. Thus this option (retrofitting walls using shotcrete) was considered to be the best rehabilitation option (Figs. 3.1.79 and 3.1.80).

3.1.7.2 Example of one-story unreinforced historical masonry building with nonrigid diaphragm The example presented here is for a one-story building with masonry walls and dome roofs made of adobe material with plaster of clay and straw. The site of the construction is in the historical city of Bam. Given that the city was hit by an earthquake in December 2003 and ultimately caused irreparable financial and life damage in the urban context, the maximum acceleration recorded in the Bam earthquake on the vertical component is 0.989g. The earthquake also caused damage to unique adobe historical buildings. In this example, while evaluating the building under study, interventional and noninterventional seismic rehabilitation techniques are presented for specific seismic rehabilitation. 3.1.7.2.1 Why should adobe buildings be rehabilitated? Reports and observations regarding earthquakes in Iran, which is considered as one of the seismic regions of the world, indicate that in earthquakes such as Bam earthquake on 5 January 2003 and Zarand earthquake on March 2004 as contemporary earthquakes and old earthquakes such as the Tabriz earthquake of 1780 have caused irreparable damage to urban and rural adobe buildings. These buildings, which are predominantly historic, are very important in terms of cultural heritage, and their preservation is essential for the next generation. For example, the Bam earthquake of 2003 has caused 90% of one of the most unique adobe buildings in the historical city of Bam dating back to 2500 years

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Figure 3.1.79 Detail of seismic rehabilitation story one.

old. It is worth noting that in many parts of the world, especially in desert regions, people still live in insecure adobe houses. Therefore, due to the historical longevity and age of these buildings for immediate occupancy in earthquake hazard level two, studies will be necessary. One of the most useful measures is the risk segmentation of these structures in 1994 by the American Institute of Earthquake Engineering

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Figure 3.1.80 Detail of seismic rehabilitation story two.

Research. The effects of destruction can also be divided into four main categories, local destruction effects, retaining collapse risk, structural destruction effects, and collapse risk for building’s structure (Fig. 3.1.81).

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Figure 3.1.81 Bam, which was nearly destroyed up to 90% after earthquake on 2003.

3.1.7.2.2 Difference between restoration and rehabilitation in adobe buildings In seismic rehabilitation of historical buildings two important principles must be distinguished: (1) the principle of restoration (localized seismic rehabilitation of existing rehabilitation); (2) the principle of rehabilitation to protect the building against possible earthquakes and to prevent possible damage. Unfortunately in today's engineering, according to a common ground between civil engineers and architects about such projects, there is a contrasting taste with engineering calculations. Therefore it can be said from the point of view of architects, the rehabilitation process is more of a local approach than a general project rehabilitation approach (Fig. 3.1.82). 3.1.7.2.3 The progressive damage mechanism in adobe buildings In these buildings due to the high mass resulting from the thick brick walls on the one hand and the lack of proper coherence between the elements forming the walls, on the other hand, they vibrate greatly during the earthquake configuration of the walls. In this case, the walls move in or out of the plate, causing deep cracks in them, resulting in disruption to their performance level. 3.1.7.2.4 Project introduction 3.1.7.2.4.1 Configure and recognize existing building specifications

It is a one-story building with a regular geometrical plan of the walls, with a height of 3 m on the sides and 4.50 m on the crest of the domes. The type of usage was originally residential, but due to historical age, it

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may be possible to change the usage to the cultural heritage building (Fig. 3.1.83). The walls are of adobe type, the thickness of the sidewalls is about 65 cm, the bricks are executed in 20 cm 3 20 cm 3 4:5 cm dimensions, and the middle walls of the common season are 80 cm. All the walls and ceilings are covered by lattice mortar in a good way (Fig. 3.1.84). The thickness of the existing ceilings is about 35 cm, which was determined to be 15 cm at the time of construction, which has been added to its thickness over time due to the thickness of the fine work. The

Figure 3.1.82 Local seismic rehabilitation of a historical building with wood.

Figure 3.1.83 Elevation view of building’s walls and roof.

Figure 3.1.84 Three-dimensional schema of wall placement.

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thickness of the existing ceilings is about 35 cm, which was determined to be 15 cm at the time of construction, which has been added to its thickness over time due to the thickness of the work. The porthole is a multipurpose vault that has a thickness of one raw brick. The walls and ceilings are covered with plaster and dirt. 3.1.7.2.4.2 Site specifications

As mentioned, the building is located in the Bam area with high seismic risk. The most likely acceleration in the future and in the useful life of any structure may be caused by an earthquake, based on Iranian seismic codes for the area is about 0.3g, but as noted earlier. However, regarding the site soil type, Iran's seismic bylaws are in the category of three conventions, namely the wave velocity for a level up to a depth of 30 m below the level under foundation is 175 # vS ðm=SÞ # 375. 3.1.7.2.4.3 Determine the weight of the building and its effective period

Taking into account the specific weight of the adobe wall per unit of cubic meter, which is 1610 kg=m3 , the dead weight of the building is 132 tones. The weight of the snow layer on the ground is estimated to be 50 kg=m2 with a 50-year return period with a probability of 2% per year. Due to the type of dome roof, this time is reduced to 8 kg=m2 according to the loading coefficients applied in the loading regulations, which are ignored in this project, and only seismic calculations based on dead weight of the building are performed (Fig. 3.1.85). 3.1.7.2.4.4 Determination of mechanical properties of materials used by experiments

Due to the fact that samples could not be sampled due to architectural changes, samples were taken around a building with exactly the same conditions and could be demolished and transferred to the laboratory for

Figure 3.1.85 Clay dome roof.

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Table 3.1.41 Determination of compressive strength. Row Sample number Deamination (cm) Force (kg)

1 2

10:5 3 10:3 0:95 3 10:4

B-1 B-2

2854 2568

Compressive strength

26.38 25.99

Table 3.1.42 Determination of primary shear strength of adobe materials. Row Cohesion adobe materials (C) Internal coefficient of friction of adobe materials

1

2.68 KN

1.27

speciation. Experiments were performed to determine the compressive strength of adobe bricks and to determine the shear strength of mortar. The number of samples for each experiment in this project is 3 (Tables 3.1.41 and 3.1.42). 3.1.7.2.4.5 Quantitative assessment of adobe load-bearing wall capacity

As can be seen, the type of ceiling aperture system is flexible depending on the type of connection. In this regard, as already mentioned, the contribution of each wall to the earthquake force is the proportion of the effective mass contribution of that wall to the floor mass. First step: In this regard, we first call the walls in each direction in the proper manner according to the following numbering so that the materials can be accurately referred to when evaluating and presenting the rehabilitation plan (Fig. 3.1.86). Second step: Determining the amount of potential earthquake force on a building According to FEMA 356 and Iran 376, the earthquake force is determined as follows and is distributed among the walls as described earlier. TX 5 Ty 5 0:15S When a building is influenced by earthquake hazard level 1: V ðFor BSE-1Þ-V 5 CS 3 W V 5 0:825 W-V D109; 000 kg When a building is influenced by earthquake hazard level 2: V ðFor BSE-2Þ-V 5 CS 3 W V 5 1:03 W-V D136; 000 kg

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Third step: The capacity of each wall is determined according to the components of mechanical properties and related criteria. These are the criteria set forth in Section 3.1 for unarmed building materials that meet the requirements of code no.(376) of Iran and FEMA 356. To determine the shear capacity of the materials used in the adobe, the values of the coefficient of consciousness and m are considered. It seems that the behavior of these walls is deformation controlled (Table 3.1.43). DCR 5

QUD mKQCE

As you can see, all the walls are vulnerable and can crack and break when the earthquake strikes. Fractures and cracks in these walls lead to a severe loss of capacity and collapse, so a comprehensive plan for seismic rehabilitation of these walls should be presented. Following is an example of the intended seismic rehabilitation plan.

Figure 3.1.86 Divided and numbering of walls. Table 3.1.43 DCR control. Walls in X-direction

Walls in Y-direction

(No)

Bearing capacity (kg)

QUD ðkgÞ

DCR

(No)

Bearing capacity (kg)

QUD ðkgÞ

DCR

1 2 3 4 5 6

12,437 12,437 16,582 16,582 12,437 12,437

17,000 17,000 34,000 34,000 17,000 17,000

1.36 1.36 2.05 2.05 1.36 1.36

7 8 9 10 11 12 13 14

8754 4765 22,179 13,425 8754 4765 22,179 13,425

11,000 11,000 28,000 17,000 11,000 11,000 28,000 17,000

1.25 2.3 1.26 1.26 1.25 2.3 1.26 1.26

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Figure 3.1.87 Seismic rehabilitation method, using micropile.

3.1.7.2.5 Providing a seismic rehabilitation plan For this building, we can use two systems, visible intervention and hidden intervention for seismic rehabilitation. Visible system means using meshing network or visible FRP which aims to increase load-bearing capacity of adobe walls. Regarding that most of adobe and old buildings are historically valuable and are considered cultural heritage, therefore this method is not usually recommended. The second method is hidden intervention system which uses micropiles inside wall plates. Further, hidden seismic intervention system with micropiles inside walls is explained. Advantages of hidden intervention system include maintaining internal and external facade of the building. In this method, first holes with given distances are made vertically on top of the walls and then steel pipes are placed inside these holes and the rest of the space is filled with glue or mortar. If these cores are connected to the upper belt, they can create an integrated system which can create significant consistency in the structure besides increasing the nominal capacity of walls. Regarding the thickness of the upper parts of the adobe walls, the depth of these holes must be lower than the level of window openings. It is recommended that two micropiles are placed in border element of openings. In this building, using horizontal micropiles is not recommended due to the height of the walls. However, facing with a building in which heights-to-thickness ratio is not reasonable, and in which applying earthquake force leads to out-ofplate cracks, using horizontal micropiles will be necessary (Fig. 3.1.87).

References [1] Islamic Republic of Iran Management and Planning Organization: (code.No.376), Instruction for Seismic Rehabilitation of Existing Unreinforced Masonry Buildings, Office of Deputy for Technical Affairs, Tehran, 2007. [2] Islamic republic of Iran Vice Presidency for Strategic Planning and Supervision: (code. No.360) first revision, Instruction for Seismic Rehabilitation of Existing Buildings, Office of Deputy for Strategic upervision, Tehran, 2014.

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[3] American Federal Emergency Management Agency (FEMA.356), Prestandard and Commentary for the Seismic Rehabilitation of Buildings, Reston, VA, November 2000. [4] Iran Road, Housing & Urban Development Research Center (Iranian Standard. 2800), Forth Edition of Building Design Codes against earthquake, Tehran, 2015. [5] Federal Emergency Management Agency (FEMA) (2000), Prestandard and Commentary for the Seismic Rehabilitation of Buildings. [6] Federal Emergency Management Agency (FEMA) (1997), NEHRP Commentary on the Guidelines for the Seismic Rehabilitation of Buildings (FEMA 274), Reston, VA.

Further Reading American Concrete Institute American Concrete Institute: (ACI 318/14), Building Code Requirements for Structural Concrete, Farmington Hills, 2014. American Society American Society of Civil Engineers (ASCE/SEI 7-10), Minimum Design Loads for Buildings and Other Structures, Reston, VA, 2010. ASCE, 2013 ASCE, Seismic Rehabilitation of Existing Buildings (ASCE/SEI 41-13), American Society of Civil Engineers,, Reston, VA, 2013.

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Masonry structure building seismic rehabilitation at a glance

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SUBCHAPTER 3.2

Concrete structure frame buildings Aims By reading this chapter, you are introduced to: • getting acquainted with all types of buildings build with concrete structures; • getting acquainted with the methodology of evaluation of different types of concrete structure buildings; • understanding the methodology of foundation evaluation; • learning about seismic rehabilitation methods; and • understanding the chapter topics in depth by studying two practical examples of the end of this chapter.

3.2.1 Types of concrete structure buildings The structure of the concrete buildings discussed in this book, regarding common structures, is divided into three types: concrete frame structures, structures with shear wall and rigid diaphragm, and concrete frame structures with shear wall [1
3].

3.2.1.1 Type one: concrete frame structures 3.2.1.1.1 Concrete moment frame In this type of concrete buildings, gravity and seismic load are transmitted to the columns by beams. Finally, the forces are transferred from the columns to the foundation. The connections in these types of structures are full rigid as a moment connection (Fig. 3.2.1). 3.2.1.1.2 Concrete simple frame or concrete frame Beams and column connections are pin and simple in the structure of such buildings. In this type of structures all elements are made and assembled at the project site. 3.2.1.1.3 Concrete frame with pin connection and precast sections Beams and column connections are pin and simple in the structure of such buildings. Generally, the structural skeleton of residential buildings

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Figure 3.2.1 Concrete moment frame.

Figure 3.2.2 Concrete frame with pin connection and precast sections.

and some of the less than four-story buildings are constructed in this way; this means that in this type of buildings the connections cannot bear any moments. It should be noted that in this type of structure some elements are precast and are connected by pin connections (Fig. 3.2.2).

3.2.1.2 Type two: frame less structures with shear wall and rigid diaphragm 3.2.1.2.1 Shear wall Shear wall is a structural member used to resist lateral forces, that is, parallel to the plane of the wall. For slender walls where the flexural deformation is more, shear wall resists the loads due to cantilever action. In other words, shear walls are vertical elements of the horizontal force resisting system. In this type, concrete structures are generally designed in such a way that the lateral seismic load and gravity load is bearing by consistent shear walls. These structures have no beams or columns, and the earthquake-resistant system relies solely on concrete shear walls (Fig. 3.2.3).

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Figure 3.2.3 System with consistent shear wall.

Figure 3.2.4 Concrete column system and rigid diaphragm.

3.2.1.2.2 Concrete structure column and rigid diaphragm structure (beam less structure) In this type of concrete structures, diaphragm of roof is implemented using modern construction technology with considerable rigidity. In some cases, the ceiling beams are removed and such structures based on columns and rigid diaphragms. Finally, during an earthquake, the lateral load is directly transferred from the diaphragm to the column (Fig. 3.2.4).

3.2.1.3 Type three: combined or dual concrete systems 3.2.1.3.1 Concrete simple frames with shear wall In this type of concrete structure, since the connection of the frame beams to the columns is semirigid, it is only able to bearing gravity loads .Other loads such as earthquakes and wind is bearing by shear walls and then driven to the foundation (Fig. 3.2.5).

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Figure 3.2.5 Semirigid concrete frame including shear wall.

Figure 3.2.6 Flexural frame system and shear wall.

3.2.1.3.2 Concrete moment frame including shear wall In buildings over 50 m, the deformation may be so high that it can cause cracks in walls and windows or even cause severe psychological reactions in building occupants. Therefore moment frame and shear wall are used together to provide lateral rigidity of the building. Considering the deformation of all the systems consisting of shear walls and moment frames that interact with each other, this deformation is obtained by the sum of the individual deformation modes of the wall and frame (Fig. 3.2.6).

3.2.2 Understanding potential structural damage Concrete structures as a large part of structures will be more favorable if designed and executed on the basis of precise calculations and ductility relationships. However, the quality of construction in some

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structures is poor for various reasons. Poor quality of concrete, inadequate reinforcement, bad concreting, inadequate materials, design errors, execution errors, increased structural load, impact of destructive environmental circumstances, and earthquake hazard in such area are among the factors that make concrete structures weak, needing seismic rehabilitation. Many existing reinforced concrete structures designed and implemented according to regulations before 1970 have poor reinforcement details that include problems such as low lateral displacement capacity, low energy dissipation capacity, deterioration in strength, and mechanism failure in unfavorable parts of the structure; all of which lead to the collapse and destruction of the structure. Details of vulnerability in ductility of reinforced concrete structures in the form of weak connection shear strength due to lack of transverse reinforcement in the connection core, low shear capacity of the column leading to the connection, low overlap length of column longitudinal reinforcement, non-compliance with beam length and compression Insufficient restraint of beam reinforcements in the connection area is considered. Weakness in the beam to column connection area, along with adverse factors, “weak column and strong beam” endangers the stability of the structure.The occurrence of the mechanism in the beam is preferable to the column, and the column mechanism is less critical than the connection area (Fig. 3.2.7). The occurrence of a mechanism and plastic hinge at the beam-tocolumn connection leads to increased twists in the beam and column, which undermines the bearing capacity of the column and affects the structural safety. To investigate the seismic rehabilitation of concrete structures, it is necessary to identify different types of damages in concrete

Figure 3.2.7 Corrosion in concrete and rebars.

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structures. Therefore different types of localized weaknesses in members of concrete structures are as follows: • Weakness according to the dimensions of the sections. • Creation of oblique cracks in the concrete core. • Exfoliated Concrete core in most oblique cracks resulted from earthquake load shaking. • Detached concrete cover. • Detached stirrup and protrusion in their places. • The shear failure modulus of short elements attached to sides and whose effective unbrace length is low. • Buckling phenomenon in longitudinal reinforcement. • Protrusion of bars from the primary position and into areas of high stress. • Cracks in reinforced concrete slabs on noncontinuous sides. • Diagonal cracks in the shear wall, especially concentrated around the openings. • Creating shear cracks at the nodes and at the beam junction. • Common problems with concrete slab—corrosion and porous of concrete surface.

3.2.2.1 System weakness in concrete buildings Due to the way the elements are positioned in concrete buildings, there can be major problems with the lack of stiffness and mass in the structure that can include: soft story phenomenon, structural inconsistency, and building collapse.

3.2.3 Rapid vulnerability assessment In concrete buildings, a rapid qualitative assessment of vulnerability can be done based on the material presented in Chapter 2, Seismic Rehabilitation and Practical Methods in Seismic Rehabilitation of Existing Buildings. A seismic rehabilitation engineer can classify the contents of the damages that are likely to occur and determine the vulnerability of the structure when evaluating a building by defining numerical parameters in a specific area. The rapid vulnerability assessment should be noted in accordance with the criteria presented in FEMA 310, which has

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the most qualitative approach, some of the rapid assessment parameters in concrete buildings to be examined include [1
4]: • Number of frames: The number of frames in each direction adjusted for functional life safety is 2 and for immediate occupancy is 3. • Internal walls: It should be made of insulated resistant frames. • Connection: All columns must continue into the foundation, and the brace length of the reinforcement must be able to provide the column's tensile strength. • Short column: The ratio of height to dimensions of the column must not be lower than 50% of the standard samples on that floor. • Weak beam strong column: The total moment capacity of the columns is 20% more than the moment capacity of beams per node. • Beam reinforcement: There must be at least two continuous longitudinal upper and lower reinforcement and at least 25% of the required reinforcement on the positive or negative columns along member. • Reinforcement splice of columns: The minimum columns' splice length is 35 times the diameter for life safety and 50 times for immediate occupancy use of stirrup with a distance less than 8 times the diameter of the longitudinal reinforcement. • Splice reinforcement of beams: Splice of reinforcements shall be at least L/4 from the support and away from the plastic hinge formation area. • Stirrups in beams: Maximum d/2 in the middle and 8db in the sides or d/4 in the plastic hinge. • Reinforcement at nodes: stirrups at intervals of at least 8db. • Pins and stirrups: The stirrups of the beams and pins in the columns must be restricted to the core at a minimum angle of 135 degrees. • Compatibility of displacement: Secondary components must have adequate shear capacity to provide flexural strength of the elements as well as provide details of ductility for instantaneous operation level. • Shear stress control: Shear stress in columns and concrete shear walls shall be less than 0.7 MPa using the rapid evaluation method. • Axial load stress control: the stress due to the gravity loads in the columns with inversion forces less than 0.1Fc or the stress due to the calculated inversion forces alone can be less than 0.3Fc. • Lack of shear failure: The shear capacity of the frame members must be able to convey the bending capacity at the two ends of the column. • Control of reinforcement ratio in concrete shear walls is 0.0015 vertical and 0.0025 horizontal and less than 45 cm.

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Interface beams on concrete shear walls: The beams in these beams have d/2 distance, the interface beams have adequate shear capacity to adjoin the adjacent wall. Interface beams in concrete shear walls: The stirrups in these beams have a d/2 distance, the interface beam must have the proper shear capacity for adjoining the wall. Overturning: The walls must have an appearance ratio less than equal to 1
4 the length.

3.2.4 Comprehensive assessment of vulnerabilities Since many concrete structures may have been reinforced over time, this chapter presents content that incorporates the regulations and criteria of acceptance for reinforced concrete components of existing buildings [1
3] (Fig. 3.2.8). Seismic rehabilitation of concrete structures is the evaluation and examination of seismic rehabilitation of all constituent elements of concrete structure, including concrete foundations, beams, columns, and connections in moment frames and shear walls.

3.2.4.1 Specification of materials The specification of materials needed for the seismic rehabilitation evaluation of existing concrete buildings is determination of compressive strength and elasticity coefficient for concrete and tension yield and ultimate strength for any reinforced concrete, whether ordinary or pretensioned and other steel parts used in the studied building for all components studied in the seismic rehabilitation process. These

Figure 3.2.8 Chart of divided story level for seismic rehabilitation of concrete building.

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specifications, as noted in the previous chapters, are derived from the test results [1
3]. 3.2.4.1.1 Lower-bound strength of concrete materials The lower-bound specifications are extracted according to one of the following methods: 1. Specifications of the lower-bound strength of materials derived from the calculations and available plans and tests that are performed at the time of execution and documents are accessible. 2. The mean of the results obtained from the documents at the time of execution minus one standard deviation. 3.2.4.1.2 Expected strength of concrete materials The expected specifications of the materials are also extracted from one of the followings: 1. The expected values of the materials are determined by the mean values obtained from the tests. 2. The expected properties of the materials are derived using the following relationship (Table 3.2.1). QCE 5 QCL 3 α

(3.2.1)

Although the above coefficients are presented in the FEMA 356, it should be noted that these coefficients are the maximum values. In this regard, it is recommended to consider rows 1 and 3 of between 1.25 and 1.5 for coefficient. This is due to the difference in the way materials are used and the quality of the material in different regions of the world.

3.2.4.2 Digging required in quantitative evaluation and modeling of building structures In concrete structures, in order to identify the exact characteristics of the components, we need to perform diggings in effective locations. In this Table 3.2.1 Coefficients for converting lower-bound specifications to expected material specifications [1]. Row Coefficient Material specifications Concrete components

1

1.50

Compressive strength of concrete

Steel (bars) components

2 3

1.15 1.50

Tensile tension and rebar yield strength Connector steel yield strength

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regard, the classification of components who need a digging is very important. In the Fig. 3.2.9, this category is presented for the concrete building structure components.

3.2.4.3 Number of tests required at least based on seismic rehabilitation objectives As this experiment has been thoroughly evaluated and tested in the Section 2.2.2 “experiments and digging,” Fig. 3.2.10 is presented to

Figure 3.2.9 Required digging in concrete building.

Figure 3.2.10 Requirements experiments and test for seismic rehabilitation of concrete buildings.

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remind readers of the comprehensive and common tests and presented the number of them required to seismic rehabilitation objectives. Note: As the coefficient of variation (C.O.V) results are more than 14%, additional tests should be performed so that the coefficient is less than or equal to 14%.

3.2.4.4 Quantitative evaluation of concrete buildings components 3.2.4.4.1 Concrete moment frame Admission requirements of moment connection are the evaluation of the ductility, the stiffness, and the strength of the moment connection (Fig. 3.2.11). 3.2.4.4.1.1 Types of moment frames

• • • • • 1)

Moment frames of beam-column reinforced concrete; Beam-column pretensioned frames; Slab-column moment frames; Precast concrete frames; and Concrete braced frames. Beam-column reinforced concrete moment frames and pretensioned moment frames The main structural components of the frame are beams, columns, and connections. In this case, the presence or absence of the slab does not affect the type of moment frame system. 1. The frame is such that beams and columns together with the connections are the most important components in transferring momentum in the connections.

Figure 3.2.11 Concrete moment frame.

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2. In moment frames of reinforced concrete in type I (beam and column), the main reinforcement in beams and columns are not pretensioned, but in moment frames type II, beam and column are pretensioned. 2) Slab-column moment frames These frames are similar to the moment frames combined column beams except that in this type of slabs, the slabs perform as beams. 3) Precast concrete frames The most significant feature of this frame is the system of separation in beams and columns that are made as separate parts and connected with proper connections (Fig. 3.2.12). 4) Concrete braced frames In these frames, steel or concrete seismic elements are placed as a truss that can withstand seismic load. If these elements are surrounded with masonry infills, the infill criteria provided in this book will also be considered in evaluating performance (Fig. 3.2.13).

Figure 3.2.12 Chart of precast concrete frame types.

Figure 3.2.13 Concrete brace frame.

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3.2.4.4.1.2 Linear analysis and evaluation method for moment frame components

3.2.4.4.1.2.1 Calculation demand capacity ration (DCR) of components The most important step in analyzing and evaluating methods is to assess the ductility need in members and elements. Tables 3.2.2 and 3.2.3 show the classification of the ductility and components efforts need based on the maximum DCR capacity ratio [1,2]. 3.2.4.4.1.2.2 Determining the stiffness of components In structural engineering, the term “stiffness” refers to the rigidity of a structural element. In general terms, this means the extent to which the element is able to resist deformation or deflection under the action of an applied force. In contrast, flexibility or pliability is a measure of how flexible a component is, that is, the less stiff it is, and the more flexible it is. In a structure that is made up of many different structural elements, those elements will carry load proportionate to their relative stiffness. Therefore the load an element will attract increases the stiffer it is. For calculating stiffness of components in reinforced concrete for beam-column, prefabricated beam-column, slab-beam reinforced concrete and prefabricated concrete columns and frames and moment frames we can use Table 3.2.4 (Fig. 3.2.14) [1
3]. Table 3.2.2 Classification of the components ductility demand [1]. Maximum DCR value or ductility ratio The ductility demand

Smaller than 2 Between 2 and 4 Bigger than 4

Low Average High

Table 3.2.3 Controlling components efforts. Deformation controllable— Type of members QCE

Force controlled— QCL

Flexural moment Flexural moment
Flexural moment and shear Flexural moment and shear Flexural moment

Moment frames Beam Column Connections Shear wall Wall Coupling beams Shear wall bearing columns

Shear Section and axial force Shear

Shear and axial force

Table 3.2.4 Determining the stiffness of components [1]. Concrete moment frames of beam and columns with effective slab

Concrete moment frames of beams and columns without effective slab

The infill stiffness of flange and web for flexural and axial forces must be calculated. For this purpose, the width of the effective web on each side should be taken into account. The effective width calculation should be done according to the criteria in the concrete relation codec like American Concrete Institute (ACI). Compression flange The axial and flexural forces are resisted by concrete and reinforces that are placed in the effective width

The values of the stiffness affecting the behavior of components in the linear behavior range (FEMA 356:Table 6.5)

Tension flange

Only longitudinal reinforcements within effective width should be used to calculate flexural and axial strength provided that the reinforcement length of the reinforcement after the critical cross section is sufficient. It is assumed that the part of the wing that is outside the width of the web is not effective in bearing shear force.

Member

Axial rigidity Shear rigidity flexural rigidity

Beam—nonprestressed




Beam—restressed Column with compressive axial Ec Ag load due to gravity load Designed larger than 0:5 Ag fc Column with axial load induced by gravity load design less than 0:3 Ag fc or tensile load Wall without crack Wall with crack Flat slabs—nonprestressed
Flat slabs—restressed

Note: Value for T-shaped beams is equal twice as much Ig for their webs. In shear rigidity (stiffness), concrete shear modulus is 0:4EC .

0:4 Ec AW

0:5 Ec Ig E c Ig 0:7 Ec Ig

0:5 Ec Ig

0:4 Ec Ag

0:8 Ec Ig 0:5 Ec Ig 0:5 Ec Ig

Types of existing buildings: detailed introduction and seismic rehabilitation

315

Figure 3.2.14 Concrete-beam simulation to understand behavior in compressive and tensile under loads [1].

3.2.4.4.1.2.3 Determining components’ strength As mentioned in Chapter 2, Seismic Rehabilitation and Practical Methods in Seismic Rehabilitation of Existing Buildings, the behavior of the components is generally in the two forms of force controlled and deformation controlled. So that, we analyze the behavior and performance of concrete structures in terms of the type of force applied. First, considering the basic criteria for development length and connections are required for any type of seismic system, we will discuss the following. 3.2.4.4.1.2.3.1 Development length and splice of reinforcement The development length for the reinforcement patched shall be checked in accordance with the following criteria (Fig. 3.2.15) [1
3]. 3.2.4.4.1.2.5 Connections 3.2.4.4.1.2.5.1 Place in cast Efforts of members in molded connections,

including shear forces, tensile forces, flexural moment, etc., are considered as force-controlled parameters. Like other force-controlled parameters, the minimum strength is considered as strength capacity. The minimum connection strength shall be calculated on the basis of the final values obtained from the ACI regulations, assuming a coefficient of strength reduction or minor safety coefficients equal to one. The capacity of restraints in areas where the likelihood of cracking is likely to be reduced by half [1
3]. 3.2.4.4.1.2.5.2 Postinstalled Member efforts in postinstalled connection systems are considered to be force controlled. Therefore their minimum strength is considered as their strength capacity. The minimum capacity of braces shall be determined by the value of “average minus one standard deviation” of the final values printed on valid laboratory reports (Fig. 3.2.16).

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Seismic Rehabilitation Methods for Existing Buildings

Figure 3.2.15 Development length and splice of reinforcement. fs , maximum tension on rebar; ld , length required: ACI 318, Ch12 or 21;fy , tension yields to rebar.

Figure 3.2.16 Concrete connection types.

3.2.4.4.1.3 Evaluate the capacity of components in moment frame of beamcolumn reinforced concrete

3.2.4.4.1.3.1 Evaluation of strength for beams in linear limitation 3.2.4.4.1.3.1.1 Flexural strength Mn The flexure in the moment frames of the concrete has a deformation-controlled behavior. In addition, according

Types of existing buildings: detailed introduction and seismic rehabilitation

317

to the criteria, these frames are used when the axial force created in the beams is negligible. Mn flexural strength with or without axial force shall be in accordance with ACI regulations, assuming partial safety coefficients of strength in concrete and steel are equal to one. Strength and deformation capacities of the members shall be calculated by taking into account the development length available for the longitudinal bars in accordance with the criteria set out in the following [1,2]: QCE 5 MCE 5 Mn

(3.2.2)

3.2.4.4.1.3.1.2 Shear and torsion strength Vn Shear and torsion are among

the force-controlled behavior. Vn Is the lower-bound shear strength of the beams, obtained from the following criterion? QCL 5 VCL 5 Vn

(3.2.3)

The transverse reinforcements are effective in shear or torsion tolerances under the 50%. 1. The longitudinal distance of the transverse reinforcement shall be more than half the effective depth of the member involved in the d/2 calculation in the shear direction; 2. In beams and columns where the “transverse reinforcement” stirrup have lap splice or hooks are insufficiently fastened to the concrete core. If the stirrups are within the range of the member with the average ductility need, the 2 # DCR # 4 occurs. 3.2.4.4.1.3.2 Evaluation of strength in columns in linear analysis method In moment ðKip-inÞ, they are deformation controlled and in pressure force, force controlled (Table 3.2.5). " #2   MUDy MUDx 2 1 #1 (3.2.4) mx κMCEx my κMCEy Shear and torsion force: The shear strength of the columns is determined according to the criteria presented in ACI. The following criteria must be taken into account in its ductility. 3.2.4.4.1.3.3 Evaluation of connections in linear limitation 1. For connections in moment frames: The ACI criteria must be taken into account to calculate the shear strength of the connections and the relevant criteria. In connections, with the assumption that the depth of connection is equal to the column dimension in target frame direction

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Seismic Rehabilitation Methods for Existing Buildings

Table 3.2.5 Parameters for evaluating of strength in columns in linear analysis method [1]. Row Parameters Description

1

MUDx

2

MUDy

3

MCEx

4

MCEy

5 6 7

κ mx my

Design bending moment around axis X for axial force PUF, ðKip-inÞ Design bending moment axis design around axis Y for axial force PUF, ðKip-inÞ Expected bending moment strength around axis X with the presence of axial force PUF, ðKip-inÞ Expected bending moment strength around axis Y with the presence of axial force PUF, ðKip-inÞ Knowledge factor Coefficient M column for bending around axis X Coefficient M column for bending around axis Y

as well as width of these connections, the nominal cross-sectional area Aj must be equal to one of the modes in the following [1
3]: a. Column width. b. Beam and connections width plus depth of it. c. Twice the minimum vertical distance between the longitudinal axis of the beam and the side of the column. 2. Pretensioned reinforced concrete frame: Strength evaluation is the same as the strength criteria in concrete-beam flexural frame, and it should be noted that for the effort and parameters of the deformation-controlled response, the pretension effect must be taken into account in determining the maximum response related to nonlinear frame behavior. In the case of force-controlled response attempts and parameters, if a reduction in pretension force occurs, the effects of reduction in pretension force on strength must be considered as a design pattern [1
3]. 3. Slab-column moment frames: Strength evaluation in slab-column moment frames is the same as the strength criteria in column-beam flexural frame. In addition, the strength of slab-column connection must be determined and considered in the analytical model [1
3]. 3.2.4.4.1.3.4 The flexural strength of a slab The required strength in the slab to tolerate the anchor due to lateral deformations is obtained from the following equation and shear strength estimation based on the

319

Types of existing buildings: detailed introduction and seismic rehabilitation

items presented in the column strength evaluation (Section 3.2.4.4.1.3.2) (Table 3.2.6) [1
3]: Mncs 2 Mgcs

(3.2.5)

3.2.4.4.1.3.5 Slab-column connections strength For internal connections without transverse beams and for external connections with a moment perpendicular to the edge of the slab: moment transfer strength is (Table 3.2.7) [1
3]: X Mn =γ f (3.2.6) Muf 5 Moment around parallel axis of slab edge in outer connections without transverse beams. 4. Prefabricated concrete frames equivalent to in-place moment frames: The evaluation of the strength in premade concrete frames equivalent to the inplace moment frames is the same as the strength criteria for the Table 3.2.6 Parameters for evaluating of flexural strength of a slab [1]. Row Parameters Description

Mncs Mgcs

1 2

Flexural strength of column strip design according to ACI Moment of the column strip due to gravitational loads

Table 3.2.7 Parameters for evaluating of slab-column connections strength [1]. Row Parameter Description

1

2

P

Mn

The sum of the positive and negative resistances of a slab between lines that are one and a half times the slab thickness or column thickness of the inscription. pffiffiffiffiffiffiffiffiffiffi γ f 5 1 1 0:66 b1 =b2 Fraction coefficient of moment and b1 , b2 are dimensions related to the critical perforation cutting environment located at a distance ðd=2Þ from the edge of the support. b1 5 in the order of length, b2 5 in the order of width.

Note: if shear at critical section is not caused by gravity loads greater than 0.75 V, or shear in a corner support not more than 0.5 V, the anchor transfer strength can be considered equal to the cross-sectional flexural strength of the slab between the lines with distance C1 outside the column Vc equals to direct puncture shear strength according to ACI regulations.

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Seismic Rehabilitation Methods for Existing Buildings

concrete-beam-columns moment framework. The following criteria should also be taken into account [1,2]: a. Pretension effects. b. Construction order effects. c. Development effective of other components in the frame. 5. Precast concrete moment frames with pin connection: The evaluation of strength in precast concrete moment frames with pin connection is the same as the strength criteria in concrete moment frame. In addition, the criteria related to connections must also be considered in connection strength. 6. Adaptive precast concrete frames that only have a gravitational load-bearing duty: Strength evaluation in adjoining precast concrete frames is similar to strength criteria in concrete moment frame. They must also have sufficient strength and ductility to transfer forces generated from one member to another and to a system designed to withstand lateral loads. 3.2.4.4.1.4 Acceptance criteria

3.2.4.4.1.4.1 Beam-column concrete moment frames 3.2.4.4.1.4.1.1 Beams control by flexural In the following relationship, to control the expected flexure strength of reinforced concrete beams against the flexural moment applied to it, value m is extracted using Table 3.2.8 [1,2]: m k MCE $ MUD

(3.2.7)

Lower-bound shear strength kVCL $ VUF

(3.2.8)

(Fig. 3.2.17) 3.2.4.4.1.4.1.2 Column control In flexural control: In uniaxial flexure control,

the ðPUF =KAg fC Þ relationship indicates that the flexural effort must be less than the expected flexure strength in the column according to Eq. (3.2.7). Double-axis flexure control: Member control is achieved using Eq. (3.2.4) (Fig. 3.2.18) [1
3]: In shear control: As mentioned earlier, the lower-bound shear strength of reinforced concrete columns was corrected and evaluated using the ductility coefficients presented in the tables in this chapter. All members such as primary and secondary are modeled in the relevant balance and average DCR values are rechecked. If the DCR value for vertical components is greater than the average value for horizontal components in that

321

Types of existing buildings: detailed introduction and seismic rehabilitation

Table 3.2.8 Numerical acceptance criteria for linear procedures—reinforced concrete beams [1]. Conditions

IO

Components type Primary

0

ρ2ρ ρbal

# 0/0 # 0/0 $ 0/5 $ 0/5 # 0/0 # 0/0 $ 0/5 $ 0/5 Beams

Transverse reinforcent C C C C NC NC NC NC -controlled by shear

Vpffiffiffi bw d fc

#3 $6 #3 $6 #3 $6 #3 $6

5

Secondary

LS

CP

LS

CP

6 3 3 2 3 2 3 2

7 4 4 3 4 3 3 2

6 3 3 2 3 2 3 2

10 5 5 4 5 4 4 3

1.75 1.75

3 2

4 3

3 2

4 3

3

4

2V Vc

3 2 2 2 2 1/25 2 1/25

The distance of the stirrups # d=2 1.25 1.5 The distance of the stirrups . d=2 1.25 1.5 Beams controlled by inadequate or splicing along the span

The distance of the stirrups . d=2 1.25 1.5 1.75 The distance of the stirrups . d=2 1.25 1.5 1.75 Beam controlled by inadequate embedment beam-column connections 2

2

3

Figure 3.2.17 An example of concrete-beam damage.

alignment and is greater than the building shall be nonlinear reanalyzed (Table 3.2.9) [1,2]. 3.2.4.4.1.4.1.3 Connections In linear analysis methods, all of the primary junctions are considered as force controlled and the coefficients m is not used for them, but if the connections are secondary, they can be

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Seismic Rehabilitation Methods for Existing Buildings

Figure 3.2.18 An example of concrete column damage.

Table 3.2.9 Numerical acceptance criteria for linear procedures—reinforced concrete columns [1]. Conditions

IO

Components type Primary

Column control by flexure P=Ag f 0c Transverse reinforcement 0/1 # C 0/1 # C 0/4 $ C 0/4 $ C 0/1 # NC 0/1 # NC 0/4 $ NC 0/4 $ NC Column control by shear

Secondary

LS

CP

LS

CP

3 2.4 2 1.6 2 1.6 1.5 1.5

4 3.2 3 2.4 3 2.4 2 1.75

4 3.2 3 2.4 2 1.6 1.5 1

5 4 4 3.2 3 2.4 2 1.6

Vpffiffiffi bw d fc

3# 6$ 3# 6$ 3# 6$ 3# 6$

2 2 1.25 1.25 2 2 1.25 1.25

Hoop spacing or # d=2 ðP=Ag fg Þ # 0:1


2 3 Other cases


1.5 2 Columns controlled by inadequate development or splicing along the clear height Hoop spacing or # d=2 . d=2 Hoop spacing Columns with axial loads exceeding 0.70Po

1.25


1.5


1.75


3 2

4 3

At all lengths, the strictures are eligible Other cases

1


1


2


2 1

2 1

In case in flexural plastic hinge area in a member, the distance stirrup are less than or equal to ðd=3Þ. In addition, for members with average to high ductility need, the provide strength by stirrup (Vs) should be at least equal to (0.75). In this case, it is the qualified member (C). Otherwise, it is not a qualified member (NC).

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Types of existing buildings: detailed introduction and seismic rehabilitation

considered as deformation controlled. In Table 3.2.10, P is the axial force of the design for the column above the connections, and Ag is the crosssectional area of the entire connections. The shear force V is the design and shear strength of the connections Vn (Fig. 3.2.19) [1,2]. Table 3.2.10 Numerical acceptance criteria m for linear procedures—reinforced concrete-beam-column [1]. Conditions IO Components type

A. interior joint Transverse reinforcement P=Ag fc # 0/1 C # 0/1 C $ 0/4 C $ 0/4 C # 0/1 NC # 0/1 NC $ 0/4 NC $ 0/4 NC

Primary

secondary

LS

CP

LS

CP

V =Vn 1.2 # $ 1.5 1.2 # 1.5 $ 1.2 # 1.5 $ 1.2 # 1.5 $































3 2 3 2 2 2 2 2

4 3 4 3 3 3 3 3

V =Vn # 1.2 $ 1.5 # 1.2 $ 1.5 # 1.2 $ 1.5 1.2 # $ 1.5































3 2 3 2 2 2 1.5 1.5

4 3 4 3 3 3 2 2

Other connections

P=Ag fc # 0/1 # 0/1 $ 0/4 $ 0/4 # 0/1 # 0/1 $ 0/4 $ 0/4

Transverse reinforcement C C C C NC NC NC NC

Figure 3.2.19 An example of concrete connection damage.

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Seismic Rehabilitation Methods for Existing Buildings

3.2.4.4.1.4.2 Slab-column moment frame 1. In the primary flexural members of slab and column, shear transfer and anchor in slab-column connections are among the deformationcontrolled efforts. In secondary members, the deformation-controlled efforts for shear and retrofit. The reinforcement is examined according to the table below. Also, the criteria for the weak column in the weak floor should be evaluated in accordance with the section of concrete column-beam moment frame [1,2]. Vg is critical slab shear due to gravity forces and Vo is strength against direct penetrating shear in Table 3.2.11 (Fig. 3.2.20) [1
3]. 3.2.4.4.1.4.3 Precast moment frame The acceptance criteria for these types of frames are the same as the criteria for moment frames and beams. 3.2.4.4.1.5 Nonlinear analysis and evaluation method (static and dynamic) for moment frame components

3.2.4.4.1.5.1 Determination of stiffness of components In the nonlinear method, the force and deformation curves are used. In this case, the values of a, b, c are extracted from Table 3.2.12. Deformation diagram (A), in this curve, deformations are expressed directly using terms such as strain, curvature, rotation, or elongation. Deformation ratio diagram (B), in this curve, deformations are expressed in terms such as shear angle and tangential drift ratio (Fig. 3.2.21) [1,2]. Table 3.2.11 Numerical acceptance criteria for linear procedures—two-way slabs and slab-column connections [1]. Conditions IO Components type Primary LS

A. flexure-controlled slabs and slab-column connections Continuity Reinforcement3 Vg =Vo 0/2 # Yes 2 2 0/4 $ Yes 1 1 0/2 # No 2 2 0/4 $ No 1 1

secondary CP

LS

CP

3 1 3 1

3 2 2 1

4 3 3 1

B. Slabs controlled by inadequate development or splicing along the span


3

4

Slabs controlled by inadequate embedment into slab-column joint

2

2

3

3

4

Types of existing buildings: detailed introduction and seismic rehabilitation

325

Figure 3.2.20 An example of concrete slab-column punching damage.

Table 3.2.12 Description nonlinear force-deformation analysis curve area.

Linear relation

A Member cannot bearing load B An effective yielding point Between B and C There is a reduced linear stiffness From C to D Sudden decline in lateral strength From D to E Remains constant After E Eventually the strength drops to zero at this point

Figure 3.2.21 Nonlinear force-deformation analysis curve.

3.2.4.4.1.5.2 Determination of strength of components 3.2.4.4.1.5.2.1 Nonlinear static method Expected strength values QCE, and lower-bound strength QCL, for concrete structural components are determined according to the criteria specified for the linear analysis method of evaluation for members’ strength [1,2].

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Seismic Rehabilitation Methods for Existing Buildings

Strength evaluation tips include • Determining the strength of each component based on the values of the deformation- and shear-controlled behavior, similar to the methods presented in the analysis and linear behavior range. • The expected strength is considered for the deformation-controlled components. • The minimum strength is used for force-controlled components. Note: The knowledge factor for new components is always considered equal to 1 [1,2]. 3.2.4.4.1.5.2.2 Nonlinear dynamic method In this method, the strength and deformation of the concrete members should be based on the values obtained from the earthquake loading including the reciprocating cycle to the displacement target. 3.2.4.4.1.5.3 Acceptance criteria The values of the deformations and forces of the deformation-controlled and force-controlled components are calculated through nonlinear analysis of the elements. In components with deformation-controlled behavior, the deformations resulting from the analysis must be smaller than the permitted deformation in the tables presented for the selected performance level. Since in nonlinear methods the calculated effort and response are evaluated based on the plastic hinge rotational capacities of the beams and columns, the tables presented for beams and columns and column-beam connections for shear deformation are presented [1,2]. 3.2.4.4.1.5.3.1 Moment frame of beam-column reinforced concrete

3.2.4.4.1.5.3.1.1 Beams Since the flexure performance of the beams is in the range of nonlinear deformation-controlled behavior, results are obtained Table 3.2.13 (Fig. 3.2.22) [1,2]. 3.2.4.4.1.5.3.1.2 Column In case the columns are the primary members, if the design shears calculated are greater than the design shear strength, the permissible deformation of the plastic hinges for the CP collapse performance level shall not exceed the deformation that, according to the calculations, results in shear strength. In addition, the permissible deformation for the level of life safety (LS) performance shall not be greater than three-fourths the value of the corresponding shear strength. In addition, performance should be considered inadmissible if the numbers listed in the table are obtained for performance or the there is no elastic behavior is resulted for members. Therefore seismic performance is evaluated using

327

Types of existing buildings: detailed introduction and seismic rehabilitation

Table 3.2.13 Numerical acceptance criteria for nonlinear procedures—reinforced concrete beams [1]. Conditions

Modeling parameters

Plastic rotation angle, radians

Plastic rotation

Performance level

Residual strength ratio

Component type IO

a

Primary

Secondary

LS

CP

LS

CP

0.02 0.01 0.01 0.005 0.01 0.005 0.01 0.005

0.025 0.02 0.02 0.015 0.02 0.01 0.01 0.005

0.02 0.02 0.02 0.015 0.02 0.01 0.01 0.005

0.05 0.04 0.03 0.02 0.03 0.015 0.015 0.01

b

c

0.05 0.04 0.03 0.02 0.03 0.015 0.015 0.01

0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2

0.01 0.005 0.005 0.005 0.005 0.015 0.005 0.015

0.2 0.2

0.0015 0.002 0.003 0.01 0.02 0.0015 0.002 0.003 0.005 0.01

Beams controlled by flexure1 ρ 2 ρ0 ρbal

# 0.0 # 0.0 $ 0.5 $ 0.5 # 0.0 # 0.0 $ 0.5 $ 0.5

Trans. Reinf. C C C C NC NC NC NC

Vpffiffi bw d fc

3# 6$ 3# 6$ 3# 6$ 3# 6$

0.025 0.02 0.02 0.015 0.02 0.01 0.01 0.005

Beams controlled by shear

Stirrup spacing # d/2 Stirrup spacing . d/2

0.003 0.02 0.003 0.01

Beams controlled by inadequate development or splicing along the span

Stirrup spacing # d/2 Stirrup spacing . d/2

0.003 0.02 0.003 0.01

0.0 0.0

0.0015 0.002 0.003 0.01 0.02 0.0015 0.002 0.003 0.005 0.01

Beams controlled by inadequate embedment into beam-column joint

0.015 0.03

0.2

0.01

0.01

0.015 0.02

0.03

Figure 3.2.22 A view of the wrong reinforcement in concrete beams.

other values and methods that have been confirmed by analysis or laboratory evidence (Fig. 3.2.23 and Table 3.2.14) [1,2]. 3.2.4.4.1.5.3.1.3 Connections A concrete structure may not be vulnerable to columns and beams in terms of capacity and acceptance criteria, but

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Seismic Rehabilitation Methods for Existing Buildings

Figure 3.2.23 Nonlinear force-deformation analysis curve.

Table 3.2.14 Numerical acceptance criteria for nonlinear analysis—reinforced concrete columns [1]. Conditions

Modeling parameters

Plastic rotation angle, radians

Plastic rotation

Performance level

Residual strength ratio

Component type IO

a

column controlled by flexure Vpffiffiffi Trans 5 2V Vc b d f reinf. w c # 0.1 C 3# 0.02 # 0.1 C 6$ 0.016 $ 0.4 C 3# 0.015 $ 0.4 C 6$ 0.012 # 0.1 NC 3# 0.006 # 0.1 NC 6$ 0.005 $ 0.4 NC 3# 0.003 $ 0.4 NC 6$ 0.002

b

c

0.03 0.024 0.025 0.02 0.015 0.012 0.01 0.008

0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2

Primary

Secondary

LS

CP

LS

CP

0.015 0.012 0.012 0.01 0.005 0.004 0.002 0.002

0.02 0.016 0.015 0.012 0.006 0.005 0.003 0.002

0.02 0.016 0.018 0.013 0.01 0.008 0.006 0.005

0.03 0.024 0.025 0.02 0.015 0.012 0.01 0.008

P Ag f 0c

0.005 0.005 0.003 0.003 0.005 0.005 0.002 0.002

Columns controlled by shear All cases Columns controlled by inadequate development or splicing along Hoop spacing # d/2 0.01 0.02 0.4 0.005 0.005 Hoop spacing $ d/2 0 0.01 0.2 0 0 Columns with axial loads exceeding 0.70Po Conforming hoops over the 0.015 0.025 0.02 0 0.005 entire length All other cases 0 0 0 0 0

0.003 0.004 the clear height 0.01 0.01 0.02 0 0.005 0.01 0.01

0.01

0.02

0

0

0

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Types of existing buildings: detailed introduction and seismic rehabilitation

a lack of careful consideration of acceptance criteria in its connection can lead to significant damage. Therefore, the study of acceptance criteria for connections plays an important role in the seismic rehabilitation process. Using the specifications and parameters provided in the Table 3.2.15, acceptance criteria for connections are available. Also in the Fig. 3.2.24, show an example of a weakness in the connections, which eventually led to the collapse (CP) performance level of the structure, which did not have any problems in (LS) life safety performance level of beams and columns.

Table 3.2.15 Numerical acceptance criteria for nonlinear, reinforced concrete-beamcolumn joints (connections) [1]. Conditions

Modeling parameters

Plastic rotation angle, radians

Plastic rotation

Performance level

Residual strength ratio

Component type IO

Primary

Secondary

LS

CP

LS

CP

a

b

c

0.015 0.015 0.015 0.015 0.005 0.005 0.005 0.005

0.03 0.03 0.025 0.02 0.02 0.015 0.015 0.015

0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2

0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

0.02 0.015 0.015 0.015 0.015 0.01 0.01 0.01

0.03 0.02 0.025 0.02 0.02 0.015 0.015 0.015

0.01 0.01 0.01 0.01 0.005 0.005 0.0 0.0

0.02 0.015 0.02 0.015 0.01 0.01 0.0 0.0

0.2 0.2 0.2 0.2 0.2 0.2



0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

0.015 0.01 0.015 0.01 0.0075 0.0075 0.005 0.005

0.02 0.015 0.02 0.015 0.01 0.01 0.0075 0.0075

Interior joints (connections) P Ag f 0c

# 0.1 # 0.1 $ 0.4 $ 0.4 # 0.1 # 0.1 $ 0.4 $ 0.4

Trans reinf. C C C C NC NC NC NC

V Vn

# 1.2 $ 1.5 # 1.2 $ 1.5 # 1.2 $ 1.5 # 1.2 $ 1.5

Other joints (connections) P Ag f 0c

# 0.1 # 0.1 $ 0.4 $ 0.4 # 0.1 # 0.1 $ 0.4 $ 0.4

Trans reinf. C C C C NC NC NC NC

V Vn

# 1.2 $ 1.5 # 1.2 $ 1.5 # 1.2 $ 1.5 # 1.2 $ 1.5

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Seismic Rehabilitation Methods for Existing Buildings

3.2.4.4.1.5.3.2 Slab-column moment frame In the primary members of

moment in slabs and columns and shear and in slab-column connections are among the deformation-controlled efforts. In secondary members, deformation-controlled efforts for shear and development length of rebar are as described in Table 3.2.16. In addition, the criteria for the weak column in the weak floor should be evaluated in accordance with the section of beam-column concrete moment frames (Fig. 3.2.25) [1,2].

Figure 3.2.24 The loss of connection capacity has led to the demolition of buildings during the earthquake. Table 3.2.16 Numerical acceptance criteria for nonlinear procedures, two-way slabs and slab-column connections [1]. Conditions

Modeling parameters

Plastic rotation angle, radians

Plastic rotation

Performance level

Residual strength ratio

Component type IO

a

b

c

Primary LS

Secondary CP

LS

CP

0.03 0.03 0.015 0.0

0.05 0.04 0.02 0.0

0.01

0.02

0.02

0.03

Slabs controlled by flexure, and slab-column connections1 Vg Continuity Reinforcement Vo

# 0.2 Yes 0/4 $ Yes 0/2 # Yes 0/4 $ Yes Slabs controlled

0.02 0.05 0.2 0.01 0.015 0.02 0.0 0.04 0.2 0.0 0.0 0.0 0.02 0.02
0.01 0.015 0.02 0.0 0.0
0.0 0.0 0.0 by inadequate development or splicing along the span 0.0 0.02 0.0 0.0 0.0 0.0 Slabs controlled by inadequate embedment into slab-column joint 0.015 0.03 0.2 0.01 0.01 0.015

Types of existing buildings: detailed introduction and seismic rehabilitation

331

Figure 3.2.25 Slab-column moment frame structure.

Figure 3.2.26 Precast moment frame.

1. “Yes” in bounding bars shall apply when at least one of the main lower bars in each direction is effectively extended in the column. 3.2.4.4.1.5.3.3 Precast moment frame The acceptance criteria for these types of frames are the same as the criteria for moment frames (Fig. 3.2.26) [1,2]. 3.2.4.4.2 Concrete shear walls and concrete frame with infill Studying methods of analysis of concrete frames with infill wall In modeling such frames, the probability of any of the following failures should be taken into account [1,2]: 1. Failure due to flexure. 2. Failure due to shear. 3. Failure due to inadequate braced length of rebar. 4. Failure due to insufficient length of rebar splice. 5. Failure caused by breakage at any point.

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Seismic Rehabilitation Methods for Existing Buildings

Figure 3.2.27 Analysis and evaluation of concrete infill frames in concrete building.

6. Failure due to interaction with other nonstructural components (Fig. 3.2.27). 3.2.4.4.2.1 Modeling of concrete frames with reinforced infill frames

Concrete infill frames must be fully and appropriately modeled considering deformation capacity, stiffness, and strength in all elements including beams, columns and slabs, frame connections with concrete infill frames. Generally, if the frame has a flexible function, for surfaces with relatively low deformation, the structure including the enclosed frame and the infill frame can be modeled as an equivalent shear wall in the modeling, and in other cases, the reinforced concrete infill may be modeled as masonry infill frames like diagonal elements in modeling. If the frame is flexible and the deformations are low. The frame and infill are considered as environmentally homogeneous and an integrated such as shear wall [1,2]. 3.2.4.4.2.2 Types of reinforced concrete shear wall

If the frame is able to stay stable after the masonry material's infill strength decreases, restrictions on the performance level of collapse threshold for the infill should not be applied. 3.2.4.4.2.2.1 In-place shear wall In this type of shear wall, to maintain the uniformity and consistency of the wall rebar, it is hooked to the perimeter frame and also the wall and its perimeter frame are integrated seamlessly. The two types of these walls are: couple shear walls and inconsistent shear walls (Fig. 3.2.28) [1,2]. 3.2.4.4.2.2.2 Precast shear wall In prefabricated shear walls, uniformity and consistency are achieved by providing trapezoidal margins along the edges of the panel or by connecting the panels to the frame by steel fasteners. They are subject to the following forces [1,2]: • Variable shear force whose value is at maximum base.

Types of existing buildings: detailed introduction and seismic rehabilitation

333

Figure 3.2.28 In-place shear wall.

Figure 3.2.29 Precast shear wall.

•

Variable flexural moment which is again maximum heel of wall and creates stretch on one edge (the edge is close to the forces and the pressure on the reciprocating edge). Regarding the possibility of change in direction of wind or earthquake force in the building, stretch must be considered both edges of the wall. • The axial force of compression due to the weight of the floors resting on the shear wall (Fig. 3.2.29). Note: If the shear wall height is low, the design will often be based on shear strength. However, if the shear wall height is high, the design will be based on the flexural moment. In any case, the wall must be controlled and armed against both forces. 3.2.4.4.2.3 Static and dynamic linear method

3.2.4.4.2.3.1 Determining stiffness of components The effective stiffness of all members forming the frame and shear wall is determined by their material characteristics, member dimensions, reinforcement amount,

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Seismic Rehabilitation Methods for Existing Buildings

boundary circumstances as well as the current state of the member in terms of tension level and cracking condition (Table 3.2.17) [1,2]. Tip: The effective stiffness of the columns on which the inconsistent shear walls relies on, for the loading direction, can lead to tension or pressure. Also, connections between the shear walls and the frame members may model as rigid components. 3.2.4.4.2.3.2 Determining strength of components Nominal flexural strength of shear walls or wall parts, Mn , shall be calculated in accordance with the criteria set forth in the ACI regulations, assuming partial safety coefficients equal to one. In calculating the nominal flexural strength, the effective widths of compression and tensile wings according to ACI can be used (Table 3.2.18). (3.2.9) φ 5 1-QCE 5 MCE 5 Mn To determine the flexural strength of the shear wall, in point B of the Fig. 3.2.32, only the longitudinal bars located at the boundary member must be taken into account. If the wall does not have boundary members, only the bars at the bottom 25% of the infill frame are considered in the yield strength calculation. To calculate the nominal flexural strength of a wall specified by point C, all longitudinal bars (including web bars) must be taken into account [1,2]. 3.2.4.4.2.3.3 Nominal shear strength of shear walls According to the “twentieth chapter” of the ACI Code, the nominal shear strength of Table 3.2.17 The values of the stiffness affecting the behavior of components in the linear behavior range. Member Axial stiffness Shear stiffness Flexure stiffness

Shear wall without crack Shear wall with crack

Ec A g Ec A g

0/4 Ec Aw 0/4 Ec Aw

0/8 Ec Ig 0/5 Ec Ig

Table 3.2.18 Determining strength of components of shear wall.

be d HW

Minimum effective width of the flange for the walls with L and T cross sections resulted from the relationships Useful distance to adjacent wall The total height of the wall

be # 0:5ðdÞ be # 0:1 HW

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Types of existing buildings: detailed introduction and seismic rehabilitation

columns Vn that endure inconsistent shear walls must also be determined (Fig. 3.2.30, Tables 3.2.19 and 3.2.20). φ 5 1-QCL 5 VCL 5 Vn

(3.2.10)

3.2.4.4.2.3.4 Acceptance criteria for components Control by flexural must be considered. The required parameters are obtained from ACI 318 and in this case criteria for column is equal hoops over the entire length of the column at a spacing # d=2 and VS by stirrup(hoops) must be

Figure 3.2.30 Couple beam in shear walls. Table 3.2.19 Calculation of the contribution of horizontal bars to shear strength.

The shear strength of the wall can be calculated according to the ACI code The contribution of the wall bars to the constant shear strength and equal to the resulting value can be obtained from 5 0/0015 ρH Table 3.2.20 Controlling primary component efforts. Deformation controlled QCE Member type

Shear wall Flexural moment and shear Wall Flexural moment and shear anchor Couple beams Flexural moment Shear wall bearing columns

0:0015 # ρH # 0:0025 ρH # 0:0015

Force controlled QCL



Shear and axial force

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Seismic Rehabilitation Methods for Existing Buildings

higher than or equal to the column. For beam strip spacing # d=3 and strip strength VS is less than 0.75 shear strength of coupling beam. If secondary coupling beams length is less than 8 (in.), we can multiply the values of Table 3.2.21 by 2 times [1
3]. Control by shear: Must be considered the axial force of the member shall be less than or p equal to 0:15 Ag fc and maximum shear tension shall ffiffiffiffiffi 0 be less or equal to 6 f C . Otherwise, bending is assumed to be a forcecontrolled response parameter. Other criteria limitation like control by flexural (Table 3.2.22) [1
3]. 3.2.4.4.2.4 Static and dynamic nonlinear analysis method

3.2.4.4.2.4.1 Determining stiffness of components The total forcedeformation relationship for the analytical models of shear walls, wall elements, coupling beam beams, and columns on which the discontinuous shear walls rely must be in accordance with the following general relation (Fig. 3.2.31 and Table 3.2.23).   My θy 5 (3.2.11) lp Ec I In analytical models of shear walls and wall components, if the value 1p is equal to half of the wall length in plan or height of ground floor, any of them which is less, for the columns that support inconsistent shear walls, the value of 1p is considered less than effective bending depth of the component. In shear walls where the function is shear-controlled or short shear walls, the relative displacement of the floor is similar to Fig. 3.2.32 [1,2]. 3.2.4.4.2.4.2 Coupling beams Coupling beam is a lateral force resistant component of a structure. Types, advantages and design of coupling beam as per ACI 318-11 is discussed. Coupling beam is used effectively when two shear wall or any other elements that are used for withstanding lateral loads is combined (Fig. 3.2.33) [1,2]. 3.2.4.4.2.4.3 Nonlinear dynamic method In the nonlinear dynamic method, the complete cyclic behavior of each member must be modeled with the help of the characteristics obtained through valid experiments. The total force-deformation relation shown in the shapes is used as the push relationship in the analysis. 3.2.4.4.2.4.3.1 Determining components strength The same rules apply to linear behavior in the analysis.

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Types of existing buildings: detailed introduction and seismic rehabilitation

Table 3.2.21 Numerical acceptance criteria for linear analysis, members controlled by flexure [1]. Conditions m-Factors Performance level IO

Component type Primary

Primary

LS

CP

LS

CP

4 3 3 2 2.5 2 1.5 1.5

6 4 4 2.5 4 2.5 2 1.75

6 4 4 2.5 4 2.5 2 1.75

1 1

1.5 1

2 1









3# 6$

2 1.5

4 3

6 4

6 4

9 7

3# 6$

1.5 1.2

3.5 1.8

5 2.5

5 2.5

8 4




2

5

7

7

Shear walls and wall segments

½As 2 A0s fy 1 P t w lw fc

# 0.1 # 0.1 $ 0:25 $ 0:25 # 0.1 # 0.1 $ 0:25 $ 0:25

shear pffiffi t w lw fc

# 3 $6 # 3 $6 # 3 $6 # 3 $6

Confined boundary1 Yes Yes Yes Yes No No No No

2 2 1.5 1.25 2 1.5 1.25 1.25

8 6 6 4 6 4 3 2

Columns supporting discontinuous shear walls

Transverse reinforcement2 Conforming Nonconforming Shear wall coupling beams4

Longitudinal reinforcement and transverse reinforcement3 Conventional longitudinal reinforcement with conforming transverse reinforcement Conventional longitudinal reinforcement with nonconforming transverse reinforcement Diagonal reinforcement

Shear pffiffi t w lw fc

10

Table 3.2.22 Numerical acceptance criteria for linear procedures—members controlled by shear force [1]. Conditions IO M-Factor Performance level Primary

Secondary

LS

CP

LS

CP

2

2

3

2

3

3# 6$ 3#

1.5 1.2 1.5

3 2 2.5

4 2.5 3

4 2.5 3

6 3.5 4

6$

1.25

1.2

1.5

1.5

2.5

Shear walls and wall segments

All shear walls and wall segments1 Shear wall coupling beams3

Longitudinal reinforcement and transverse reinforcement2 Conventional longitudinal reinforcement with conforming transverse reinforcement Conventional longitudinal reinforcement with nonconforming transverse reinforcement

Shear pffiffiffi tw lw f 0c

Types of existing buildings: detailed introduction and seismic rehabilitation

339

Figure 3.2.31 Beam rotation under inertial flexural moment. Table 3.2.23 Determining stiffness of components for concrete shear wall in nonlinear analysis method. Row Parameter Description

1 2 3 4

My Ec I Lp

Flexure capacity led to shear wall or part of wall Elasticity coefficient Inertial flexural moment in concrete component Assumed length for plastic connection

Figure 3.2.32 Wall deformation and force-deformation curve.

Figure 3.2.33 Coupling beam deformation and force-deformation curve.

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Seismic Rehabilitation Methods for Existing Buildings

3.2.4.4.2.4.3.2 Component acceptance criteria The criteria for acceptance in

nonlinear behavior are not such that the rotational capacity of the plastic connection for flexural and shear deformation of the members is presented in Tables 3.2.24 and 3.2.25. The additional criteria considered in the linear acceptance criterion also apply to columns and beams in nonlinear method [1,2]. 3.2.4.4.3 Foundation Foundation analysis is one of the challenging parts of seismic rehabilitation. Different assumptions with regard to better support conditions, soil properties, location, and type of probable nonlinear behavior lead to wide variation in results. For many buildings, assessing preliminary results to understand how the base interacts with the main structure and the surrounding soil under earthquake loading requires more detailed modeling and analysis. Usually, yield of a foundation or soil member is the foremost mechanism of collapse, but it is only after looking at the main structure and the substructure as a whole system that one can determine the sequence and the behavioral nature of the member. If the logical analysis indicates that new foundations need to be added or existing ones should be modified, the structural engineer must have a good understanding of soil engineering problems, targets of building performance level, performance recommendations, assumptions, methods and operating constraints limitation. It is clear that it is much more difficult to rehabilitate an existing structure than to implement a new one. Adding or complementing is common for new members, like shear walls and braced frames, which are supplemented to main structure in seismic rehabilitation, but seismic rehabilitation of existing foundation without rehabilitation of main structure is paid less attention. There are two main reasons for this [1,2]: 1. Foundation rehabilitation of existing building is very expensive. 2. According to earliest studies of earthquake damage, a relatively small number of casualties have been recognized as results of foundation failure. 3.2.4.4.3.1 General objectives of seismic rehabilitation of foundation

The purpose of any seismic assessment is to identify the deficiencies, the relative probability of their occurrence, and the following risks. During these assessments, the foundation should not be overlooked and the foundation behavior response should be considered in the context of the overall behavior of the building. If the foundation is identified as a weak

Table 3.2.24 Modeling parameters and admission criteria for nonlinear flexure-controlled [1]. Conditions Plastic hinge Residual Acceptable plastic hinge rotation (radians) rotation strength Performance level (radians) ratio IO Component type

Shear walls and wall segments shear ½As 2 A0s fy 1 P pffiffi Confined t w lw fc t w lw fc boundary # 0.1 3# Yes # 0.1 6$ Yes $ 0.25 3# Yes $ 0.25 6$ Yes # 0.1 3# No # 0.1 6$ No $ 0.25 3# No $ 0.25 6$ No

a

b

C

0.015 0.010 0.009 0.005 0.008 0.006 0.003 0.002

0.020 0.015 0.012 0.010 0.015 0.010 0.005 0.004

0.75 0.40 0.60 0.30 0.60 0.30 0.25 0.20

0.010 0.0

0.015 0.0

0.20 0.0

Primary LS

CP

Secondary LS CP

0.005 0.00 0.003 0.0015 0.0022 0.002 0.001 0.001

0.010 0.008 0.006 0.003 0.004 0.004 0.002 0.001

0.015 0.010 0.009 0.005 0.008 0.006 0.003 0.002

0.015 0.010 0.009 0.005 0.008 0.006 0.003 0.002

0.020 0.015 0.012 0.010 0.015 0.010 0.005 0.004

0.003 0.0

0.007 0.0

0.010 0.0









Columns supporting discontinuous shear walls

Transverse reinforcement2 Conforming Nonconforming Shear wall coupling beams

Longitudinal reinforcement and

shear pffiffi t w lw fc

(Continued)

Table 3.2.24 (Continued) Conditions

Plastic hinge rotation (radians)

Residual strength ratio

Acceptable plastic hinge rotation (radians) Performance level IO

transverse reinforcement3 Conventional longitudinal reinforcement with conforming transverse reinforcement Conventional longitudinal reinforcement with nonconforming transverse reinforcement Diagonal reinforcement

Component type Primary LS

CP

Secondary LS CP

0.010 0.005

0.02 0.010

0.025 0.020

0.025 0.020

0.050 0.040

0.50 0.25

0.006 0.005

0.012 0.008

0.020 0.010

0.020 0.010

0.035 0.025

0.80

0.006

0.018

0.030

0.030

0.050

a

b

C

3# 6$

0.025 0.02

0.050 0.040

0.75 0.50

3# 6$

0.020 0.010

0.035 0.025




0.030

0.050

343

Types of existing buildings: detailed introduction and seismic rehabilitation

Table 3.2.25 Numerical acceptance criteria for nonlinear procedures—members controlled by shear [1]. Conditions

Total drift ratio (%), or chord rotation (radians)

Residual strength ratio

d

e

C

2.0

0.4

Shear walls and wall segments All shear walls and wall 0.75 segments Shear wall coupling beams4 shear pffiffiffi0 Longitudinal reinforcement and tw lw fc transverse reinforcement 3# Conventional 6$ longitudinal reinforcement with conforming transverse reinforcement 3# Conventional longitudinal reinforcement with nonconforming transverse reinforcement 6$

Acceptable total drift (%) or chord rotation (radians) Performance level IO

0.4

Component type Primary Secondary LS

CP

LS

CP

0.6

0.75

0.75

1.5

0.002 0.030 0.60 0.016 0.024 0.30

0.006 0.015 0.020 0.020 0.030 0.005 0.012 0.016 0.016 0.024

0.012 0.025 0.40

0.006 0.006 0.010 0.010 0.020

0.008 0.014 0.20

0.004 0.004 0.007 0.007 0.012

member, the type of foundation mechanism must be diagnosed. The issues related to the foundation are indispensable elements of any seismic rehabilitation procedure of building. The behavioral response of the building may be altered by rehabilitation of the main structure in a way that lead to elimination of undesirable modes of foundations. If the operation on the foundation is inevitable, the targets of building performance level include providing strength, stiffness, and adequate deformability to bear pressure, tensions and lateral loads, a well-defined and flexible mechanism for energy dissipation and minimization of the redistribution of gravitational tensions in the existing foundation is required. Foundation rehabilitation of existing buildings is difficult to execute and usually affect systems and procedures. These difficulties are listed below [1,2].

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Seismic Rehabilitation Methods for Existing Buildings

3.2.4.4.3.2 Access and height restrictions

Delicate foundations, such as single foundations or ties, are usually performed with manual methods or small drilling equipment and are rarely problematic. However, their implementation requires more time than that of new buildings. Nevertheless, the implementation of deep foundations has many executive restrictions. Drilling equipment for pier foundations, for example, is more efficient when it is bigger. Moving drilling equipment into a building may require enlarging existing openings. While, usually inside floor height significantly limits the size of drilling equipment that can be used. Drilling adjacent to the walls may limit the size of the pier foundation or move it into the wall and lead to such an eccentricity that needs to be considered [1,2]. 3.2.4.4.3.3 Restrictions due to existing mechanical installations

Most buildings have installations located below ground level or slab levels whose location and depth may not be completely clear. Drilling below ground level requires caution and is usually done manually to avoid damaging installations. Restrictions on maintenance of building operation like seismic rehabilitation of the main structure. If the building is occupied by residents or equipment, foundation demolition, drilling, and excavation operation should be carried out with appropriate coordination. 3.2.4.4.3.4 Different types of foundations

According to the issues presented in the seismic rehabilitation guidelines, foundations are divided into two main categories and foundations are determined in terms of geometry according to Fig. 3.2.34. In this chapter, due to the heights of foundation, they will be divided into two main types of shallow and deep foundation. Features of these types of main foundation caused them to be divided to several types [1,2]. 3.2.4.4.3.4.1 Foundation condition (shallow foundation) In foundation seismic rehabilitation studies, dimensions, shape, location, depth, and

Figure 3.2.34 Chart of foundation types.

Types of existing buildings: detailed introduction and seismic rehabilitation

345

placement of the foundation in general represent the general conditions of the foundation. The characteristics of the adjacent structures in terms of the placement level of the foundation, the type of foundation, and the number of floors are part of the geometric conditions of the foundations. 3.2.4.4.3.4.1.1 Structural conditions of foundation The conditions of foundation structures are the type of foundation structure, the type of materials used, the precise design details, and the type of foundation structure. 3.2.4.4.3.4.1.2 Geotechnical conditions To evaluate wake behavior in geotechnical conditions, minimum information should be collected including permissible load-bearing capacity and ultimate load carrying capacity of soil, type and behavior-related deformation coefficients of soil, and investigating soil lateral pressure on retaining walls. This information is collected on the basis of previous records and reports, local surveys, results of drilling and sampling operations, and field and laboratory tests. Determining the tests required for different seismic rehabilitation objectives are described in Table 3.2.26 according to the condition of present information [1,2]. The minimum number of tests to obtain the information of the structure of the foundation for quantitative evaluation at different levels of performance is in Table 3.2.27. 3.2.4.4.3.4.1.3 Foundation strength and stiffness If in rehabilitation studies it is necessary to investigate the interaction between soil and structures, the strength and stiffness parameters of the foundation of the building should be evaluated. 3.2.4.4.3.4.1.4 Load-bearing capacity of foundations The load-bearing capacity of foundation in the rehabilitate and retrofit studies is evaluated using the following methods in Fig. 3.2.35. 3.2.4.4.3.4.1.5 Load-bearing capacity of site If in a building, prescriptive methods are not available due to the lack of technical documentation, Table 3.2.26 Knowledge factor categories in foundation analysis.

Performance levels

The structure of soil and foundation and previous Simplified rehabilitation information on the or standard strength of materials Available Not available Special rehabilitation Available Not available

Type the necessary test for soil and foundation LDP & LSP NDP & NLP Minimum Usual Usual Usual Comprehensive

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Seismic Rehabilitation Methods for Existing Buildings

Table 3.2.27 Minimum number of tests according to seismic rehabilitation objective. Usual information level Comprehensive information level

• Removal of two bar samples from the entire foundation structure and two concrete cores. • Drilling a borehole to the penetration depth of loading stress by conducting experiments mentioned in the experiment and digging section of geotechnical studies phase.

Availability of technical documentation during construction • Tests from bar-3 sample and 1
3 core concrete samples • Drilling at least one borehole Unavailability of technical documentation during construction • Tests from sample bar 3
6 and 3 core concrete samples • Drilling at least four boreholes

Figure 3.2.35 Chart of methods for evaluation foundation bearing capacity.

geotechnical studies should be carried out during the rehabilitation process to calculate the ultimate load-bearing capacity of the foundation based on the detailed specifications of the building [1,2]. 3.2.4.4.3.4.1.6 Determining capacity by prescriptive analysis This method is practical if sufficient information and technical documentation are available for evaluation in seismic rehabilitation projects (Table 3.2.28). 3.2.4.4.3.4.1.7 Evaluation stiffness parameters on shallow and deep foundation for modeling First step in calculating foundation stiffness is estimating pri-

mary shear modulus of sub-base soil (G0) for foundation [1,2]. G0 5 •

γvS2 g

(3.2.12)

If test is impractical, it must be calculated considering the valid equations (Table 3.2.29): 1=3 pffiffiffiffiffi 1=3 pffiffiffiffiffi G0 5 20000ðN1 Þ60 σ00 -G0 ðKpaÞ 5 4375ðN1 Þ60 σ00

347

Types of existing buildings: detailed introduction and seismic rehabilitation

Table 3.2.28 Determining complete capacity of the foundation. Shallow foundations Deep foundations

• Prescriptive load-bearing capacity of shallow foundation qc 5 3 3 qallow qallow is the permissible load-bearing capacity listed in the technical documentation available for shallow foundations under gravity loading and based on the results of geotechnical studies In the absence of technical documentation for qallow use below method

• Prescriptive load-bearing capacity of deep foundation Qc 5 3 3 Qallow Qallow is the permissible bearing capacity listed in the technical documentation available for deep foundation under gravity loading

qc 5 1:5QD =A

QD is the building weight and Ais the foundation area

Table 3.2.29 Effective shear modulus ratio (G/G0) [1]. Effective peak acceleration, SXS =2:5 Site class

SXS =2:5 5 0

SXS =2:5 5 0:1

SXS =2:5 5 0:4

A B C D E F

1.00 1.00 1.00 1.00 1.00 0.95 1.00 0.95 0.75 1.00 0.90 0.50 1.00 0.60 0.05 Site-specific geotechnical investigation and dynamic analyses shall be performed

SXS =2:5 $ 0:8

1.00 0.90 0.60 0.10 site response

Second step is investigating the rigidity of foundation structure to foundation soil. This parameter should be evaluated with respect to the type of foundation and by applying the relationships presented in Fig. 3.2.36. If the conditions are right, it is assumed to be rigid, otherwise it will be flexible [1,2]. 3.2.4.4.3.4.1.8 Introducing different types of foundation and foundation modeling Generally speaking, we can use the following three types of

foundation and soil modeling: 1. Separate modeling; 2. Semiseparate modeling; and

348

Seismic Rehabilitation Methods for Existing Buildings

3. Simultaneous complete modeling. This modeling can be done both linear and nonlinear. 3.2.4.4.3.4.1.8.1 Separate modeling The building structure is modeled with rigid supports for columns and walls. After analysis, the reactions of the support are sometimes obtained. These reactions apply to the standalone model of foundation. Stiffness characteristics of components are also considered in the foundation model (Fig. 3.2.37) [2]. 3.2.4.4.3.4.1.8.2 Semiseparate modeling The columns and walls of the building are considered to be flexible. Flexibility is sometimes created by spring modeling. To do this, a spring is positioned at the lowest column node and the lowest wall node modeled as a column, for each degree of freedom (Fig. 3.2.38).

Figure 3.2.36 Chart of evaluation stiffness parameters.

Figure 3.2.37 Separate modeling.

Types of existing buildings: detailed introduction and seismic rehabilitation

349

3.2.4.4.3.4.1.8.3 Simultaneous complete modeling Building structure and foundation members are modeled together in a single model. If the soil is not modeled, at each node of the structure the springs are defined in the same way as separate modeling (Fig. 3.2.39). 3.2.4.4.3.4.1.8.4 Modeling of foundation and soil (Figs. 3.2.40 and 3.2.41) (Tables 3.2.30
3.2.32) 3.2.4.4.3.4.1.8.5 Pile foundation Pile foundation, a kind of deep foundation, is actually a slender column or long cylinder made of materials such as concrete or steel, which are used to support the structure and transfer the load at desired depth by either end bearing or skin friction. Pile foundations are deep foundations. Piles studied in this section are less than 24 in. in diameter [2] (Fig. 3.2.42). 3.2.4.4.3.4.2 Drilled shaft foundation Drilled shafts, also referred to as drilled piers, caissons or bored piles, are deep foundation solutions used to

Figure 3.2.38 Semiseparate modeling.

Figure 3.2.39 Simultaneous complete modeling.

350

Seismic Rehabilitation Methods for Existing Buildings

Figure 3.2.40 Chart for modeling of foundation and soil in shallow type.

Figure 3.2.41 Calculating stiffness of spring.

support structures with large axial and lateral loads by excavating cylindrical shafts into the ground and filling them with concrete. Drilled shaft (caisson) Piles studied in this section are more than 24 in. in diameter [1,2] (Fig. 3.2.43) 3.2.4.4.3.4.2.1 Stiffness parameters In the case of deep foundations, the selfmodeling (cap-piles) can be neglected in the structural model and the entire foundation is replaced by six springs (three transient springs and three rotational springs). The horizontal (lateral) stiffness of the foundation is calculated using the sum of the stiffness of the soil strength adjust the pile, the lateral stiffness of the pile group calculated by the project's geotechnical engineer, or using references in the technical literature. Parameters of stiffness, which are calculated by Winkler model and soilstructure interaction [1,2]. Axial stiffness in deep foundation ðkpv Þ  N  X AE (3.2.13) kpv 5 L n n51

Table 3.2.30 Part one for calculating stiffness of foundation analysis spring.

1:

2:

3:

"   # 0:65 GB L 3:4 B kx;sur 5 1 1:2 22v

0

1 sffiffiffiffi "  0:4 # D hdðB1LÞ @ A β x 5 1 1 0:21 1 1 1:6 BL2 ; βy 5 βx B 2 0 13 "  2=3 # 2 3 1 D B  0:65 dðB1LÞ @2 1 2:6 A5 1 1 0:32 β z 5 41 1 GB 4 L BL 21 B L ky;sur 5 3:4 LB 1 0:4 1 0:85 22v B 2 3   sffiffiffi d4 2d d 20:2 B5 11 β xx 5 1 1 2:5 " #  0:75 B B D L GB kz;sur 5 1:55 LB 1 0:8 "       # 12v 0:6

β yy 5 1 1 1:4

2

4:

5:

0 1 3 GB3 4 @L A kxx;sur 5 1 0:15 0:4 B 12v " #  2:4 GB3 kyy;sur 5 0:47 LB 1 0:034 12v "

6:

kzz;sur 5 GB3 0:53

#

 2:45 L B

1 0:51

d L

20:6

1:9

1:5 1 3:7

d L

d D

0

1

B ; β zz 5 1 1 2:6@1 1 A L

 0:9 d B

352

Seismic Rehabilitation Methods for Existing Buildings

Table 3.2.31 Part two for calculating stiffness of foundation analysis spring. Horizontal spring stiffness Vertical spring stiffness ðuseing six formula to caculate spring stiffnessÞ areaðfoundationÞ 3 areapoint

kend 5

6:83G 12υ

kmid 5

0:73G 12υ

ki 5 li k

Table 3.2.32 Part three for calculating stiffness of foundation analysis spring. Horizontal spring stiffness Vertical spring stiffness ðuseing six formula to caculate spring stiffnessÞ areaðfoundationÞ 3 areapoint

Figure 3.2.42 Pile foundation for the different building.

Figure 3.2.43 Drilled shaft foundation.

ksv 5

1:3G Bð1 2 vÞ

Types of existing buildings: detailed introduction and seismic rehabilitation

Rotational stiffness in deep foundation ðkpr Þ  N  X AE 2 kpr 5 S L n n n51

353

(3.2.14)

3.2.4.4.3.4.2.2 Capacity parameters (strength) The resistance of the piles is

determined using the equations provided for capacity determination, but the following considerations must be considered [1,2]. • The lower bound of the flexural capacity of the pile group is determined by assuming a triangular axial force distribution in the piles and by applying the lower bound of their vertical bearing capacity. For example, if all the piles are the same, the axial force of the longest pile Table 3.2.33 Acceptance criteria of foundation.

System with flexible support System with rigid support In all performance level, the In all performance level except foundation shall be modeled with all immediate occupancy, the vertical load-bearing system foundation shall be model with rigid according to flexibility spring support and without all vertical loadbearing system Linear static and dynamics analysis Linear static and dynamic analysis Acceptance criteria Control of foundation performance with deformation QUD When the ratio of (force/capacity) is κQCE # 3 QUD 5 QG 6 QE acceptable in linear producer Control of foundation performance with force method: In linear producer if we have any sign • In this structure bearing capacity of of deformation, control formula shall foundation is not valuated so for be used and flexibility support the analyzed by linear method, use steel below method: elements. • Using spring or damper • In linear producer QUF force is used • Increase damping for axial load and for analysis. bearing support structure Nonlinear static and dynamic analysis • Then the foundation performance Acceptance criteria control with force • When the ratio of (force/ QUF 5 QG 6 C1 CQ2EC3 J deformation) is acceptable in Nonlinear static and dynamic analysis nonlinear producer method. When analyze foundation with • Forces of QUF for valuation are nonlinear producer the foundation calculated. behavior shall be control with force • In this structure, bearing capacity of QUF # kQCL foundation is not valuation, so for analyzing with nonlinear producer method, use steel elements.

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Seismic Rehabilitation Methods for Existing Buildings

in the tensile side is equal to the lower bound of its vertical tensile bearing capacity and the axial force of the farthest pile in the tensile side is equal to the lower bound of its vertical compressive bearing capacity and the axial force of the other piles. • The upper limit of the flexural capacity of the pile group is obtained by assuming an axial (uniform) distribution of the axial force of the piles by applying the upper limit of their vertical bearing capacity. For example, if all the piles are the same intervals. In this case the axial force of half of the piles on one side of the pile will be equal to the maximum limit of their tensile bearing capacity and the pile strength of the other half of the piles on the opposite side will be equal to the upper limit of their compressive bearing capacity [1,2]. 3.2.4.4.3.4.2.3 Accept criteria Before controlling the bearing capacity, the overturning of the entire structure in the alignments must be controlled using the tensile capacity of the foundations. This is a force-controlled capacity and should not be used expected its boundary. Before valuation the foundation shall be controlled the overturning at the foundation level is very important [1,2] (Table 3.2.33).

3.2.5 Common seismic rehabilitation techniques, details of improving of concrete structures Generally, seismic rehabilitation of concrete buildings is done in two ways [1,2,5,6]:

3.2.5.1 Local seismic rehabilitation of members In locally improving beams, columns, connections, and any other component that is an integral part of the concrete structure is seismically rehabilitated.

3.2.5.2 Completely seismic rehabilitation structure or building Completely structure retrofitting is for cases where seismic rehabilitation is done through general interventions applied to structure on all elements. In this case, the capacity of all components is increased in terms of strength and stiffness. Elements that need localized improvement include

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Figure 3.2.44 Chart of seismic rehabilitation general methods for concrete structure building.

foundations, slabs, beams and columns, and shear walls if available (Fig. 3.2.44) [1,2,5,6]. 3.2.5.2.1 Methods of local strengthening At a glance, the methods mentioned above for local retrofitting of the members are seismic rehabilitation in the form of concrete or steel jackets, the use of fiber reinforced polymer (FRP) fibers or external pretensioning. Of course, there are others to be mentioned hereafter. Seismic rehabilitation techniques of the foundations are geotechnical foundation rehabilitation, structural rehabilitation—increasing the foundation dimensions, solidifying the foundation and reinforcing it to incorporate new shear walls, creating the proper consistency for the foundation to use modern seismic rehabilitation structures. Seismic rehabilitation for reinforced concrete slabs include adding thickness from the bottom or top, adding steel beams, embedding steel strips plates, adding FRP fiber strips. Seismic rehabilitation of concrete beams is reinforcement using steel jacket to improve flexural and shear capacity, reinforcement using concrete jacket, and reinforcement using fibers, reinforcement with external pretensioning for beams. 3.2.5.2.2 Structure retrofitting and rehabilitations strategy The design rehabilitations strategy to improve structural performance and reduce seismic risk to a certain level is acceptable. Rehabilitation strategy includes technical strategy and management strategy. The technical strategy includes five main building blocks: increased lateral stiffness, increased

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Figure 3.2.45 Building behavior when using damper and base isolation for seismic rehabilitation.

lateral strength, increased flexibility capacity, increased energy dissipation in the building, and ground-borne vibration control. Traditional methods may include exterior retrofit of a structural member with ordinary or pretensioned steel, increasing the concrete cross-sectional area by shotcrete, attaching prefabricated parts and pasting steel plates, and so on. Encapsulation of concrete components such as concrete beams and columns using steel profiles and plates is another effective way to increase earthquake strength and reinforce concrete structures. This method of seismic rehabilitation against earthquake has the advantage of not increasing the dimensions of the section, but special measures must be taken to increase the stiffness of the section to control the section. It is also suitable for seismic rehabilitation of concrete structures with very low strength components (Fig. 3.2.45). 3.2.5.2.3 How to use steel jacket? One of the basic ideas and techniques used in seismic rehabilitation of concrete structures was to digging the concrete cover of the structural members and to place additional steel bars in the element and then to cover it with strong glues and resins. This idea, despite improving the capacity of the structure slightly, but cannot still eliminate the problem of steel bars corrosion. Another technique used to seismic rehabilitation concrete structures is the use of steel plates or a steel jacket technique in which steel plates are attached to the surface of the concrete components. But it is problematic in the following ways: • The high weight of steel plates and the difficulties of making these retrofitting components. • Hard access to components and scaffolding needs.

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Figure 3.2.46 Steel jacket the concrete components.

• •

Weakness in adhesion between steel and concrete due to corrosion of steel. Longitudinal restrictions in transferring steel plates to the workshop due to the fact that in seismic rehabilitation projects of concrete structures, beam lengths are generally long (Fig. 3.2.46).

3.2.5.2.4 How to use concrete jackets or reinforced concrete coverings? Using this method increases the stiffness and ductility and overall strength of concrete structures; one of the disadvantages of this method is increasing the dimensions of sections and dead load of concrete structures. The use of this method also requires evacuation of the building and extensive destruction of the concrete structure, which adversely increases the undesirable stiffness of the concrete members (Fig. 3.2.47). 3.2.5.2.5 The retraction or pretensioning method The retraction or pretensioning technique is one of the traditional seismic rehabilitation techniques used to pretensioned concrete reinforced structures. The stretching action immediately increases the load-bearing capacity of the member and reinforces the present structure (Fig. 3.2.48). 3.2.5.2.6 How to install steel or concrete shear wall in concrete existing structures? In seismic rehabilitation method, shear wall attachment to concrete or steel existing structure can change the stiffness of the structure and in addition to increasing the capacity of bearing gravity loads, it also increases the capacity of bearing earthquake lateral loads. In recent years, steel or concrete shear walls have been repeatedly used as a new system for

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Figure 3.2.47 Steel jacking near panel zone.

Figure 3.2.48 Pretensioning method for seismic rehabilitation concrete components.

bearing lateral loads in the design and seismic rehabilitation of structures. The low cost of construction, fast installation, high energy absorption potential, etc. make steel or concrete shear wall a very suitable system for seismic rehabilitation of existing structures. Steel or concrete shear walls can be easily added to existing metal or steel frames (Fig. 3.2.49). 3.2.5.2.7 Using steel braces Adding steel braces to the concrete existing structure will increase the stiffness, reduce the need for flexibility and increase the shear strength of the system, also giving a slight increase in the weight of the structure. The use of divergent brace systems (EBFs) is generally not common in concrete buildings due to their high cost and difficulties in implementing and providing bonding details. But types of convergent bracing systems can be considered in this type of rehabilitation (Fig. 3.2.50).

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Figure 3.2.49 Install shear wall in concrete building.

Figure 3.2.50 Using steel braces for seismic rehabilitation concrete building.

3.2.5.2.8 Using concrete or masonry infill Increasing the strength and stiffness of the system as well as reducing the need for ductility of structural components can be achieved by adding between reinforced concrete panel frames or brick walls, which is one of the most common methods in concrete structures. The added walls can be either new on-site shear walls or shotcrete (Fig. 3.2.51). When constructing structures by this method, it is important to consider whether the existing concrete frame can be part of a composite system. In other words, the load adequacy of existing structural columns should be controlled if they act as members and boundary components of shear walls. In case of insufficient strength of the structural columns, the shear wall can be fully assembled with the boundary members and components separately from the existing concrete frame or reinforced with reinforced concrete wall columns. The second advantage of using the axial compressive load of the existing columns is to reduce the response load caused by the earthquake.

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3.2.5.2.9 Seismic rehabilitation of concrete ceiling using steel plates or section One of the methods of controlling the structural rise and stiffness strength and integrity of concrete floors and ceilings is to use steel plates or section. These plates or section must be securely braced to the ceiling and the area between the ceiling and the retrofitting components should be filled with epoxy based grout or materials to provide adequate seismic performance against earthquake and load transfer (Fig. 3.2.52). 3.2.5.2.10 Seismic rehabilitation of concrete ceiling using steel plates or section for preventing the slab punch In this case, the bonding area of the column to the concrete slab is reinforced by cross sections, so that its jointing area is increased to prevent punching due to the lack of bars in that area (Fig. 3.2.53).

Figure 3.2.51 Using infill for seismic rehabilitation of concrete building.

Figure 3.2.52 Seismic rehabilitation of slab with using new beam.

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3.2.5.2.11 Increasing the shear capacity of the column using cross brace In directly connecting the slabs to the column, shear stress caused by piercing shear is an important stress. If higher shear capacity is required to counter the piercing shear, the following methods are often used (Fig. 3.2.54): • Increase dimension and cross section of the column. • Connecting steel plate gauge to the column by using special diethyl ether and resin. In this method of seismic rehabilitation, using steel straps at the beamto-column connection (maximum shear) at regular installation intervals retracted by tightening the steel clamp will decrease shear capacity. 3.2.5.2.12 Seismic rehabilitation of connections The beam-to-column connections in reinforced concrete moment frames are considered the most critical points, due to the attachment under

Figure 3.2.53 Seismic rehabilitation of slab with increase shear punching area between column and slab.

Figure 3.2.54 Increasing the shear capacity of the column using cross brace.

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Figure 3.2.55 Seismic rehabilitation of connections with steel cover plate.

reciprocating tensions. Therefore improving the performance of the connection node and its seismic rehabilitation will improve the overall system performance and the seismic rehabilitation of the entire building. There are various ways to strengthen the connections as follows, which according to different criteria, one or a combination of them is selected to improve the performance of the connections and strengthening them against earthquake (Fig. 3.2.55): • Injection of epoxy resin in steel jacket concrete connections. • Use X-shaped pretension section. • Seismic rehabilitation and reinforcement of connections using FRP. • Install steel jacket on concrete connection. • Creating steel cage in concrete connection. • Pretensioning connections. • Creating a concrete jacket at the connection. 3.2.5.2.13 Using FRP fibers FRP systems became famous in the 1980s, which is considered to be a compound or composite substance because of its two main components, including fibers and their adhesives. In the composites, the chemical and physical properties of each component alone are reserved. However, together they produce new material with new physical properties and new mechanical behavior that have special applications. In FRP composites, new physical properties including light weight, thinness, corrosion strength, high tensile strength several times as much steel, and the appropriate elasticity coefficient, which is approximately the same as steel have made their applications in seismic rehabilitation and remodeling of concrete, steel, and masonry very widespread (Fig. 3.2.56).

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Figure 3.2.56 Using FRP for seismic rehabilitation.

• • • • • • • • • •

Advantages of FRP polymer composites: low weight; high flexibility; easy to carry and install; no need for corrosion protection systems; cut into custom pieces; high strength to weight ratio; high toughness and strength; and ability to strengthen both internally and externally. Disadvantages of FRP polymer isolators: vulnerability to fire; and unable to use FRP strips on rough surfaces.

3.2.5.2.14 Adding extended moment frames Extended moment frames have high ductility and high energy dissipation if the criteria are met. Due to low stiffness, the response of this system to lateral forces are accompanied with the increasing deformations; this creates problems for nonstructural components and also with the increase in secondary deformation, it even leads to the overall instability of the structure. Due to their low stiffness and softness, these systems can absorb power after the failure of the main resistant systems and prevent structural damage if the main strength system is not responsive. It should be noted that the added frames can also be external (Fig. 3.2.57). 3.2.5.2.15 Using seismic isolators (base isolation) and damper For options of using base isolation and damper, you can use the descriptions provided for retrofitting’s methods in steel buildings (Section 3.3.5.1.1.5.10).

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Figure 3.2.57 Adding extended moment frames.

3.2.5.2.16 Methods of calculation for seismic rehabilitation of shallow foundation The addition of shallow foundation adjacent to the existing shallow foundation can be one of the appropriate seismic rehabilitation methods for shallow foundations. The usual condition is that both existing and new foundations are of a strip nature and are joined together by some elements. In seismic rehabilitation, design considerations and providing details should be considered. 3.2.5.2.17 Effective width of foundation Different methods are used to design foundation. The first way is to assume that the new foundation itself will bear the loads caused by new coverage. Another way is to divide the load between the new foundation and the existing one based on their levels. The most complicated method is to identify possibly different stiffness between existing soil under foundation that is more consolidated and the new one, which is probably flexible due to lighter loads and being newly constructed. Sometimes a jack is used to move loads to the new foundation. • Shear transfer Connecting new and existing foundations using the dowel rebar is a standard method, however one must determine whether or not the dowel bars are needed. The dowel bars embedded in the foundations and the wall above that should be designed so as to be appropriate for transferring the force that is expected to be beard by the existing foundation. • Unreinforced existing foundation Existing foundations might have been made of unreinforced masonry or of concrete with inadequate reinforcements. If the foundation is wide enough to show beam-like behavior under bearing pressure, the

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•

•

•

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embedded inferior dowel bars can be placed in greater depth near the foundation base to act as a positive reinforcement. Design considerations and providing details include followings: New foundation deeper than existing one The main purpose of adding a new foundation is not to overload or empty the soil base. So the best way is to align the depth of new and existing ones, but it is not always possible. In low-adhesion soils, the soil may fall from the existing soil base into the new excavated area, leading to the movement of the foundation. To modify this, substructure is used. Substructure refers to the excavation of a series of short pit that are spaced at sufficient intervals, and then a canal is dug out from the bottom of the first pit to bottom of the existing foundations and filled with new concrete. These steps repeat for every pit. Another method of substructure is intermittent building of long pier foundations under the new foundation to transfer the foundation support in depth so that no new foundation is needed to deepen. New foundation with lower depth than existing ones If drilling is shallow, the new foundation, in case it is loaded, can apply eccentric and disturbing loads to the existing foundation, which is not desirable. Therefore it is common to add more depths to the new foundation and align it with existing one. This additional depth is usually reinforced by a less number of reinforcements. Existing foundation in the same construction direction of new foundation To execute the new foundation, a portion of the existing one must be cut to allow foundation to be reinforced. This can be done by jack hammer or chainsaw. The capacity of the foundation should be controlled under temporary conditions where its dimensions are reduced and it is under eccentric loading. Implementing deep foundation adjacent to existing shallow foundation Implementing a deep foundation in the vicinity of an existing one is done well. Drilling constraints may be very high, including failure to meet access to requirements and height restrictions for equipment, lack of possibility to recess sufficiently to place the rig against an existing wall, vibrations during drilling, and collision with installations along the drilling path. Usually, when the exterior part of the building is accessible, diagonal drilling is performed below the existing foundation. Usually, in-situ concrete foundation intervals are usually selected so that the existing foundation and wall can be easily drilled past or adjacent to the drilled hole. After the pier foundation and wall

366

• •

•

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foundation has been implemented and sewn to the existing wall, a composite system will be created. Although many engineers allocate gravitational loads to the existing paddle foundation and overturning of the column to pier foundation, in fact, live and earthquake loads are distributed on the basis of relative rigidity. Adding deep foundation adjacent to the existing one In some cases, a deep foundation is implemented in the vicinity of the existing one. New deep foundation includes in-situ pier foundation or micropiles. Structural rehabilitation of existing shallow foundation Structural rehabilitation of existing shallow foundation can generally be classified into two major groups: compressive capacity enhancement and tensile capacity enhancement. The compressive strength of the paddle and strip footings can be modified by spreading the foundation bed, replacing the foundation with a longer one; adding micropiles; bracing the foundation using existing insitu pier foundations, adding micropiles to the existing foundation and adding ties to connect separate paddle foundations. Inadequate tensile capacity rehabilitation of paddle and strip footings is performed using methods similar to those used to rehabilitate compressive capacity, which include spreading foundation bed to increase dead load, replacing with a longer foundation, adding micropiles, bracing the foundation or tying it to existing adjacent foundation and adding ties adjacent to the foundations and columns to bear extra dead load and uplifting. Adding micropiles adjacent to existing strip footing The use of micropiles in strip footings for seismic rehabilitation is primarily due to inadequate compressive capacity in the strip footing toe under the wall and inadequate tensile capacity in the strip footing heel under the wall. In this regard, the foundation spreads more and micropiles, also known as bracing piles, are added. If the micropiles are connected by strip footing, the loads are divided between two different members based on their relative rigidity. The strength and stiffness of the micropiles in the geotechnical report should be evaluated by a panel of experts. The assumed strength depends on the soil capacity and structural capacity of the pile, including pipe, grout and reinforcements. In compressive stiffness, the movement of pile members and the surrounding soil should be considered. Micropiles bear uplifting. Structural tensile strength in the micropiles is lower than their compressive strength and is usually only provided by their reinforcement, unless specific details are provided to engage top of the concrete housing for tensile strength. Tensile stiffness is

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•

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also usually low, and tensile flexibility is achieved by elongation of the reinforcement and the surrounding soil motion. Investigation of the effects of corrosion and its seismic rehabilitation methods Generally, micropile jacketing is uncovered. Depending on the amount of soil corrosion, this permanent jacketing corrosion occurs over time. There are methods to evaluate the lost thickness of steel pipe due to corrosion. By using these methods the reduced thickness and reduced lateral and buckling capacities of the pile can be calculated. Due to the small size of the dimensions, generally the larger capacity of the micropiles results from friction. Therefore the geotechnical compressive capacity of the micropile is generally equal to their axial tension capacity. Seismic rehabilitation of paddle foundations Foundations are generally rehabilitated when the compressive and tensile capacity of paddle foundations are insufficient. A paddle foundation can be placed beneath the columns of braced frame, bending frame, or a concrete column under a discontinuous shear wall and be subject to compressive and tensile forces beyond its capacity. Altering the dimensions or replacing existing foundations increases compressive or tensile capacity by increasing dead load. The following should be considered when seismic rehabilitation is being carried out. The existing reinforcement and overlap with slab located on the ground and transfer shears between existing and new foundations. In this regard, the existing slab reinforcement is probably in the form of a net. To minimize vertical displacement, existing and new slabs need to be sewn together. For overlap, the floor slab reinforcement network can be maintained by slab destruction or implement dowel bars on the edge of the existing slab. Also, shear transfer between the foundations is required. This can be done by indenting the existing surface. Some engineers chamfer the surface of existing lateral foundation so that the top is wider than the bottom and therefore the pressure is externally applied to out plane by compression load. Some engineers run the new foundation a little deeper than the existing one and remove the soil at the edge of the existing foundation from below. So the new foundation acts like a corbel to bear the downward pressure of the existing foundation. If the existing foundation is not replaced, shoring will be needed. Proper consolidation of the foundation bed and complete filling of the new concrete beneath the column is necessary to minimize or eliminate any settlement of the foundation caused by the nonuse of piles (Figs. 3.2.58
3.2.60).

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Figure 3.2.58 Seismic rehabilitation of paddle foundations method one.

Figure 3.2.59 Seismic rehabilitation of paddle foundations method one.

Figure 3.2.60 Adding micropiles adjacent to existing strip footing.

3.2.6 Two real case study examples 3.2.6.1 Example of three-story concrete moment frame building with semirigid diaphragm This project, located in one of the cities in Iran, is a four-story building (including basement) which was built in 1995. The structure system in this building is intermediate concrete moment frame and the type of foundation

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Figure 3.2.61 Picture of the project under study.

is the concrete reinforcement strip foundation. To avoid increasing the complexity of the computation volume in this example for earthquake parameters, the Peak Ground Acceleration or PGA is used 0.35g [7] for prescriptive data for this project. The average number of users of the building at the peak time is 500 persons. The total area of the building is 4300m2 , which is built on four floors. This building should maintain its usability in the event of mild to moderate earthquakes and minimize casualties by maintaining its static position in severe earthquakes. Therefore this building falls into the category of public buildings of great importance. The building has an educational purpose and will be reused after rehabilitation. Given the operational considerations, including operational expectations, crisis management needs, and the process of selecting a building for seismic rehabilitation, this building should be considered for a basic seismic rehabilitation objective (LS-BSE1 and CP-BSE2) [1]. In this example, it is attempted to better understand the concepts in the context of a seismic rehabilitation process. In this example, the SI unit is used to describe topics (Fig. 3.2.61). 1. Assessment of existing building vulnerability to provide seismic rehabilitation objective. 2. Investigating seismic rehabilitation practices for existing structures. 3. Providing ultimate seismic rehabilitation method for existing structures. 3.2.6.1.1 Seismic rehabilitation steps for the project • Qualitative evaluation of seismic rehabilitation for the project. • Digging and tests reviews. • Quantitative assessment of building vulnerability. • Offering three seismic rehabilitation options. • Preparation of seismic rehabilitation plans.

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3.2.6.1.1.1 Qualitative vulnerability assessment

In the qualitative evaluation of a building, a set of information is required for quantitative assessment. In this section, the vulnerability is presented numerically in a specific range. 3.2.6.1.1.1.1 Geometric specifications of the building The building with 62.80 m length and 20.20 m width is dimensionally in accordance with field visit and available plans. Other building features in Table 3.2.34. 3.2.6.1.1.1.2 Type of ceiling and structures in existing building According to the information received from the residents, the ceiling for the building structure under study is a concrete block joist. The type of staircase is considered concrete slab. In this case according to the description given in Chapter 1, Understanding the Basic Concepts in Seismic Rehabilitation, for diaphragms, this ceiling is considered parallel to the beams have rigid diaphragm and the concrete slab and perpendicular to beams have semirigid diaphragm (Fig. 3.2.62). Table 3.2.34 Geometric specifications of the existing building. Floor Area (m2) Opening (%) Height (m) Weight of floor (ton)

Basement Ground floor First floor Second floor

1351 1246 1246 496


9.18 9.18


Figure 3.2.62 A critical plan of existing building.

2.80 3.90 3.90 3.35

811 680 680 298

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3.2.6.1.1.1.3 Groundwater level and history of liquefaction In terms of topography, the building is built on flatten ground and the groundwater level is over 10 m. There is also no history of liquefaction in this area. 3.2.6.1.1.1.4 Identifying seismic rehabilitation objective Given that the rehabilitation objective in this building is a BSO rehabilitation objective, the building must be assessed to provide life safety in earthquake having probability of exceedance 10% in 50 years and provide collapse preventions in earthquake having probability of exceedance 2% in 50 years. 3.2.6.1.1.1.5 Specifying knowledge factor The degree of validity of the results of the information collected from the existing building, by the knowledge factor k, applies to the capacity calculation relationships of each component of the structure. Therefore in the above project, the defined factor for this building is considered at the conventional level k 5 1 due to the absence of structural drawings after defining the digging agenda and tests. 3.2.6.1.1.1.6 Adjacent buildings 3.2.6.1.1.1.6.1 The building is free from four sides Examine executive weak-

nesses in structure and nonstructure components and connections. Up to this point of studies (prior to digging) regarding the year of construction and objective observations, no certain decisions can be made on design defects and executive imperfections. However, qualitative evaluation is done: • Based on the visit, no traces of failure, adhesion, cracking, slumping or corrosion were observed. 3.2.6.1.1.1.7 Height to building dimensions’ ratio The ratio of height to dimension in this building is calculated as below, since these ratios are less than 3, so it is not a lean building. ! !     14:85 14:85 H H 5 0:73 and 5 0:23 5 5 D D 20:20 62:80 N -S E -W 3.2.6.1.1.1.8 Symmetry in building plan (in terms of mass and stiffness) In the building, any protrusion and intrusion geometrically are symmetrical. Regarding nearly symmetrical layout of walls on floors and unanimous distribution of mass in plan and height, floors are nearly symmetrical in terms of mass and stiffness.

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3.2.6.1.1.1.9 Protrusion and intrusion in the Plan Based on local observations, no more than standard permissible values of protrusion or intrusion have been observed in the building. 3.2.6.1.1.1.10 The status of the opening surfaces and their proximity to the floor diaphragm Except for the staircase, which is less than 50% of the floor area, the building has a floor of 7:25 3 15:80 ðm2 Þ on the ground floor and the first opening on the north side of the project (on the staircase). 3.2.6.1.1.1.11 Inconsistency of building Regarding the observations of the building project, in case there is a flexural building in any direction of the building which is determined after digging, the building will not have any consistency problems. 3.2.6.1.1.1.12 Gravity and lateral load-bearing system In the building, according to preliminary observations, the gravity bearing system is a concrete moment frame beam and column. It is worth noting that the floor ceiling system is block joist and no interruptions are not observed in load transferring paths. According to the observations and visits, the lateral load-bearing system of the building is also an intermediate concrete moment frame. It is worth noting that definitive comments on the type of lateral load system will be made after the necessary diggings. 3.2.6.1.1.2 Qualitative evaluation of regularity in the plan

1. Due to the almost symmetric geometric shape and symmetrical distribution of the walls, the distance between the center of mass and the center of stiffness seems to be less than 20% of the dimensions of the building in each direction. It is worth noting that definitive comments will be made after analyzing the building. 2. As the floor of the building is a joist block, changes in diaphragm stiffness will not be significant. 3. According to observations, there is no interruption in the path of lateral force transmission. 4. Due to the relative symmetry of the load-bearing members in the building, the floors appear to have less than 20% displacement relative to each other.

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3.2.6.1.1.3 Qualitative evaluation of regularity in height

1. Mass distribution in height must be examined, that is, each floor must have no more than 50% mass difference from the lower floor. On first and ground floors, due to little change in floor ceiling weight, small changes and equality of floors height, this section will be met. 2. The lateral stiffness of any floor shall not be less than 70% of the lateral stiffness of the floor on its own or less than 80% of the average stiffness of the three floors above. According to the observations made, the lateral load-bearing system of the building is a concrete flexural frame which will satisfy this section due to the similar height of the floors. 3. The lateral strength of any floor shall not be less than 80% of the lateral resistance of the floor above. According to the observations made, the lateral load-bearing system of the building is a concrete flexural frame, and therefore, the subject of this section will be satisfied. 3.2.6.1.1.3.1 Condition of interior walls and façade (outer) walls The outer walls of the building are 35 cm thick and the inner walls are 22 cm. The height-to-thickness ratio of the basement walls for the exterior and interior walls are 8 and 12.7, respectively, on the ground and first floors, 11.1 and 17.7, respectively. On the second floor, these values are 9.6 and 15.2, which should be carefully monitored in the quantitative evaluation section. Investigation of the possibility of separation and collapse of nonstructural parts and components, especially facade and glass components, and the possible loss of life and financial damage in the quality assessment of noncore and nonstructural components (Fig. 3.2.63). 1. Failure to restrain shelves and cabinets may threaten the safety of project residents due to shakes caused by earthquakes.

Figure 3.2.63 Library shelves are close to the window without proper restraint.

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Water and gas pipelines are surface, and power lines have been inbuilt in most cases. According to the observations, no corrosion was observed, but it is not possible to comment on the corrosion status of inbuilt components at this stage. 3.2.6.1.1.3.2 Investigate the presence of heavy objects on large openings, cantilever and upper floors No heavy objects were seen on the large openings, cantilever and upper floors of the project. 3.2.6.1.1.3.3 Changes made to the building after initial construction Based on the visits, no changes to the Structural Plan appear to have taken place. However, due to the absence of an initial architectural plan of the building, it is not possible to definitively determine any changes to the Structural Plan. 3.2.6.1.1.3.4 General specifications of site Site Specifications in terms of liquefaction history, high subsidence of the ground and landslide 1. Due to the risk of liquefaction due to the plan of overall liquefaction potential and that the groundwater level in the project site is estimated to be more than 15 m in the initial studies, therefore, the liquefaction potential is low. 2. Due to the lack of geotechnical studies, comments will be made after the required studies. 3. With regard to landslides, as there is not much slope on the project site, there seems to be no danger of landslides in the area. 3.2.6.1.1.3.5 Site specifications in terms of earthquake risk Evaluation of the fault potential requires careful application of the necessary procedures by the relevant experts, but according to the investigations and knowledge about faults in and around the city, no faults has crossed the site of this project. Therefore the risk of a fault is very low unless a new fault is identified in the area or a fault occurs due to an earthquake. Given that the city is in a very high seismic area, the peak ground acceleration or “PGA” is 0.35g [7] for project area. Result of preliminary assessment of the building 1.Design quality 2.Construction quality 3.Material quality 4.Quality of component, joints, and details’ execution

Good Good Good Good

’ ’ ’ ’

Average& Average& Average& Average&

Weak& Weak& Weak& Weak&

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5.Quality of resistant lateral load-bearing system 6.Foundation and site quality 7.Quality of nonstructural components’ execution 8.Conformity of building performance to existing plans 9.Does the building meet the level of life safety performance? 10.Does the building need seismic rehabilitation? 11.Does the building need further examinations?

Good ’ Average& Weak& Good ’ Average& Weak& Good ’ Average& Weak& Good ’ Average& Weak& Yes &

NO&

More evaluation ’

Yes &

NO&

More evaluation ’

Yes ’

NO&

3.2.6.1.1.4 Digging and tests

An introductory list of digging and testing required (geotechnical and materials strength) is provided. Based on the observations made by the building and due to the type of structure and due to the lack of access to the structural plans of the building, taking into account the hypothetical typing, approximately 20% of each foundation type, column, and beams were digging (Fig. 3.2.64). According to the results of the digging, the criteria mentioned in the minimum guidelines have been observed to cover all ambiguities as far as possible. Regarding the tests due to the concrete structure of the building and due to the lack of material strength testing reports, four tests for reinforcement stretching and three concrete core testing in foundation and

Figure 3.2.64 Catheterization plan location and tests.

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Table 3.2.35 How to determine the number of samples Row Type number Number of Percentage of types digging of the of the type required desired type of digging

needed. Percentage or minimum number recommended in the instructions

1 F1 4 1 25% 2 F2 24 4 17% almost 3 F3 16 3 18% almost 4 F4 4 2 50% 5 C1 12 3 25% 6 C2 84 19 22% almost 7 C3 56 13 23% almost 8 C4 16 8 50% Investigation of the number and adequacy of diggings of concrete sections

20% 20% 20% 20% 20% 20% 20% 20% for foundations and fittings

Row Experiment

minimum number of instructions

The number or request by seismic rehabilitation engineer

1

2

4

6

7




4

2 3

Rebar strength Coring concrete Mortar shear capacity

two for beams and columns were requested. In addition, exposing is performed regarding the types so that all assumed types are covered. Finally, to test the potential of walls as infills, four mortar shear strength experiments were requested in the building. The number of digging was considered sufficient due to the symmetry of the structural and similarity of foundation type shown in the tables (Table 3.2.35). 3.2.6.1.1.4.1 Examine the number and adequacy of project building experiments To obtain geotechnical information, at least one borehole at a depth of at least 15 m or depth of penetration of loading stress is required. The layout of diggings and tests should be carefully prepared and made available to relevant groups and experts. An example of the plan as well as the introduction of digging and testing sites is provided for readers. According to the material presented in Chapter 2, Seismic Rehabilitation and Practical Methods in Seismic Rehabilitation of Existing Buildings, as you can see, all sites have been encoded, thus, for more information on how to encode, see materials in Table 3.2.36.

Types of existing buildings: detailed introduction and seismic rehabilitation

Table 3.2.36 Specifications of testing required. Row Component Coding Define Row Component Coding

1 2 3 4 5 6 7 8 9 10

Foundation AZ4/-1/3/1 AZ4/-1/3/2 AZ4/-1/3/3

F,V,C F F,V, Tr AZ4/-1/3/4 F,V AZ4/-1/3/5 F,V,C AZ4/-1/3/6 F,V AZ4/-1/3/7 F,V, Tr AZ4/-1/3/8 F,V,C AZ4/-1/3/9 F AZ4/-1/3/10 F,V

377

Define

11 Connection AZ4/-1/1/11 D,V 12 of beam AZ4/-1/1/12 D 13 to col AZ4/-1/1/13 D,V 14 15 16 17

AZ4/-1/1/14 AZ4/-1/1/15 AZ4/-1/1/16 AZ4/-1/1/17

D D,V D D,V

18 19 20

AZ4/-1/1/18 D,V AZ4/-1/1/19 D,V AZ4/-1/1/20 D

3.2.6.1.1.4.2 Rapid qualification of vulnerability Qualitative evaluation based on numerical parameters according to the structural characteristics provides a quantification of the building vulnerability within a given range. Considering the rapid qualitative assessment of the vulnerability, it appears that the building falls within the average vulnerability range. However, it is advisable to provide a deeper look at the vulnerability of the complete quantitative assessment structure after performing the required tests and catheterization. 3.2.6.1.1.4.3 Determine the building configuration based on digging and tests 3.2.6.1.1.4.3.1 Information on structural and decryption on structural members and connections The examination of the gravity load-bearing system con-

sists of the configuration of the members and its components and joints to identify their characteristics and to determine the connection between the members of the load and the structural system. The information needed to load the building and perform the building vulnerability calculations required in this survey. The gravity load-bearing system in this building consists of concrete beams and columns. The results of the diggings are summarized as follows (Fig. 3.2.65). 1. Ceiling properties: Due to the lack of structural drawing plans, according to the diggings, the ceiling of the building was joist-block type. According to digging the ceilings of the basement, ground floor, and first floor have been implemented with 25 cm height that are in 65 cm distance from each other and blocks of 20 cm height and 50 cm

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Seismic Rehabilitation Methods for Existing Buildings

Figure 3.2.65 Digging of components.

Figure 3.2.66 Structural plan of existing plan.

width. Different layers of ceiling of floors include flooring, joist-block ceiling, and finish-coat plaster. In Fig. 3.2.66, executing details of floors ceilings are illustrated. As it is seen, the total thickness of the floors ceilings is 40 cm consisting of 2.5-cm tile, 8-cm cement-sand mortar, 5-cm concrete on joist, 20-cm block, and 2.5-cm fine work (including 2.5-cm stucco plaster). In addition, total thickness of upper floor ceiling is 50 cm consisting of 1.5-cm Bituminous waterproofing, 2.5-cm asphalt, 6-cm cement-sand mortar, 5-cm sand, 10-cm Pumice, 5-cm concrete, 20-cm block, and 1.5-cm stucco plaster. 2. Concrete beams properties: Beam framing plan in this building consists of one type of concrete beam shown by B1. Beam type B1 is made of 35 3 55 ðcm2 Þ section. Longitudinal bars of this beam in two span heads are deformed rebar’s 8 φ 24 that are placed in two upper and lower rows (i.e., upper bars bed is made of three bars, lower bed is

Types of existing buildings: detailed introduction and seismic rehabilitation

3.

4.

5.

6.

379

made of three bars, and the middle section includes deformed rebar’s 2 φ 24). Also, closed stirrup of this beam is φ 20@20 cm (i.e., deformed rebar’s 20 mm in each 20 cm). Concrete columns properties: According to diggings, it was revealed that the building has four types of concrete column. The section dimensions for type one and two is 45 3 45ðcm2 Þ and section dimension for third type is 40 3 40ðcm2 Þ. Type 4 columns are steel columns holding sunshade in south wing of the building, made of two IPE140. The location of these columns is shown in columns plan with details related to concrete columns. It must be stated that longitudinal reinforcements of mentioned columns are made of deformed rebar’s number 24 and closed stirrup of that deformed rebar’s is size 10 which are place in 30 cm distances and 15 cm at each end (Fig. 3.2.67). The seismic performance of the infill frames in this building was not considered due to the cuts in these infill frames on basement floor and the large area of openings. Infills of the building are the elements that play a role in stiffness and strength. However, regarding the high length of the opening in these infill frames, hollowness, and low connection of these members to main elements of the structure (beams and columns), they have little effect on seismic function of the building. Geometry and location of the foundation: Concerning the geometry and location of the foundations based on the diggings carried out it can be said that there are two types of foundations. Type F2 5 100 3 500(cm) is two individual foundations of the entrance and the rest of the area is F1 5 60 3 50(cm) (Fig. 3.2.68) Examining lateral load-bearing system and its components: the lateral load-bearing system of the project is a flexural frame system that is

Figure 3.2.67 Example of column tip of structure.

380

Seismic Rehabilitation Methods for Existing Buildings

laterally supported by concrete beams and beams in the building. Therefore the lateral load-bearing system of the building is intermediate concrete moment frame of the building which transfers the lateral forces to foundations levels. 3.2.6.1.1.4.4 Determining minimum and maximum material strength regarding the test results In accordance with the testing and digging agenda, the building was tested and finally the resulting numbers for minimum and maximum strength were extracted using the FEMA 356 (Table 3.2.37). 3.2.6.1.1.4.5 Conclusion from the specification by service and test consultant In this section, the specifications required for material evaluation are provided by laboratory service consulting engineers and are presented in the following Table 3.2.38. This information will then be used to quantify vulnerabilities. 3.2.6.1.1.4.6 Soil and foundation To determine the site specification, mechanical boring with a depth of approximately 15 m and a hand drilling hole with a depth of 5.5 m were dug. Summary of results from hole for qualitative assessment is presented in Table 3.2.39.

Figure 3.2.68 Foundation plan of existing building. Table 3.2.37 Conclusion from the specification by service and test consultant. Objective Description Test result (kg/cm2)

Compressive strength of concrete

Coring on foundation Coring on beams and columns Determining steel Foundation Beam and column yield limit

0

Fc 5 254

0

Fc 5 116

Fc 5 185 Fc 5 125

0

0

Fc 5 283

0

Fc 5 198 Fc 5 100

Fy 5 4482 Fy 5 3162 Fy 5 3620 Fy 5 3504

0

0

381

Types of existing buildings: detailed introduction and seismic rehabilitation

3.2.6.1.1.5 Descriptive evaluation of buildings needs for rehabilitation

In this project, computer modeling as a three-dimensional model was used to evaluate the building needs for rehabilitation. The purpose of the project evaluation is to reanalyze the structure in accordance with FEMA 356 guidelines, which will provide a suitable lateral system seismic rehabilitation if needed. 3.2.6.1.1.6 Selecting analysis model

Two-dimensional models can be used to analyze some soft or completely rigid diaphragm structures. A block joist system has been used on the ceiling of the building. Therefore the use of two-dimensional models is also permitted, but a three-dimensional model has been used to ensure that the actual behavior of the model is similar to the actual structure. 3.2.6.1.1.7 Defining gravity load (dead and live load)

In quantifying the vulnerability of a building to calculate and estimate indices such as mean gravity stress, base shear, and collapse, we need to determine the gravity loads of the building. In this regard, loading of dead and live loads must be done carefully. Table 3.2.40 presents the dead and live loads in this project. Table 3.2.38 Material strength properties. Member Expected strength

Concrete in foundation Concrete in beam and column Rebar’s in foundation Rebar’s in foundation

0

Lower
bounded strength 0

Fc 5 240 0 Fc 5 146 0 Fc 5 3822 0 Fc 5 3562

Fc 5 190 0 Fc 5 101 0 Fc 5 2888 0 Fc 5 3480

Table 3.2.39 Soil and foundation properties. Foundation Properties

Stripes Squared

B (m) Qa (kg/cm2) B (m) Qa (kg/cm2)

1 2.55 1 1.71

2 1.92 2 1.03

3 1.28 3 0.88

Table 3.2.40 Defining gravity load (dead and live load) for existing building. Row Name Value (kg/m2) Row Name Value (kg/m2)

1 2 3

Class 350 Corridors 500 Roof (snow load) 150

1 2 3

Structure ceiling 750 Façade outer wall 558 Inner walls 580

382

Seismic Rehabilitation Methods for Existing Buildings

3.2.6.1.1.8 Determining the main structural and nonstructural components in the model and their stiffness

All existing beams and columns are considered to be the main structural members in the modeling of the building. The effect of these infill frames on the lateral strength of the building is also ignored due to the hollowness and lack of connection between the frames in this building (Fig. 3.2.69). 3.2.6.1.1.9 Foundation modeling

In most cases, the foundations of the model can be neglected at the beginning of modeling and analysis, assuming vertical load-bearing lateral systems based on rigid bedding. However, such assumptions are not permissible for buildings subject to seismic or rehabilitation performance for immediate occupancy and since the expected level of performance is favorable, modeling and analysis of associated foundations is neglected and the foundation is modeled separately. 3.2.6.1.1.10 Basic controls of building structures

According to the geometrical dimensions and coordinates of the location of the center of mass and the center of stiffness of the building, the distance between the center of mass and the center of stiffness in each building is not more than 20% later than as presented in Table 3.2.41.

Figure 3.2.69 Three-dimensional computer simulation using software. Table 3.2.41 Calculating the center of mass and center of stiffness of the building. Story Diaphragm XCM YCM XCR YCR

Story Story Story Story

1 2 3 4

D1 D2 D3 D4

31.325 31.325 31.325 31.325

9.75 9.549 9.687 10.267

31.325 31.325 31.325 31.325

9.75 9.75 9.75 9.75

Types of existing buildings: detailed introduction and seismic rehabilitation

Table 3.2.42 Percentage of mass change in building floors. Story Diaphragm Mass X

Story 1 Story 2 Story 3

D1 D2 D3


0.92 0.79

383

Mass Y


0.92 0.79

In this building, the mass distribution at the height of the building is almost uniform, so that the mass of any floor, with the exception of the roof and truss roof, has not changed by more than 50% relative to the floor mass below (Table 3.2.42). 3.2.6.1.1.11 Nonlinear vulnerability assessment: determining target displacement for push over the structures

The required parameter of the structure is the target displacement as the most important parameter of the nonlinear analysis of the structure calculated in this section for the existing building. The periodicity considered is derived from computer modeling in linear behavior analysis. T 5 1:4S C0x 5 0:79 ; Ti 5 0:529S ; eX g-C1 5 1:0 T C0x 5 0:78 ey 5 1:57S

Sax 5 0:6517 ðTe2 Þ -δt 5 C0 C1 C2 C3 Sa T $ 0:1-C2 5 1:1 C3 5 1:0 gð4π2 Þ Say 5 0:5488

δ 5 28 cm δt - tx δty 5 29:5 cm To achieve this displacement, up to 1.5 times this value is applied to the computer model. The required foundation meter for the strip foundations of the existing building under study where the geotechnical studies have been carried out and the results provided are: qallow 5 1:71 kg=cm2 -qc 5 3 3 2qallow 5 3 3 2 3 1:71 5 10:26 kg=cm2 3.2.6.1.1.12 Combined gravity and lateral loading

The first step is to combine the gravity and lateral loading, the upper limit and the lower gravity load QG effects, which must be calculated from the following equations: QG 5 1:1ðQD 1 QL 1 QS Þ QG 5 0:9:QD

384

Seismic Rehabilitation Methods for Existing Buildings

Step two: Gravity load efforts should be combined with earthquake load efforts. This should be done by taking the reciprocal effect once with a positive sign and again with a negative sign. Design efforts are made in earthquake (QE) and therefore members whose behavior is deformation controlled are calculated by combining the following effects (QUD 5 QG 6 QE ), and design efforts on members whose behavior is force controlled are calculated by combining the following effects QUF 5 QG 6 C1 CQ2EC3 J . 3.2.6.1.1.13 Control of nonlinear structural analysis results

Given that the structure under consideration is the bending frame of concrete. To investigate its nonlinear behavior, M3 hinges at both ends of beams and PMM hinges at two ends of concrete columns were used. The specifications of the hinges were defined in computer modeling according to the details of the element reinforcement and based on the values specified in FEMA 365 tables. A sample of plastic hinges defined for the columns is shown in Fig. 3.2.70. According to the instructions, at least two types of lateral load distribution must be applied to the structure. Regarding the main period of the structure, the lateral load distribution pattern of the first type, that is, proportional to the lateral forces resulting from the analysis of the oscillation modes of structural failure, should be used. The second type of lateral load is a uniform distribution in which the lateral load is proportional to the weight of each floor defined horizontally in two orthogonal directions x and y in the model. The effect of both types of lateral load distribution is at the center of mass of the floors.

Figure 3.2.70 Hinge properties of beam and col sample.

Types of existing buildings: detailed introduction and seismic rehabilitation

385

3.2.6.1.1.14 Evaluation of nonlinear structure response

It should be noted that in the analysis, some columns have exceeded the collapse limit, and these results indicate that the target building in the target relocation does not satisfy the desired performance level and is vulnerable (Fig. 3.2.71). 3.2.6.1.1.15 Foundation evaluation and analysis

Since behavior of the soil under the foundation is deformation controlled and the foundation behavior is force controlled, the k value is taken into account according to the information level and the desired performance level. The results of foundation loading with linear static analysis loading pattern and the combination of the corresponding loads in the desired building foundation are shown in Fig. 3.2.72. Because the lower

Figure 3.2.71 Forming plastic hinges at the point of operation for the first type distribution along the 1 y.

Figure 3.2.72 Rebar’s needed in direction x.

386

Seismic Rehabilitation Methods for Existing Buildings

boundary of the concrete compressive strength of the foundation of the project is 185 kg=cm2 the foundation rebar of the project was also provided for the relevant loads in the images. 3.2.6.1.1.16 Evaluation of underlying soil compatibility with acceptance criteria for load bearing

Design efforts in members whose behavior is deformation controlled are calculated by combining the following effects: The behavior of soil is deformation controlled; therefore the pressure under the soil is controlled by a combination of abovementioned loads. Since there is a high number of load combinations, a sample has shown that in all cases, the pressure under the soil is less than the load-bearing capacity of soil. Thus it can be concluded that it is not vulnerable. 3.2.6.1.1.17 Preparation of primary methods of seismic rehabilitation (review of strategies)

3.2.6.1.1.17.1 Improvement of structural components with poor performance against earthquake force By examining the vulnerability of the building, it was found that many of the columns in the basement and first floor and parts of the foundations are vulnerable to side loads. Since this building does not have sufficient strength to withstand seismic loads, it therefore has general weaknesses and needs to be reinforced or a lateral load-bearing system installed. 3.2.6.1.1.18 Fixing or reducing irregularities in the existing building

According to the building vulnerability studies, it was found that the building is almost regular in plan and height. However, as mentioned in the previous section, to deal with lateral forces, the building needs to be fitted with a new lateral load-bearing system or reinforced concrete structure. To meet the standards of a regular construction, new elements or reinforcement of the existing concrete structure must be arranged in such a way as not to cause irregularities in the building. 3.2.6.1.1.19 Determining the lateral stiffness required for the building

As mentioned in the building vulnerability assessment, the lateral stiffness of the building is only supported by a concrete flexural frame in both directions. The following methods can be used to provide the required stiffness in this building: 1. Increase the stiffness of the building by incorporating shear walls, adjacent columns.

Types of existing buildings: detailed introduction and seismic rehabilitation

387

2. Increase the stiffness of the building by incorporating shear walls without border elements. 3. Increase the stiffness of the system by reinforcing the existing concrete framework. 3.2.6.1.1.20 Increase the stiffness of the building by incorporating shear walls and reinforcing adjacent columns

To build such a system in the building, frames need not be architecturally significant. According to the architectural plan of the buildings on the different floors, it was found that the number of frames in which placing shear walls does not change the architecture plan of the building is not high. Depending on the building plan and the different parts of the building, there are a limited number of infill frames available in all floors. In these openings, the walls are reinforced with concrete cover and attached to the walls with the necessary reinforcement. According to preliminary calculations, there will be a need to strengthen the foundation for the construction of shear walls. It is worth noting that in this design only frames where shear walls will be installed and foundations are reinforced will require demolition and temporary closure to reinforce the building. In short, it can be argued that the design for shear walls in this option is the best option for this building with shorter running time, easier execution, less demolition and closure, and low costs (Fig. 3.2.73). 3.2.6.1.1.21 Increasing strength by adding shear walls and covering columns adjacent to walls

As the lateral resistance in this building is low due to the weakness of the proper lateral load-bearing system, it is possible to increase the strength by adding shear walls in suitable locations that cause less architectural problems and to rehabilitate the building. Among the benefits of this method

Figure 3.2.73 Location of new concrete shear walls for seismic rehabilitation method one.

388

Seismic Rehabilitation Methods for Existing Buildings

are less demolition that is limited only to the shear wall openings. Other advantages include less run time and easier implementation for the local workforce. In this method, there is need to reinforce foundations at the location of shear walls to face efforts made in walls. Overall, this option can be further explored as the best option for rehabilitation of the building (Table 3.2.43). 3.2.6.1.1.22 Increasing the stiffness of the building by incorporating shear walls without boundary elements

To build such a system, as in the previous option, there is a need for openings that do not have a lot of architectural problems to build walls. According to the architectural plan of the buildings in different floors, it was found that the number of openings, in which having a shear wall does not alter the architecture of the building, is not large, but this option requires larger shear walls due to the lower strength of the shear walls. Therefore shear walls are mounted on exponential walls around the building and do not pose an architectural problem (Fig. 3.2.74). Increasing the strength in this way, given that the lateral strength in this building is low due to the weakness of the lateral load-bearing system, has an approach similar to that of a boundary element wall in building architecture. Only in the nonboundary element method, due to the lower strength of the walls do we need to build more walls (Table 3.2.44). 3.2.6.1.1.23 Increasing the stiffness of the system by reinforcing the existing concrete framework

In this method, reinforcing the building is done through reinforcing beams and columns with new reinforcement and increasing their dimensions with new concrete cover. For this purpose, lateral load-bearing system is reinforcement only by special axial flexural frames, but regarding the vulnerability of most columns on the first and second floors, all columns, must be reinforced. The rehabilitation volume in this option will be more in comparison to the shear wall (Fig. 3.2.75). It is also possible to reinforce the concrete frame with the concrete cover of the columns. In this method, the column strength and the reinforcement of the longitudinal and transverse reinforcement of the structure are sufficiently improved. However, in this method, the volume of rehabilitation required is wide due to the extensive vulnerability of the columns and the foundations of the structure must be strengthened according to the calculations (Table 3.2.45).

Table 3.2.43 Seismic rehabilitation with adding shear walls with bo-elements.

Wall

Story

Section

Longitudinal bar’s

Wall-1

1

L:725; t:30 cm

20@20Ф

Wall-2

1

L:720; t:30 cm

20@20Ф

Wall-1

2

L:725; t:30 cm

20@20Ф

Wall-2

2

L:720; t:30 cm

20@20Ф

Wall-1

3

L:725; t:30 cm

20@20Ф

Wall-2

3

L:720; t:30 cm

20@20Ф

390

Seismic Rehabilitation Methods for Existing Buildings

Figure 3.2.74 Location of new concrete shear walls for seismic rehabilitation method two.

3.2.6.1.1.24 Comparison of foundation rehabilitation for upper methods

One of the most controversial and most difficult parts of reinforcing an existing building against auxiliary forces are the reinforcement of the base and how the forces are transferred to the ground. There are strip foundations in the building that will require reinforcement and rehabilitation depending on the building's need for new elements or reinforcement of existing ones. As can be seen from the computer modeling results, the amount of foundation reinforcement in the rehabilitation option for strengthening frames is very costly because it requires more reinforcement than other seismic rehabilitation options, so this process can also be evaluated. The layout of the concrete shear wall is a better option for the seismic rehabilitation of this building.

Table 3.2.44 Seismic rehabilitation with adding shear walls without bo-elements.

Wall

Story

Section

Longitudinal rebar’s

Wall-1

1

L:725; t:30 cm

20@20Ф

Wall-2

1

L:450; t:30 cm

20@20Ф

Wall-1

2

L:725; t:30 cm

20@20Ф

Wall-2

2

L:450; t:30 cm

20@20Ф

Wall-1

3

L:725; t:30 cm

20@20Ф

Wall-2

3

L:450; t:30 cm

20@20Ф

392

Seismic Rehabilitation Methods for Existing Buildings

Figure 3.2.75 Seismic rehabilitation with retrofitting column and beam, method three.

3.2.6.1.1.25 Nonlinear analysis for final seismic rehabilitation method

The required parameter of the structure is the relocation of the target as the most important parameter of the nonlinear analysis of the structure calculated in this section for the existing building. To achieve this relocation, the computer model is pushed up to 1.5 times this value. The fundamental period considered is the derivation of computer modeling in linear behavior analysis. T 5 0:73S C0x 5 1:3 ; Ti 5 0:37S ; eX g-C1 5 1:0 Tey 5 0:83S C0x 5 1:3

T $ 0:1-C2 5 1:1 C3 5 1:0

ðTe2 Þ Sax 5 0:892 -δt 5 C0 C1 C2 C3 Sa g-δt Say 5 0:832 ð4π2 Þ

δtx 5 15:4 cm δty 5 18:6 cm

M3 hinges at both ends of beams, PMM hinges at both ends, and middle of columns and concrete shear walls were used to investigate the nonlinear behavior of the structures. Hinge specifications were defined according to the details of the reinforcement elements of the elements and according to the values specified in the structural rehabilitation guidelines tables in chapter 3 in the software. The sample of plastic hinges defined for the columns is shown in Fig. 3.2.76. It should be noted that the beams and columns are eligible for transverse reinforcement and the axial force to capacity ratio in the beams is zero and in the columns greater than 40%. Considering that proper stirrup of the boundary element is made in walls and the axial force level must not be less than 10%, shear walls with boundary elements with low axial force are used in these walls.

Table 3.2.45 Seismic rehabilitation with retrofitting column and beam, method three.

Components

Story

Section

Longitudinal rebar’s

Column AXE 1-4

1 2 3

65 cm 3 65 cm 65 cm 3 65 cm 65 cm 3 65 cm

24Ф8 24Ф8 24Ф8

Column AXE 2-3

1 2

75 cm 3 75 cm 75 cm 3 75 cm

24Ф8 24Ф8

3

75 cm 3 75 cm

24Ф8

394

Seismic Rehabilitation Methods for Existing Buildings

Figure 3.2.76 Nonlinear analysis result.

Figure 3.2.77 PX1p:1:1ðDL 1 LLÞ 1 EQX .

3.2.6.1.1.26 Binary force linear behavior model—structural displacement

To find binary linear behavior of the structure, the structure must be displaced nearly 1.5 times the target displacement in each main direction and different types of loading (appropriate distribution with first mode of vibration in target direction and uniform distribution in which appropriate lateral force is calculated relative to weight of each floor). Therefore we must have primary estimations about target displacement. Further, calculations for the building and behavior curves are explained (Fig. 3.2.77). 3.2.6.1.1.27 Foundation rehabilitation

Concerning the acceptance criteria for building foundation according to the abovementioned and considering that the behavior of the soil under the foundation is deformation controlled and the foundation is force controlled, the results of foundation loading with the loading pattern of nonlinear static analyzes and the combination of the corresponding loads in the desired foundation are shown in Fig. 3.2.78. Due to the addition of new concrete shear walls, it is observed that the stiffness of the structure is significantly increased and in this respect the

395

Types of existing buildings: detailed introduction and seismic rehabilitation

effective period of the structure is also significantly reduced. In proportion to the reduction in the fundamental period, the effective displacement of the target is also reduced, in other words, the structure becomes stiff and rigid. Therefore at the time of applying lateral earthquake force, the building shows a suitable performance and has fewer displacements. In addition, the results show that plastic hinges reveal that members in area of life safety to immediate occupancy under earthquake risk level 1 have a suitable performance. 3.2.6.1.1.28 Comparing options economically, technically, and practically

Based on the analysis carried out on the building and with regard to the technical and economic evaluation of the project, review of the implementation conditions, architectural constraints and duration of implementation of each of the proposed options for the implementation of the building rehabilitation plan, the implementations options are generally reviewed economically, technically, and practically. As mentioned in Table 3.2.46, three options for adding shear walls with boundary elements, shear walls without boundary elements, and reinforcing concrete frames were proposed and explored to strengthen the

Figure 3.2.78 Foundation seismic rehabilitation result. Table 3.2.46 Relative comparison of the proposed options economically, technically, and practically. Condition

Implementation Function Implementation Implementation cost difficulty time

Average Shear walls with bo-elements High Shear wall without bo-element Improving High frame

Effect on architecture

High

Average

Average

Average

High

Average

Average

High

High

High

Average

Low

396

Seismic Rehabilitation Methods for Existing Buildings

building. The results show increased stiffness and strength of the building by the addition of reinforcing and hardening elements. The layout of these elements is intended to accommodate even the architectural considerations of the building. The sections required to provide the required strength of the building are designed, and the dimensions and foundation of the building are also controlled for incoming loads. Based on the amount of reinforcement required, the costs and duration of implementation of each of the proposed projects have been estimated. The conditions for all three options are relatively similar, but the cost and duration of implementation with respect to demolition and reinforcement in the foundation as well as the lateral load-bearing system implementation in the second and third options are more than the option of adding a shear wall with a border element. In short, it can be stated that the presented design for reinforcing building is evaluated as a better option with adding shear walls with boundary elements regarding appropriate layout, reliability due to increase in building system, shorter implementation time, less demolition, and less costs. 3.2.6.1.1.29 Relative comparison of costs

As mentioned in Chapter 2, Seismic Rehabilitation and Practical Methods in Seismic Rehabilitation of Existing Buildings, by the end of seismic project, calculations must be based on the rehabilitation method. According to calculations, the ratio of the offered option costs for rehabilitation to reconstruction cost is extracted in percentage. In the study building, regarding that the ratio of costs of seismic rehabilitation to reconstruction cost is 8.59%, therefore it can be concluded that rehabilitation design is economic. Comparing time and cost of Implementing Rehabilitation (Fig. 3.2.79 and Table 3.2.47)

3.2.6.2 Example of a tall 22-story concrete moment frame building with rigid diaphragm and central concrete core 3.2.6.2.1 Introduction of practical example (buildings with concrete structure) The example given for reinforced concrete buildings belongs to a real executed project, consisting of a high-rise building with 17-story and an area of approximately 30,000 m2. The project is located in Tehran, Iran. The building was designed about 15 years ago in accordance with the bylaws of that time. The structure was built for 5 years, and then the project construction was halted for 10 years. In terms of the instrumentation

Types of existing buildings: detailed introduction and seismic rehabilitation

397

Figure 3.2.79 An overview of the seismic rehabilitation of the existing building for example 01.

398

Seismic Rehabilitation Methods for Existing Buildings

Table 3.2.47 Relative comparison of costs for seismic rehabilitation. Offered Seismic rehabilitation Ration of reconstruction costs option time and seismic rehabilitation costs

Option 1

Four months

8.59%

Figure 3.2.80 Existing condition of the building before new floors and new facade changes.

of this building, it has a partially restrained concrete moment frame with concrete core. About this building, in accordance with the new Iranian urban development criteria, engineers have decided to consider increasing the area of the building to approximately 35,000 m2 in the form of an increase in the number of floors to 22 floors and major changes in the building's appearance. The purpose of this example is to introduce the reader to the high-rise buildings that have undergone major changes in architectural designs and changes in the number of floors and facades during the implementation period. It was about how to start the project, what concepts to look at, and how to finish the project. In this example, the SI unit is used to describe topics (Fig. 3.2.80). In this regard, seismic rehabilitation engineers have been looking for solutions to provide objective, to make sure of the existing situation due to regulation changes and to ensure the new situation created after future changes. The axioms of this example have led to seismic rehabilitation studies centered on three main axes: • Seismic vulnerability assessment of the existing situation. • Examine the need or need for a seismic rehabilitation project after the expected architectural modifications.

Types of existing buildings: detailed introduction and seismic rehabilitation

399

•

Presentation of improvement plan to provide rehabilitation target based on changes made and final status presented in this example. In Part I, Seismic Vulnerability Assessment and Existing Situation, as mentioned in the previous sections of this book, this section consists of three main stages, the first stage being a qualitative evaluation based on an inspection. The second step is to prepare and complete the information required for the digging and testing instructions, and the third stage involves quantitative evaluation of the vulnerability for the status quo and the expected end-case status. In Part II, as the architecture of the building is undergoing many changes, such as increasing the number of floors, incorporating new facades to design the new facade and new architecture of residential apartments, we have tried to provide appropriate decision-making perspectives for the new structural system as well as provide options for assessing whether or not seismic rehabilitation is required. In Part III, the seismic rehabilitation method and final approach used in this building are analyzed and presented. As mentioned in Chapter 2, Seismic Rehabilitation and Practical Methods in Seismic Rehabilitation of Existing Buildings, the seismic rehabilitation method in this building is complete intervention. Damage analyses: In the studied building, the increase in the building area has 30% changed relative to the primary area. This leads to thoughts about what effect the number of floors has on mass, stiffness, and eventually in seismic capacity of the building. For this purpose, the engineer needs enough experiences and deep understanding in facing the probable problems and damages (Fig. 3.2.81). Questions that might arise for seismic rehabilitation engineer include: • Does this building in its current state have the potential to be used in a potential earthquake based on new regulations? • What solution is proposed to increase the area to reach the expected infrastructure of the user? • Would the seismic system be responsive if some floors were added to the building? • How will the existing building relate to the new floors and the elements of the building facade? 3.2.6.2.2 Qualitative Assessment of this example As mentioned earlier, the qualitative assessment studies of seismic rehabilitation are generally to collect information on the current state and identify weaknesses and strengths of the building. For this purpose, the required

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Seismic Rehabilitation Methods for Existing Buildings

Figure 3.2.81 A view of the final concept of building which is modeled virtually.

information is provided in brief. In this building, this stage is mostly related to tests due to the impossibility of using the building. 3.2.6.2.3 Process of seismic rehabilitation studies The first step is to evaluate structures whose current status is structural skeleton executed without fishing material, and the aim is to analyze and examine their components. The primary purpose of rehabilitation in these buildings is to upgrade the design system based on old regulations to new ones. In this regard, the building must first be evaluated and analyzed linearly and after identifying the vulnerable elements, the elements should be evaluated in a nonlinear domain so that the nonlinear capacity of the elements can be used to achieve the expected performance level. Therefore in the project, the existing structure is first modeled in accordance with FEMA 356 and iranian code No.360, and then the structure is fully evaluated in linear terms. In a broad view, similar to as-built maps, careful consideration is given to modeling the beams to extract the resulting stress from the as-built elements. Structural studies and seismic rehabilitation of existing buildings are carried out by two expert teams. The first team performs the seismic rehabilitation of the existing structures, and the second team conducts the additional structural design operations required to increase the number of floors and the building area. Given that the focus is on seismic rehabilitation studies and practices, the design calculations of the new adjoining structure are avoided and only the results needed for seismic rehabilitation are used (Fig. 3.2.82).

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401

3.2.6.2.4 Part I of seismic rehabilitation studies: history of building and future operation The history of the design and construction of the building dates back to 15 years. Its first use was residential, and now it also will be residential. Based on experience in reducing mass and preventing excessive changes, the decision is made to demolish some existing floors and build new floors with materials lighter than concrete building. In this regard, part of the weight to increase the area of the building is compensated by the demolition of some floors. Thus three floors of the upper concrete structure will be demolished, and seven new floors of steel structure will be constructed. 3.2.6.2.5 General characteristics of floors The building existing at the beginning of the seismic rehabilitation operation prior to any architectural or structural changes has specifications as shown in Fig. 3.2.83. The extra area is intended so that the floor area of

Figure 3.2.82 An overview of the status of the building at the time of study.

Figure 3.2.83 View of the current status architectural plan.

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Seismic Rehabilitation Methods for Existing Buildings

each floor is approximately 20% of the original floor area due to the addition of new balconies and the attachment of the steel structure to the old concrete structure. According to the three-dimensional plan presented, it is determined that the building layout has the same type of floors and the changes are mainly due to the facade and dimensions of the balconies. 3.2.6.2.6 Existing building architecture specifications According to field inspections by the local expert team, total status of project architecture is presented in Table 3.2.48 in qualitative evaluation and future use section (Fig. 3.2.84). 3.2.6.2.7 Existing building structure specifications The required basics about structural system specifications are presented in Table 3.2.49. As mentioned before, considering the existing clues, ductility of the structural system is assumed average. There is no neighboring building around this building; therefore the structure plan has no constriction joint. Openings are placed in core and stairways are built in this area. Building specifications of the existing part are extracted according to inspections and field examination and presented in Table 3.2.49. Structural as-built plans are available. Therefore target structural changes are applied to available plans in qualitative evaluation section. Finally, structural plans are used in modeling. 3.2.6.2.8 Examining visible defects of the building After initial inspection of the project and examining structural elements, no fundamental defects such as serious cracks on structural elements or Table 3.2.48 Existing building geometrical properties (area properties). The situation before the seismic The situation after the seismic rehabilitation rehabilitation Row Title

Explanations Row Title

Explanations

1 2

Residential 17

1 2

Residential 22

30,000 m2 Irregular

3 4

70 m

5

3 4 5

Usage Number of building floors Area Dimensions of building Building height up to foundation

Usage Number of building floors Area Dimensions of building Building height up to foundation

35,000 m2 Irregular 90 m

403

Types of existing buildings: detailed introduction and seismic rehabilitation

Figure 3.2.84 Architect plan of existing building. Table 3.2.49 Existing building geometrical properties (height properties). Row Story number Structure type Roof type Height ðmÞ

1 2 3 4 5

Parking 1
4 Lobby Half the ground floor One to twelve Roof garden

Concrete moment frame 1 Concrete center core

Block joist and slab Block joist and slab Block joist and slab

3.4 3.4 3.55

Block joist and slab Block joist and slab

3.5 3.5

inappropriate appearance were observed in concrete parts. Additionally, there were no damages such as creep, yielding, cracks, recession, corrosion, and execution weaknesses in structural parts. Furthermore, cantilevers and columns surrounding the structure were examined in terms of

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Seismic Rehabilitation Methods for Existing Buildings

adding steel cantilevers for providing a new level of structure, and suitable situations for digging and coring for agenda were identified. 3.2.6.2.9 Determining the figure of the building According to initial inspections, building columns are circular concrete section type in surrounding area and internal rectangular areas. Building beams are concrete rectangular type. Walls shape like shaft on every floor are connected to each other and roof by using connectivity beams. 3.2.6.2.10 Introducing seismic rehabilitation objective for the building The rehabilitation objective for this project was basic rehabilitation which is to increase the area of the project which is accordingly applied to different parts of this example. Regarding the selected rehabilitation target, providing safety performance level in level one earthquake risk is considered. 3.2.6.2.11 Determining material specification The material specifications for in this project are determined through the available technical documents and destructive and nondestructive tests on members including walls, columns, beams, and foundations. 3.2.6.2.12 Status of technical documents As mentioned in Chapter 2, Seismic Rehabilitation and Practical Methods in Seismic Rehabilitation of Existing Buildings, to determine awareness factor of available technical documents is of high importance at the beginning of seismic rehabilitation project. This parameter has a significant effect on the number of tests and digging and how they are carried out. In this building, the technical documents are available to examine the used reinforcement and concrete in beams, columns, ceiling, and foundation. Fortunately, regarding the visibility of main structural components, we can identify dimensions and types of components through field inspections. For example, dimensions of columns, beams, type of ceiling, stairways, and foundation in terms of neighboring buildings are visible. 3.2.6.2.13 Determining concrete material specifications Considering criteria and regulations in Journal FEMA 356 about concrete material, in case the change coefficient results of all cores is less than 25%, compressive strength of concrete must be determined. In case this factor is more than 25%, the number of extracted cores in this project from any type of component must be increased by a given amount, and the results

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Types of existing buildings: detailed introduction and seismic rehabilitation

of compressive strength of cores resulting from any type of components must be used to determine the compressive strength of any structural component. Some results of destructive and nondestructive test are used in calculations (Table 3.2.50). 3.2.6.2.14 Determining steel material specifications Considering the criteria and regulations in Journal FEMA 356, the expected specifications of steel material at common knowledge level are equal to the specifications of the nearest steel level which has strength less than the obtained values from tests. In case the minimum specification of steel materials are required, we can divide expected values by 1.1. According to evaluations, GOST 578-82 is equivalent to A3 for bars (Table 3.2.51). Table 3.2.50 Results of concrete strength test results (kg/ cm2). Position Schmitt Ultrasonic Core Position Schmitt Ultrasonic Core

Beam C1 Col C2 Beam C2 Col C3 Beam C3 Beam C4 Slab C5

392 350 350 385
301

Slab C6

406


Good Good Good Good
Fair/ medium


Col C7

385

Good

Col C8

322

Good

243 Col C9 261 Slab C10 Wall C11 175 Wall C12 Wall C13 343 Beam C14 295 Wall C15

421 336 287 315 308 280 436

Good Good Good Good Good Good Good

2283 312 117 190 388 306 405

312 Foundation C15 292 Foundation C16 303 Foundation C17







351







398







382

Table 3.2.51 Test results for bar tensile. No Specimen Diameter Cross Yield force name (mm) section and stress (cm2) (N/mm2)

Ultimate force and stress (N/mm2)

Elongation in length (%)

1 2 3 4

671 798 628 795

16 15 13 16

16-1 18-1 22-1 22-2

15.77 17.95 22.16 22.03

1.95 2.52 3.85 3.8

520 489 487 454

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Seismic Rehabilitation Methods for Existing Buildings

3.2.6.2.15 Determining basic level for basic shear of applying earthquake level To apply earthquake force on structure, determining basic level is necessary. Therefore we can use rigidity of beams or a collection of ceiling beams and slabs to increase ceiling rigidity. In this project, regarding that the first three floors are surrounded by guardian walls attached to the structure, we can consider the third floor as the basic level, that is, 0.10 m from ground level. 3.2.6.2.16 Is it possible to use the building in the current status according to seismic rehabilitation regulations? As mentioned earlier, it has been 15 years since designing the building in the current status. This structure must be first analyzed by using performance evaluation according to Journal FEMA 356, and the results must be examined. For this purpose, coefficient of applying earthquake force must be calculated based on a parameter of structure weight. Regarding the structure specification and time period, according to the formula in Chapter 2, Seismic Rehabilitation and Practical Methods in Seismic Rehabilitation of Existing Buildings, values for evaluating earthquake force are calculated as explained in Table 3.2.52. According to the materials mentioned in Chapter 2, Seismic Rehabilitation and Practical Methods in Seismic Rehabilitation of Existing Buildings, time period of the structure is calculated. Regarding that this building is of the structures with integrated concrete wall frames, therefore, the following formulas are used for calculations. Thus in structural calculations 360 codec, the value of experimental time period can be increased up to 1.4. However, this value Table 3.2.52 Calculating sustainability index in direction Y. Story hi δi Vi Pi

θi

Story Story Story Story Story Story Story Story Story Story Story

0.12 0.15 0.17 0.16 0.17 0.15 0.15 0.15 0.14 0.12 0.11

15 14 13 12 11 10 9 8 7 6 5

4.55 4.2 4.2 3.5 3.5 3.5 3.5 3.5 3.5 3.5 3.5

0.09363 0.093343 0.100776 0.087988 0.092793 0.095229 0.094641 0.088835 0.083285 0.082066 0.080025

2431 3323 4083 4917 5646 6279 6830 7338 7772 8139 8435

3178.761 4593.055 5984.377 7713.971 9428.694 11,119.84 12,815.53 14,625.07 16,454.47 18,345.11 20,237.3

Types of existing buildings: detailed introduction and seismic rehabilitation

407

must not be higher than the analyzed time period. It must be mentioned that the structure weight is modeled automatically by adding parameters to the computer. The building weight (W) extracted from computer model is 29,700 ton. T 5 0:05ðHÞ3=4 -T 5 0:05 3 ð49Þ0:75 5 0:92S V 5 C1 C2 C3 Cm Sa W -V 5 0:5085W 0:5 2 ð0:92 3 1:4Þ -C1 5 1:5; C2 5 1:0; C3 5 1:0; 2ð0:5Þ 2 2 Cm 5 1:0; Sa 5 0:339; K 5 1:395

C1 5 1 1

Compound loading according to FEMA 356 is as follows: COMBOðn1Þ 5 1:1ðQD 1 QL 1 Qs Þ 6 QE and COMBOðn2Þ 5 0:9ðQD Þ 6 QE

3.2.6.2.17 Examining the effects of P
Δ According to paragraph 3.2.5.1.1 in FEMA 356, the effects of this parameter on basic index parameter was calculated according the following equation, and eventually, by considering that the value of this parameter was much smaller than 0.33, therefore it was not applied in seismic rehabilitation decision-making. For example, the effects of this parameter on upper floors are presented.   Pi δi θi 5 Vi hi As presented in Table 3.2.52, regarding the small value of this parameter, we can exclude it from determining rehabilitation design. However, by considering the calculations for the fourth floor and above, this parameter must be taken into account in displacement increase for each floor. In computer modeling, this process can be done automatically by the software. 3.2.6.2.18 Results of analyzing and evaluating the computer modeling After analysis and examination, structure failure modes were identified. Mass contribution percentage in both directions was 99.5, which shows

408

Seismic Rehabilitation Methods for Existing Buildings

correct modeling. Also, time period in the first mode was equal to 1.74 s with contribution percentage 78. In this project, beams and columns are deformation controlled and shear walls are force controlled. Therefore in the stage for vulnerability assessment, value of m coefficient was extracted for deformation-controlled elements according to materials presented in the related chapter and tables. The awareness factor in this project was also considered equal to 1 considering the level of information. After computer modeling, it was found out that (1) the main performance of structure time period was calculated according to average concrete flexural frame, and (2) the building in its primary status is suitable in terms of seismic system and mass-stiffness ratio. Therefore by maintaining the same structural weight and increasing stiffness ratio in the whole structure, it is possible to increase substructure. DCR in beams and columns is mainly smaller than 1, and DCR in shear walls is near 1. 3.2.6.2.19 What solution is recommended to increase the number of floors in this building since a large area is needed? To increase the number of floors, the weight of structure must have the least number of changes. For this purpose, the following process must be considered. 3.2.6.2.20 Examining the structure weight 3.2.6.2.20.1 Balancing the structure mass beside increasing the number of floors

One of the important parameters in seismic evaluation of buildings, especially tall buildings, is evaluation of mass. At the first glance, we face a building which consists of a heavy structure made of concrete materials and has a higher weight than other buildings. In this case, the first concern of an engineer is to find the right approach to increase the number of floors with the least changes in weight. For this purpose, the mass of the structure is first examined and the structure weight is estimated. This stage seems the best solution to place two floors on concrete building with truss, which by considering the materials, will be approximately 952 ton (Fig. 3.2.85). 3.2.6.2.21 Key recommendation Regarding that in a typical six-story building with steel structure and lateral load-bearing flexural frame system plus its concrete core, beams and columns have 100 kg/cm2 in each square meter, it is therefore

409

Types of existing buildings: detailed introduction and seismic rehabilitation

Figure 3.2.85 Demolition of the last two concrete floors. Table 3.2.53 Destructive part specification. Row Story number Structure Roof type type

Story area

Story height

1 2

1504 379

3.5 3.5

Eleven and Twelve Roof garden

CMF CMF

Block joist and slab Block joist and slab

recommended that the number of floors is increased by designing steel structure and placing this structure on upper floors. Then, this structure must be analyzed in terms of vulnerability by considering the attached structure. Regarding the subject of this book on seismic rehabilitation, the calculations for this steel structure is not presented and only key points and results are presented and examined. 3.2.6.2.22 Destructive part specification In this building, there are three old structures that are demolished. It must be noted that demolition is done in a way that no damages are caused to the floors beneath (Table 3.2.53). 3.2.6.2.23 Specifications for the attached structure The specifications for seven steel structure used to increase the area of this building are presented in Table 3.2.54. All sections from core to the last building, even for the attached steel structure, are considered (Fig. 3.2.86). 3.2.6.2.24 In case these floors are added to the building, is there a need to strengthen the seismic system and installing a secondary system? By understanding the possibility to add this number of floors to the building, the most critical question here is whether or not the building is

410

Seismic Rehabilitation Methods for Existing Buildings

responsive or not. Further, the situation will be evaluated after the increase in the number of floors so that by identifying the damages, an appropriate seismic rehabilitation solution is selected accordingly. The process is in the following. The first step is accurately design the upper steel structure (Fig. 3.2.87). In this case, the following must be considered for homogenizing in this project: • Determining the lateral seismic system for the new upper floors Considering that lateral stiffness by the floors below is ten times higher than the average stiffness of the new upper floor structure, hybrid steel Table 3.2.54 Specifications for the attached structure. Row Story number Structure type Roof type

1 2

Eleven to seven SSMF Roof garden SSMF

Story area Story height

Steel metal deck 1530 Steel metal deck 379

4.2 4

Figure 3.2.86 Computer simulation of existing building and adjoining structures.

Figure 3.2.87 Computer simulation of existing building and adjoining structures.

Types of existing buildings: detailed introduction and seismic rehabilitation

411

Figure 3.2.88 Computer simulation of the connection of the new structure to the existing central concrete core.

•

flexural frame with concrete reinforced shear walls can be used in the design for the lateral load-bearing system. Determining ceiling system and walls Structure ceiling in all parts, except for parts inside shear wall core (areas of corridors to reaching the internal walls) can be in form of steel deck and concrete slabs can be used in the mentioned parts. Walls are the light brick type (Fig. 3.2.88).

3.2.6.2.25 Steel structure part of the project 3.2.6.2.25.1 Determining geometric specifications of used sections

In this project, columns are in box shape and beams are mainly I shape. In internal part of shear wall core, concrete columns are used. On the first floor of the new structure in which columns are executed compositely, a part of composite cross-section column with specifications of ST52 steel is used. Console beams around are made around nonprismatic section and by using steel ST37. In Fig. 3.2.89, the type of these sections is illustrated. 3.2.6.2.25.2 Nonprismatic section beam for cantilever

Regarding the results of calculations, the upper part weighs around 583 ton which is much less than the estimated weight, 952 ton. Therefore the mass ratio is completely observed mathematically.

412

Seismic Rehabilitation Methods for Existing Buildings

Figure 3.2.89 View of cantilever beams for new balconies.

3.2.6.2.25.3 Designing parts of the attached façade

It must be stated that after average calculations of upper steel structure, steel parts of balconies of façade are also designed according to the new architecture. In addition, relating steel parts to concrete parts has been explained before. In this example, these explanations are provided at the final part of the example. • The second Step in Seismic Rehabilitation of the Project Attaching the designed steel structure on the existing one and computer modeling can be done in two ways 1. Simplified modeling In the simplified modeling, we can extract the base force including column ends and beam connections to shear walls from the steel structure modeling. Then we can apply this information to another computer model in given parts, and finally, analyze the structure based on this information. This type of modeling is mostly used for preventing faults and problems of inconsistency in steel and concrete structures. 2. Comprehensive modeling In this modeling, the output results of sections are added to the available computer model and the structure is modeled with steel and concrete structures. The second method is used in this example (Fig. 3.2.90). • The third step in seismic rehabilitation of the project, qualitative vulnerability assessment after adding upper steel floors without strengthening in linear analysis method The aim here is to examine vulnerability and intervention level after adding the new structural floors on the existing building. For this purpose, the structure of this building is analyzed according to Journal FEMA 356 and results are examined. Calculation of applying earthquake force

Types of existing buildings: detailed introduction and seismic rehabilitation

413

Figure 3.2.90 Implementation of steel adjoining structure and assembly on old building.

parameter after attaching the new concrete steel structure on the old concrete structure was done in computer modeling and by taking into account the calculated weight of the building (W) in the computer modeling which was nearly 2913 ton. 3

T 5 0:05ðHÞ4 -T 5 0:05 3 ð70Þ0:75 5 1:21S V 5 C1 C2 C3 Cm Sa W -V 5 0:387W ; K 5 0:5T 1 0:75-K 5 1:597; 0:5 2 ð1:4 3 1:21Þ -C1 5 1:5; C2 5 1:0; C3 5 1:0; 2ð0:5Þ 2 2 Cm 5 1:0; Sa 5 0:258

C1 5 1 1

3.2.6.2.26 Analyzing output results from computer modeling As it is seen, the increase in height leads to softness of the structure and decrease in stiffness. Therefore we need to analyze and examine the structure floor by floor so that we can evaluate defects locally. Further, descriptive vulnerability analysis of a floor is presented (Fig. 3.2.91). 3.2.6.2.27 Analyzing the effect of component stiffness on the structure stiffness To analyze this effect, the structure system is divided into two separate systems, and finally, by analyzing the effect of removing shear wall stiffness on structure, the building is comprehensively analyzed. Concrete shear wall system in this situation must tolerate 70% of shear force, and the flexural frame structure must bear 30% of the shear force resulting from an earthquake. Figures and obtained results from the software for analyzing

414

Seismic Rehabilitation Methods for Existing Buildings

Figure 3.2.91 Stress display in beams after evaluation.

and evaluating in separation mode of primary and secondary system of concrete and steel parts show that columns are vulnerable. Vulnerability of columns in these conditions is due to this fact that increasing the number of floors leads to vibration period in the structure. Consequently, by maintaining relative mass, structure stiffness is decreased and the structure functions more softly. Regarding that concrete shear walls play an important role in depreciation of earthquake forces, this structure has less reflection mode and much force is transferred to columns, causing columns that were not vulnerable previously to be vulnerable. 3.2.6.2.28 Sample analysis of vulnerability on the first floor As an example, all the elements of the first floor are generally interpreted in order to better understand the concepts of vulnerability and expected performance so that a better optimization proposal can be proposed .This interpretation includes the examination of beams, columns, Diaphragm, shear walls, and the initial proposed seismic rehabilitation plan, which is available in the attached table (Table 3.2.55). 3.2.6.2.29 Analyzing average PMM stress of columns on floors For a deep understanding of the overall condition of the structure. In this section, the average stress for each floor is briefly extracted from the modeling and finally presented in the (Table 3.2.56). 3.2.6.2.30 Explaining results from seismic separation analysis on hybrid system Columns on all floors in linear behavior analysis are mainly vulnerable. This shows the necessity of using average concrete flexural frame and shear wall

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Types of existing buildings: detailed introduction and seismic rehabilitation

Table 3.2.55 Evaluation the effect of component stiffness on the structure stiffness on the first floor. Row Analysis Description

1

Beams

2

Columns

3

Diaphragm

4

Shear wall

5

Recommended method for seismic rehabilitation

Beams on vulnerable floor and the cause of vulnerability is asymmetric deformation in beam connections to the core. Sixteen columns were vulnerable in which DCR is between 1.004 and 1.375. According to analysis, regarding that the type of ceiling diaphragm does not function completely rigid, deformations in beams and core lead to partial vulnerability in some beams. Shear wall which must be responsible for 70% earthquake force applied to the floor is not enough for rehabilitation target. Attaching shear wall in two directions, executing micropile for strengthening connection of new wall to foundation and reexamining the ceiling for rehabilitation, strengthening beam collector and chords, and improving columns with FRP fibers.

Table 3.2.56 Floor DCR calculated from column DCR.

Story PMM ratio Story PMM ratio

ST 01 1.308 ST 09 1.30

ST 02 1.301 ST 10 1.33

ST 03 1.31 ST 11 1.33

ST 04 1.19 ST 12 1.47

ST 05 1.26 ST 13 1.45

ST 06 1.33 ST 14 1.73

ST 07 1.39 ST 15 1.83

ST 08 1.37

in an integrated way. On middle floors, chords and collectors are vulnerable mainly in areas surrounding the core. By examining stresses, we can conclude that the only possible and low-cost solution for seismic rehabilitation of the structure is to attach secondary shear wall. Beams that are placed around concrete core are mainly vulnerable. This shows that these beams have problems in terms of geometric dimensions. This happens in cases where chords and collectors are not strengthened in critical areas. Regarding that the ceiling system in this part needs modifications, the seismic rehabilitation method is presented in the final part after examinations of stiffness effects. Columns common in the new facade and balconies are also vulnerable due to application of concentrated force in balconies. This reveals the need for appropriate seismic rehabilitation at panel zone (Fig. 3.2.92).

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Seismic Rehabilitation Methods for Existing Buildings

Figure 3.2.92 Investigation of structural displacement in both cases without and with new shear wall.

3.2.6.2.31 Steps to seismic rehabilitation in this project 1. Placing new shear walls in two directions leads to significant decrease in structural deformations in a way that structure stiffness is nearly doubled. The reason is floor displacement is decreased by nearly 50%. This causes that some vulnerable elements reach the expected capacity. 2. Ceiling system must be strengthened for transferring load to floors’ shear walls regarding that beam around the core is mainly vulnerable. In the place of transferring load from diaphragm to shear walls, regarding that the structure has a ceiling with semirigid diaphragm, it is recommended that the common area of diaphragm and shear walls are made rigid using an appropriate method. As it is seen in Fig. 3.2.93, the area around the core consists of stairway and elevator openings, and the block joist ceiling is surrounded in the triangle area made of three concrete beams. The axial concentrated stiffness of the shear wall is a great number in comparison to contributing beams. The probable displacement resulted at the time of earthquake for shear walls leads to damages to elements such as upper cement blocks and slabs that were sensitive to deformation. In this section, to prevent probable changes at the time of earthquake, the prevention from triangular boundary area common between wall and diaphragm and the related system is analyzed in terms of vulnerability. As it is seen, shear and bending stiffness in shear wall in comparison to basic shear force applied to a floor at boundary area causes relatively low displacement. Therefore regarding the low stiffness of horizontal frame, the diaphragm in the target area causes

Types of existing buildings: detailed introduction and seismic rehabilitation

417

Figure 3.2.93 A lobby floor plan.

damages in ceiling elements at the time of earthquake comparing to shear wall stiffness. 3.2.6.2.32 Diaphragm stiffness considering the 5 cm slab on cement block and joist 3EI

KWall 5

L 3 ð1 1 0:6ð1 1 μÞ KDiafraghm 5

D2 L2

5 5; 421; 345

3EI L 3 ð1 1 0:6ð1 1 μÞ

D2 L2

5 22; 549

These numbers show that in boundary area, there are more deformations in triangular area applied regarding the concentrated force. To prevent this deformation, the target area is rehabilitated in the form of concrete slab and the stiffness is controlled. Stiffness of the diaphragm is seismically rehabilitated considering 30 cm slab. KDiafraghm 5

3EI 2 5 1; 170; 352 L 3 ð1 1 0:6ð1 1 μÞ DL2

Regarding that shear walls are designed for 100% earthquake force, therefore, by regarding the increase in flexural and shear capacity, probable secondary cracks in the direction of earthquake force is prevented. Considering the increased flexural and shear stiffness in triangular area and probable deformations resulting from displacements which are equal to

418

Seismic Rehabilitation Methods for Existing Buildings

1.3 cm and which reach to 0.02 cm in the boundary area, the function is maintained here. Rehabilitation by the method above causes the followings: 1. Increase in lateral stiffness of floors and creating consistency by adding new shear walls and rehabilitation of diaphragm in the common ground. 2. Decrease in displacement of floors by adding new shear walls. 3. Decrease in tensile force in columns by adding new shear walls. 4. Decrease in the effective mass of the structure. 5. Increase in lateral load-bearing capacity. 6. Decrease in stress of the components, which causes that the stress in vulnerable components, reaches to nearly 1 or 1.1. In this case the FRP method for rehabilitation can be applied on the floors. 3.2.6.2.33 Final analysis of the structure through nonlinear method by adding new shear walls According to the regulations in Journal FEMA 356, nonlinear static analysis for evaluating structure of this project was used. Deformations and internal forces resulting from nonlinear static analysis must be examined by using acceptance criteria in Journal FEMA 356. Regarding modeling and nonlinear analysis of the structure, the following rules must be observed: • Selecting control point, loading pattern, determining the main time period, and the analysis method must be according to the related criteria and regulations. • The relation between basic shear and displacement of control point must be recorded for each increase in lateral forces until reaching the displacement at least 1.5 times to the target displacement. • In modeling, gravity load of components combined with lateral loads must be applied according to target load combinations mentioned in the journal. Lateral loads must be applied to the structure in both negative and positive directions and the most critical effects must be recorded for analysis. • In analytical model, force-deformation response in the length of each member is determinable for identifying nonlinear effort. • In this situation, the building is under nonlinear loading according to the discussions mentioned in Chapter 2, Seismic Rehabilitation and Practical Methods in Seismic Rehabilitation of Existing Buildings.

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Types of existing buildings: detailed introduction and seismic rehabilitation

PUSH PUSH

1 5 1:1ðQD 1 QL Þ 2 5 0:9ðQD Þ

As it was mentioned in previous chapters, nonlinear static analysis can be done in two complete and simple forms. In this section, regarding that in this analysis the effect of infill frame is neglected in lateral stiffness, the analysis is in the simple form. 3.2.6.2.34 Modeling materials, elements, and components Structural elements which are effective on lateral stiffness or force distribution or elements which are affected by lateral displacement of the structure are divided into two main and noncore groups. Main elements are the ones needed for tolerating lateral load to reach target performance level. The elements that are not needed to tolerating lateral load can be considered as noncore elements. 3.2.6.2.34.1 Element material specifications

As mentioned before, regarding the test results on material strength, and according to Journal FEMA 356, each element must be considered based on the type of coring results. For example, Table 3.2.57 presents concrete material specifications modeled in computer for available walls. 3.2.6.2.34.2 Effective stiffness of elements

Effective stiffness of all members must be determined with regard to their material specifications, dimensions, amount of reinforcement, and current status of the member in terms of stress level and corrosion. To obtain an appropriate distribution of lateral forces in buildings with load-bearing walls, all walls can be assumed with or without cracks. In this building, shear walls and wall parts can be assumed as cracked. 3.2.6.2.34.3 Plastic joints of the elements

In this project, regarding the performance behavior of the elements, the defining parameters of force-deformation parameters of these members (parameters a, b, and c), and acceptance criteria of parameters are extracted from the tables in Journal FEMA 356 and related chapters (Fig. 3.2.94). Table 3.2.57 Mechanical properties of concrete used in the project. Weight per unit Module of Poisson’s Shear module volume (kg/m3) elasticity (kg/cm2) ratio (kg/cm2)

2500

2 3 105

0.15

113,650

f 0C (kg/ cm2)

273

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Seismic Rehabilitation Methods for Existing Buildings

Figure 3.2.94 An example of the detailed definition of plastic joints for beams in computer modeling.

3.2.6.2.34.4 Target displacement calculation for rehabilitated structures

Target relocation, which is considered to correspond to the displacement of the roof of the structure, reflects the maximum displacement the structure experiences under an earthquake at a specified hazard level. According to Journal FEMA 356, the coefficients method is used to determine the target displacement, which is calculated according to the criteria of the journal, using the following equation: δt 5 C0 C1 C2 C3 Sa

Te2 g 4π2

Since determination of C1 and C2 coefficients requires initial analysis of the structure and determination of the diagram of the structure and its linearization. Then the structure is initially covered by 1.5% of its height (according to ASCE 41/06) and after two linearization of the resulting force-displacement diagram, the magnitude of the target displacement in the desired direction is calculated and is the basis of subsequent analyzes. The details of the target displacement calculations are given below. Initially, Te values are calculated for each of the two main directions of the structure (Table 3.2.58).     Tex :1:694s Te DTi Tey :1:694s Ke DKi

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Table 3.2.58 Parameters calculated to determine target displacement. C0 C1 C2 C3

Sa

1.5

0.327

1

1

1

Figure 3.2.95 Final positioning of existing and new shear walls.

δ 5 1:5 3 0:327 3

1:6942 3 980:6 5 35:5 cm 4π2

Therefore both sides of the structure will be covered up to 35.5 cm. In addition, since the assessment has been considered at the risk level 1, the results have been presented. As shown in the calculations, the embedded shear wall is targeted at increasing hardness, as well as reducing the target displacement by 50%. In this regard, considering that the basis of nonlinear static analysis of force is the shift target displacement on one hand and the stiffness and resistance on the other, it can be concluded that this will improve the performance of all members. The design of new concrete elements such as shear walls and concrete beams is carried out in accordance with the relevant bylaws (Fig. 3.2.95). 3.2.6.2.35 Interpretation of the result of evaluating nonlinear static analysis After incorporation of the new concrete shear wall into the structure, extraction of alternation period and target displacement, it was observed

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Figure 3.2.96 Hinge status of columns under load combination PushG1-X 1 0.3Y. Table 3.2.59 An example of the calculation to capacity ratio of columns under PUSH 01 on the story four.   Story Column Load combo Col section P (axial P= fc 3 Ag Ieff =Ig force) (kg)

Story Story Story Story Story

04 04 04 04 04

C66 C67 C68 C69 C70

Push Push Push Push Push

G1 G1 G1 G1 G1

Max Max Max Max Max

C80-24T26 C80-24T26 C80-24T28 C80-24T28 C80-24T28

739,472.5 655,850.8 723,977.2 835,298.7 823,403.5

0.54 0.48 0.53 0.43 0.42

0.7 0.6 0.7 0.6 0.6

that the columns that had been generally vulnerable in the previous stages were rehabilitated and increased due to the incorporation of the new shear wall and its stiffness and strength, therefore, they are not vulnerable anymore (Fig. 3.2.96). The beams are also vulnerable in the core panels of the shear wall attached to the core. This vulnerability can be removed by rehabilitation in the form of a new slab, and the proposed rehabilitation of the other beams is in the form of FPR fibers (Tables 3.2.59 and 3.2.60). 3.2.6.2.36 How will the existing building relate to the new floors and new elements of the building facade? As the upper floors changed the structure from concrete to steel, there was a need for a reliable transitional floor (Fig. 3.2.97). The joint performance of the concrete and steel columns in the transfer floor had to be ensured that due to the calculated dimensions of the steel column, it could not be properly buried in the concrete column. It was decided to make a part of the column with a stronger material in the shape of a crucifix and to fit the column in a proper manner. Fig. 3.2.98 shows the connection characteristics of the metal and concrete columns.

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Table 3.2.60 An example of the calculation to capacity ratio of columns under PUSH 02 on the story three.   Story Column Load combo Col section P (Axial P= fc 3 Ag Ieff =Ig force)kg

Story 03 C66 Story 03 C67 Story 03 C68

Push G2 Max C80-24T26 538,711 0.39 Push G2 Max C80-24T26 475,070.1 0.35 Push G2 Max C80-24T28 518,753 0.38

0.7 0.6 0.7

Figure 3.2.97 Details of steel structure connection on old concrete structure.

Figure 3.2.98 Connecting steel structure with concrete structure.

3.2.6.2.37 Calculating the connection profile of the crucifix and concrete column In accordance with the provisions of Section 10 of the National Building Regulations of Iran (Design of Steel Structures), the crucifix column and related joints are designed for the following forces: Pu 5 421 ton Mu 5 45 tonUm Vu 5 22 ton

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Comparison of axial column capacity    Ag Fy cross $ 421; 000- 332ð3600Þ 5 1; 195; 200 kgf $ 421; 000-OK Comparison of bending capacity of columns    ZFy cross $ 4; 500; 000- 2440ð3600Þ 5 8; 784; 000 kgUcm $  4; 500; 000 kgUcm -ok

3.2.6.2.38 Calculating the number of shear-head components needed Shear strength of shear stud type shear-head components in accordance with ASCE 07-10 with respect to minimum shear stud height to diameter ratio in columns and beams: φv Qnv 5 Fu Asa ; φv 5 0:65 The shear strength and the number of required shear stud with 1 cm diameter and 5 cm height are obtained from the following equation:     φv Qnv 5 0:65ð4500Þ π 12 =4 5 2297:3 kgf -n 5

Pu 421 5 B183 2:3 φv Qnv

Considering the number of 200 shear stud, we can distribute the shear stud in 25 rows of 8, similar to the one shown in Fig. 3.2.98. Obviously, at the top of the cruciform column alignment until the composite column runs, the minimum number of shear stud should be used for the joint performance of the steel and concrete columns. It is recommended that the same shear stud be applied at twice the number above the level of the crucifix to the floor level. 3.2.6.2.39 Controlling the transfer of steel column shear to concrete bottom column (15th and 16th floors) The steel column attachment to the concrete column must have the capacity to transfer the upper column shear to the lower concrete column. For this purpose, a maximum shear of floor columns equal to 22 ton should be able to be moved to the bottom column by this connection. Regardless of the contribution of the composite column concrete as well as the reinforcement in shear transfer, shear capacity of 28 bolts (sufficient penetration depth is implemented) is 33.25 ton.

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3.2.6.2.40 Designing steel cantilever for new concept changes Designing how to connect these cantilevers to the existing design was done using computer modeling. Then, using the concepts of strength of materials, a manual design was presented to determine the dimensions and initial characteristics of the sheath and its connection. The following is an outline of the proposed scheme for this connection. After numerous computational and executable investigations, this connection was presented as a beam connection using the hardener and side plate shown in Fig. 3.2.99. Fig. 3.2.99 shows the details of connecting these cantilever to concrete columns by steel sheath. The exact characteristics of these sheaths were determined by computer modeling (Fig. 3.2.100). As it can be seen, the sheaths are made of cut metal pipes, and at the two ends are embedded elements that connect two semicircular plates with high-strength screws. In this regard, cement grout was used to create

Figure 3.2.99 Details of connecting new balcony beams to existing columns.

Figure 3.2.100 An example of computer modeling results for shear stress in sheaths.

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Figure 3.2.101 Manufacturing components to connect the steel section to the concrete in the mentioned building.

Figure 3.2.102 Implementation of facade cantilever with the new architecture.

the bonding between the metal and the concrete on the concrete surface (Fig. 3.2.101). Fig. 3.2.102 shows the areas for adding new balconies by sheaths by connecting the steel console beam to the concrete column and executing the steel deck roof. 3.2.6.2.41 Investigation of metal jacket design for vulnerable columns Complex columns are more ductile than concrete or steel columns, and their fittings are similar to steel metal structures. Concrete filling in the column not only increases the load-bearing capacity of the cross section but also increases the strength of the column against fire. In terms of ductility and rotational capacity, however, the hollow filled with concrete

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427

Figure 3.2.103 Investigation of functional behavior of solid and hollow concrete columns.

performs better than other types of mixed columns. Concrete is surrounded by steel, and even when it reaches its final strength, the concrete does not break completely (Fig. 3.2.103). 3.2.6.2.42 Comparison of two behaviors of mixed columns The presence of steel at the outermost cross sections (where there is the most traction) effectively increases the maximum flexural strength of the cross sections. Also, the presence of high elastic modulus steel (compared to concrete) at the farthest distance from the cross section increases the inertia momentum and ultimately increases the stiffness of the cross section. Concrete is an ideal core for gravity load bearing and delays local buckling of steel box and in some cases, it eliminates the local buckling altogether. It is very useful to use the CFT cross section as columns subject to severe compressive loads. Compared to concrete columns with dense concrete columns, the steel tube can prevent concrete cracking. In other words, the congestion of the reinforcement is eliminated, especially in the connection areas, which is very useful in seismic considerations (Tables 3.2.61 and 3.2.62). An example of a metal jacket design calculation for one of the critical pillars in this project is provided (Tables 3.2.63 and 3.2.64) t 5 0:8 cm;

le 5 285 cm;

fy 5 2400 kg=cm2 As 5 ð60:82 2 602 Þ 3

De 5 60:8 cm;

π 5 75:9 cm2 ; 4

fcu 5 280 kg=cm2 ;

Ac 5 602 3

π 5 2827 cm2 4

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Table 3.2.61 Regulations for CFT columns with the criteria provided in the BS54002005.

The compressive strength of concretefilled sections Nu 0:95As f 0y 1 0:45AC fCC

The fCC characteristic of enclosed concrete is obtained by the following relation fCC 5 fCu 1 C1 Dt e fy

fy Reduced nominal yield stress of steel wall is equal to: f 0y 5 C2 fy

Table 3.2.62 C1 and C2 are the coefficients obtained from the by-law table and De is the outer wall diameter and the wall thickness t. Le =De C1 C2

0 5 10 15 20 25

9.47 6.40 3.81 1.80 0.48 0

0.76 0.80 0.85 0.90 0.95 1.0

Table 3.2.63 Column element details (summary). Level Element Section Column compressive capacity Length (mm)

STORY12 C102

C60-16T22 699 ton

3500

Table 3.2.64 Pu, Mu2, Mu3. Design Pu tonf

Design Mu2 tonf-m

Design Mu3 tonf-m

540/2985

17/9595


7/8208

c1 5 6:4 le 0 5 4:69; 5-fy 5 c2 fy 5 0:8 3 2400 5 1920 kg=cm2 De c2 5 0:8 fcc 5 fcu 1 c1

t t 0:8 3 2400 5 482 kg=cm2 fy 5 fcu 1 c1 fy 5 280 1 6:4 3 De De 60:8 0

Nu 5 0:95fy As 1 0:45fcc Ac 5 ½0:95 3 1920 3 75:9 1 0:45 3 482 3 2827 1 0:8 3 4000 3 60:79 5 946147 kg 5 946 ton As can be seen, the compressive capacity of the column increased from 699 to 649 ton by about 35%, in which case the reinforcement of columns with grade 37 steel with a thickness of 8 mm is permissible.

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Shear force transfers between the metal jacket and the concrete column, a shear-head section must be used, in: Vu 5 Pu ðFy As =Pno Þ-Vumax 5 Fy As 5 2400 3 ð60:82 2 602 Þ 5 182; 070 kg This shear must be tolerated by shear stud nude placed between concrete column and steel jacket. The amount of design longitudinal shear strength (RC) is determined through the following equation: X X X Rc 5 Qcv 5 fQnv 5 0:65Fu Asa Considering steel sheets with dimensions of 20 3 50 3 20 mm and 4 pcs/m, the number of shears required along the column is: X 0:65Fu Asa 5 ð0:65 3 3700 3 5 3 2Þ 3 4 5 96; 200 X kg-n 5 Vu =ð0:65Fu ASa Þ 5 182; 070=96; 200D2 As a result, at column length there must be at least two rows of four shear stud. Fig. 3.2.104 is an example of steel jackets during building and after installation. Further, the related calculations are presented Calculating required strength for the load applied on enclosed concrete: Nu  2 f f A S y St 0:8 fCC 5 -fCC 5 33:20 Mpa 0:85ϕC ðAg 2 ASt Þ Relative calculation of mass strength:

fCC 2 1 fC Ww 5 -Ww 5 0:32 αPC

Figure 3.2.104 Details of concrete pillar cover with steel sections.

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Calculation of the required enclosure: ww φC fC f1frp 5 2

or

!

fC 1 2 φC f1frp # 2αPC Ke

- f1frp 5 4

Calculating the required number of FRP layers Nb 5

f1frp Dg -Nb 5 1:73D2 2φfrp ffrpu tfrp

Calculation of coefficient of compressive strength of column with enclosure FRP flfrp 5

2Nb ffrp φfrpu tfrp -flfrp 5 4:61 MPa Dg

fCC 5 fC ð1 1 αPC ww Þ-fCC 5 40:35  Nrmax 5 0:8 φc fcc ðAg 2 Ast Þ 1 φS fy Ast -Nrmax 5 9240 KND925 ton The increase in compressive capacity is from 699 to 924 ton, which is 1.32 times the initial capacity. Evaluating the structure of the foundation of the building and its interaction with the soil under foundation. 3.2.6.2.43 Expected soil capacity One of two EMA 356 structural studies prescription methods can be used to calculate the expected bearing capacity of foundation soil. 1. If the building technical documentation or geotechnical studies report is available for the site and contains information on the design parameters of the foundations, the expected prescribed bearing capacity shall be calculated by the following relation for surface foundation: qC 5 3qa , where qa is the authorized bearing capacity listed in the technical documentation available for surface foundations under gravity loads. 2. If the building technical documentation or geotechnical studies report is not available for the site in question, it is recommended to calculate the expected prescribed load capacity of the surface foundations for the building from the following relation. In the following formula QD is the building load and A is the foundation basement: qc 5 1:5QD =A. In the case of structural studies, subsurface geotechnical studies should be carried out to calculate the expected (final) load capacity of the foundation based on the detailed specifications of the building site. However, using structural bearing capacity is preferable to prescriptive bearing

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capacity. Since the structural studies have been carried out for the structure in question, the geotechnical report and according to the type of foundation, the permissible soil bearing capacity is 4.11 kg/cm2. 3.2.6.2.44 Modeling the existing foundation Computer modeling can be used to model the foundation. The amount of supports reactions calculated in the final nonlinear modeling for gravity and seismic loads are considered in the foundation evaluation. The existing foundation structure is modeled on the computer based on diggings, technical documentation as well as geotechnical reporting. Also, the structure characteristics of the foundation are used in the modeling according to the information in the initial studies as described in Table 3.2.65. For better evaluation, it is recommended that the foundation concept be divided into longitudinal and transverse strips with the same area (Fig. 3.2.105). 3.2.6.2.45 Foundation evaluation According to FEMA 356, foundation evaluation includes soil evaluation and foundation structural evaluation, which in all the relationships associated with these evaluations, equals m for LS performance level 3. Also, the awareness factor or K in this project is considered to be 1. Table 3.2.65 Table of existing foundation Type of Foundation Expected compressive foundation thickness strength ðcmÞ ðkg=cm2 Þ

properties. Minimum compressive strength ðkg=cm2 Þ

Average permissible soil stress ðkg=cm2 Þ

Basement factor

MAT

353

4.11

0.82

150

377

Figure 3.2.105 The geometric shape of the foundation.

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Table 3.2.66 m use for analysis the foundation. Performance levels IO

LS

CP

m (value)

3

4

1.5

3.2.6.2.46 Evaluation of soil and foundation of the structure According to the criteria of Chapter 4 of FEMA 356 Journal, because the structural support is considered rigid and is not modeled on the basic structural model of the foundation, subsequent soil behavior is assumed to be deformation controlled. Soil evaluation under its foundation is controlled through subsoil. The value of m coefficients is extracted from Table 3.2.66. QUD QUD kg # 1# 1-QUD , 24:66 2 cm 2KmQC 2 3 1 3 3 3 ð4:11Þ The load components are in accordance with the load components presented in the linear section. 3.2.6.2.47 Foundation structure evaluation The behavior of foundation against applied forces is assumed to be force controlled and for evaluating it, forces resulted from linear analysis must be decreased to real forces level QUF according to the following: QUF 5 QUD =m. Therefore considering the above relationship, the combination of force-control loads is introduced. In this respect, the coefficient m is 3 (Fig. 3.2.106). Case 1:

1:1ðQD 1 QL Þ 6 QE m

and

Case 2:

0:9ðQD Þ 6 QE : m

3.2.6.2.48 Results of the foundation analysis After modeling and analyzing the foundations, the results are compared with the status of the subfoundation soil as well as the foundation structure, and the capacity of the existing structure with the required capacity obtained from the design using new forces. 3.2.6.2.49 Analysis results for soil stress The stress status of the foundation under deformation-controlled load combinations is presented. As it is seen, stress under the soil is less than the permissible value, that is, 24.66 kg/cm2 (Fig. 3.2.107).

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433

Figure 3.2.106 How to model the existing foundation.

Figure 3.2.107 Stress result of foundation evaluation.

Figure 3.2.108 Check composition of reinforcement after evaluation.

3.2.6.2.50 Investigation of foundation structure After examination in a number of design strips, the existing foundation does not have enough strength due to lack of reinforcement. These parts must be strengthened with an appropriate rehabilitation method. However, overall situation of the foundation structure is evaluated and considered relatively suitable (Fig. 3.2.108).

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Figure 3.2.109 An overview of the seismic rehabilitation of the existing building for example 02.

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435

3.2.6.2.51 Conclusions from the foundation examination Regarding the secondary shear wall attachment system for the rehabilitation of the existing structure, it is considered that in the implementation of the adjoining shear wall structure, the foundations are vulnerable and should be appropriately rehabilitated. Seismic rehabilitation in the joint area of the new concrete shear walls and existing foundations is by demolition of the upper part of the joint section and construction of new foundations. The attached maps show how to improve seismic activity (Fig. 3.2.109).

References [1] American Federal Emergency Management Agency (FEMA.356), Prestandard and Commentary for the Seismic Rehabilitation of Buildings, Reston, VA, November 2000. [2] Islamic republic of Iran Vice Presidency for Strategic Planning and Supervision: (code. No.360) first revision,Instruction for Seismic Rehabilitation of Existing Buildings, Office of Deputy for Strategic upervision, Tehran, 2014. [3] American Concrete Institute: (ACI 318/14), Building Code Requirements for Structural Concrete, Farmington Hills, 2014. [4] Federal Emergency Management Agency (FEMA) (1997), NEHRP Commentary on the Guidelines for the Seismic Rehabilitation of Buildings (FEMA 274), Reston, VA. [5] Islamic Republic of Iran Management and Planning Organization: (code.No.376), Instruction for Seismic Rehabilitation of Existing Unreinforced Masonry Buildings, Office of Deputy for Technical Affairs, Tehran, 2007. [6] Federal Emergency Management Agency (FEMA) (2000), Prestandard and Commentary for the Seismic Rehabilitation of Buildings. [7] Iran Road, Housing & Urban Development Research Center (Iranian Standard. 2800), Forth Edition of Building Design Codes against earthquake, Tehran, 2015.

Further reading American Society of Civil Engineers American Society of Civil Engineers (ASCE/SEI 710), Minimum Design Loads for Buildings and Other Structures, Reston, VA, 2010. ASCE, 2013 ASCE, Seismic Rehabilitation of Existing Buildings (ASCE/SEI 41-13), American Society of Civil Engineers,, Reston, VA, 2013.

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Concrete structure building seismic rehabilitation at a glance

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437

SUBCHAPTER 3.3

Steel structure frame buildings Aims By reading this chapter, you are introduced to • getting acquainted with all types of steel structure buildings, • getting acquainted with the methodology of evaluation of different types of steel structure buildings, • understanding the methodology of brace and steel shear wall evaluation, • learning about seismic rehabilitation methods, and • understanding the chapter topics in depth by studying two practical examples at the end of this chapter.

3.3.1 Types of steel structure frame buildings It is a type of structure whose main materials used for bearing and transporting forces are made of steel. The connections used in these types of structures are welded, riveted, or bolted, depending on the type of joints, designed components, and related controls are executed on them. Steel is now one of the most important building materials for bridges and other fixed structures. The yield strength of the steel used is in the range of 36
58 Ksi, which is used for ordinary buildings of steel with the resistance of 36 Ksi is called mild steel. Steel frame is a term used in the construction of buildings with steel vertical columns and steel horizontal beams that are connected in a structure. Usually used types of steel braces, concrete, or steel shear walls and in suitable connections to restraining seismic forces. This frame is responsible for the maintenance of floors, ceilings, and walls that are attached to the building’s structure. The development of this technology has made skyscrapers building [1
3] (Fig. 3.3.1). Steel structures can be divided into four main groups: • Framed structures: these structures often include a set of columns and beams. • Shell structure consists of a continuous sheet with special geometric shapes such as a sphere and a cylinder. • Suspension structure: the tensile force is dominant in the members of this structure.

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Figure 3.3.1 An example of a prefabricated steel structure - Urmia Lake Bridge is being moved for installation and assembly.

•

Truss structure: the members of this structure also tolerate tensile and compressive forces.

3.3.1.1 Framed structures These structures are a combination of columns and beams that are bonded together using partially or fully restrained moment frames (FRMFs) according to connection methods. Frame structures can be either industrial buildings or multistory buildings. Most modern buildings now have steel frame structure. In general, framed structures are a combination of two series of perpendicular frames that lead to the formation of a spatial frame. The next two figures show examples of multistory buildings with a framed skeleton. The building frames must also be able to tolerate vertical and lateral forces. Another example of framed structures is bridges, which are shown in the following illustrations (Figs. 3.3.2 and 3.3.3).

3.3.1.2 Shell structures Shell structures are used in various forms to build important structures such as pressurized fluid containers, cupola, silos and the like. An example of a shell structure is shown in Fig. 3.3.4.

Types of existing buildings: detailed introduction and seismic rehabilitation

Figure 3.3.2 The frame structure of factory building with light industrial cover.

Figure 3.3.3 Frame structure of a multistory building.

Figure 3.3.4 Shell structure of fluid reservoirs.

439

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Figure 3.3.6 Truss structural sample (Tehran Tabiat Bridge).

3.3.1.3 Suspension structures These types of structures are used in high-span bridges and in the cover design (high-span roofs). In this model of structures, there is a framed skeleton suspended by pendants from the main extension cables. These structures are widely used in the construction of suspension bridges. They can also be used on roof skeletons or bridge deck covers (Fig. 3.3.5).

3.3.1.4 Truss structures A set that transfers forces by means of a triangular combination of members with a simple connection to the supports is called a truss. In the members of the truss structure, only the tensile and compressive axial force are generated, but in practice, there may be a slight flexural tension between the connections due to their friction and the loads applied to the members, which of course can be ignored. Fig. 3.3.6 shows an example of a truss structures.

3.3.2 Understanding potential structural damage Structural steelwork frame buildings are highly resilient and have appropriate strength if properly designed and correctly executed, but mainly due to the lack of expert executive forces and the wrong assumptions of steel constructions construction and selection for irrelevant geographical conditions have disadvantages and drawbacks that need seismic rehabilitation. Steel structures often suffer from seismic loads due to local

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441

Figure 3.3.5 Sample of suspension structure—Tabriz Cable Bridge.

buckling and poor performance and may also require seismic rehabilitation due to corrosion. Major weaknesses and injuries in beams and columns include local and general buckling and breakage at the gaps and splices. These damages that indicate the need for seismic rehabilitation of steel members include: lack of cross-sectional area, thinness beyond the permissible limit, noncompression cross-section, weakening of welded, and noncompliance with principle of weak beams and strong columns, rust and corrosion of members, heat-affected zone due to excessive welding, fatigue, fire, abnormal deflection in beams, and deviation of column centrality over standard dimensions. Some of the damages that an engineer might encounter while seismic rehabilitation of a steel moment frame structure, include lack of shear and flexural strength of beams, columns and connections, lack of resistance at panel zone and connections, and high relative displacement in the building stories. In addition, damages caused by weaknesses in the bracing systems include: lack of lateral resistance of the brace system due to compressive buckling, lack of brace connection strength, lack of axial strength in the beams and columns of bracing system, bracing geometry that results in extra tensile stress, and bending of the beam or column by buckling of the compression member. In general, concoctions play a significant role in steel structures. Weaknesses in the connections can be considered as the inadequacy of the welds, the lack of bolts, and also the weaknesses in the connections as the most important damage at the time of seismic evaluation of building.

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3.3.3 Rapid vulnerability assessment The performance is similar to that of concrete buildings, except that the characteristics of structural steelwork frame buildings are considered in this type of evaluation For example, lateral systems to cope with seismic loading in concrete structures replace the lateral systems provided in steel buildings [2,4].

3.3.4 Comprehensive assessment of vulnerabilities for existing building with steel structure Since many steel structures may have been reinforced over time, this chapter presents content that incorporates the acceptance criteria and criteria for reinforced steel components and existing structures. Seismic rehabilitation of steel structures is the analysis and evaluation of seismic rehabilitation of all steel components of that structure including beams, columns, and connections.

3.3.4.1 Determining the specifications of materials The specification of materials required for evaluation in seismic rehabilitation of structural steelwork frame buildings is the determination of Fu , Fy , and E for all components studied in the seismic rehabilitation process. These specifications, as noted in the previous chapters, are calculated from the test results [1,2]. 3.3.4.1.1 The low-bound specifications of materials The details of the low-bound specifications of the materials are obtained according to the computational manuals, the existing plans and tests performed at implementation, and the documentation collected at implementation. 3.3.4.1.2 Expected material specifications The expected specifications of the materials are determined by the mean values obtained from the tests. Another way to determine the expected specifications of the materials is by using the following equation Expected case 5 1:1 3 ð lower-bound specificationÞ.

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443

3.3.4.2 Number of tests required at least based on seismic rehabilitation objectives As this Tests and Digging has been thoroughly evaluated and studied in Chapter 2, What is the seismic rehabilitation? Introduction practical method for seismic rehabilitation of existing building, it is presented in the following flowchart to remind the reader of conventional and comprehensive tests for use [2,5,6] (Fig. 3.3.7 and Table 3.3.1). The American Society for Testing Materials standards are used to evaluate the specification of materials in tests.

3.3.4.3 Steel moment frames The steel moment frames studied in this section of the book are divided into two main categories based on the degree of rigidity in moment connections according to the criteria presented in the FEMA 356 Seismic

Figure 3.3.7 Chart of test needed for seismic rehabilitation of steel structure building. Table 3.3.1 Tip on digging and testing and evaluating welding strength. Steel How to evaluate welding

ST 5 37 The dimensions and length of the weld are measured at the location of each shown connection Determine the quality of welding by nondestructive tests at each connection 37 , ST The dimensions and length of the weld are measured at the location of each shown connection In this case the welding strength shall be determined by sampling the connection in addition to those specified in ST 37

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Improvement Regulations and the Iranian codec 360 for seismic rehabilitation of existing building. In Iranian seismic rehabilitation codec has been used to determine unit values of (ksc) instead of (Ksi). • Fully restrained moment frame (FRMF). • partially restrained moment frame (PRMF). Following is a complete description of each of the above structural systems by categorizing the performance evaluation methods in the linear and nonlinear domains. 3.3.4.3.1 Fully restrained moment frame The acceptance criteria of moment connections include the evaluation of the ductility of the connection, the stiffness and the strength of the connection being evaluated. The following flowchart can be used to understand and accept the rigidity of the connections. Types of connection in FRMF [1,2] • direct connection with penetrating welding, • attaching the beam flanges to the column using cover plate, • connection using end plate, • connection to the flanges separated from the beam, and • all connections that meet the rigid connection requirements (Fig. 3.3.8). 3.3.4.3.1.1 Linear analysis method (static and dynamic)

3.3.4.3.1.1.1 Determining the stiffness of the components The moment frame modeling can be done according to the stiffness of the beams and columns and the size of the center to center. To achieve more realistic results, the panel zone can be modeled. In linear analysis, if the bending moment corresponding to the expected shear strength at the panel zone is greater than the flexural strength of the beam at the connections and also the stiffness of the panel zone is more than 10 times the flexural strength of the beam, we do not need to model the panel zone in the 3D model. The bending moment calculations of the beam and the

Figure 3.3.8 Chart of assumptions of moment connections.

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445

shear force on beam are defined by the rigid element of column fixed edge. Stiffness in this case is obtained by one of the following criteria based on the strength of the materials [1,2] (Fig. 3.3.9). 3.3.4.3.1.1.2 Determining components strength 3.3.4.3.1.1.2.1 Evaluation of beams strength The beams in moment frames

usually have deformation-controlled behavior. The criteria are also for the time that the axial force created in the beams is negligible. The expected strength in the linear behavior limitation for the beam is the minimum limit of each member below. The expected strength in linear behavior limitation for beams or any member of the moment member, deformation-controlled behavior is equal to the smallest amount of yield point, lateral-torsional buckling, local flange buckling, or local web shear yielding. So that in the following figure, states of quantifying the strength of the beam are shown (Fig. 3.3.10). The resistance of members of steel structures with axial force less than 10% of the axial capacity of the member and bending stress shall be

Figure 3.3.9 Chart of stiffness required for modeling.

Figure 3.3.10 Beam simulation for modeling in computer software.

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Seismic Rehabilitation Methods for Existing Buildings

Figure 3.3.11 Chart of beam expected strength value limit state, QCE .

Figure 3.3.12 Chart of column strength.

calculated in accordance with the provisions of this paragraph [1,2] (Fig. 3.311). 3.3.4.3.1.1.2.2 Evaluation of columns strength Columns in the fully restrained (FR) moment frame have different behavior due to the type of axial force applied to the column, which can be either deformationcontrolled or force-controlled. This section deals with the evaluation of resistance in members whose axial force is greater than 10% of axial capacity. The behavior of the columns is controlled by the force acting on the pressure and by the tensile function of the deformation controlled and its resistance is calculated as follows [1,2] (Fig. 3.3.12). 3.3.4.3.1.1.2.3 Evaluation of the panel zone strength The panel zone in FR moment frames have deformation-controlled behavior and their strength is evaluated through equation [1,2]: QCE 5 VCE 5 0:55ðFye dc tp Þ

(3.3.1)

3.3.4.3.1.1.2.4 Evaluation of beam-to-column connection strength This is cal-

culated based on all limit states of the possible failure modes.

Types of existing buildings: detailed introduction and seismic rehabilitation

447

3.3.4.3.1.1.2.5 Evaluation of column base plate strength The strength of the

column base plate should be calculated for the lowest value resulted from the limit state of expected strength of bolt or weld, the expected bearing stress of the concrete beneath the base plate, and the expected yield strength of the material FYe of column floor plate [1,2] (Fig. 3.3.13). Evaluation of connection strength between base plate and concrete It should be calculated for the minimum value of the limit state of column strength, the column base plate thickness and the strength of bracing bolts. Evaluation of the boundary strength between anchor bolt and concrete It should be calculated on the basis of the minimum value resulting from limit state of shear yielding strength or tension strength or the decrease in braced length or on the basis of concrete failure modes. 3.3.4.3.1.1.3 Acceptance criteria As mentioned in Chapter 2, What is the seismic rehabilitation? Introduction practical method for seismic rehabilitation of existing building. Acceptance criteria for seismic rehabilitation are in the form of two processes controlled by deformation and force controlled [1,2] (Fig. 3.3.14). 3.3.4.3.1.1.3.1 Deformation-controlled Efforts in deformation-controlled members should be evaluated based on the following equation: mKQCE $ QUD

Figure 3.3.13 Function details of the base plate against the applied loads.

(3.3.2)

Figure 3.3.14 Acceptance criteria for force and deformation controlled components.

449

Types of existing buildings: detailed introduction and seismic rehabilitation

3.3.4.3.1.1.3.2 Force-controlled Efforts in force-controlled members should

be calculated based on the following equation: KQCL $ QUF

(3.3.3)

3.3.4.3.1.1.3.3 Acceptance criteria for beams To determine the expected

strength capacity of the beams, the parameter value m is evaluated in linear analysis method define for the four boundary states that have a direct relationship with the lateral bracing Lb of the beams (Fig. 3.3.15). In the acceptance criterion, one of the following four conditions is true for beams (Fig. 3.3.16 and Table 3.3.2). 3.3.4.3.1.1.3.4 Acceptance criteria for columns The acceptance criterion in the existing columns in the moment frames is controlled according to the axial and flexural loads in four possible states. Therefore the amount of constraints defined is measured by the ratio of external axial forces to internal axial capacity. Criteria for acceptance criteria are state (1) ðPUF =PCL Þ # 0:2 for compression and flexural, state (2) 0:2 # ðPUF =PCL Þ # 0:5 for compression and flexural, state (3) ðPUF =PCL Þ $ 0:5 for compression and flexural, and state (4) ðPUF =PCL Þ $ 0:5 for tension and flexural it is worth

Figure 3.3.15 A sample of lateral bracing span for composite roof beams.

Figure 3.3.16 Chart of selection m in different modes of lateral bracing in beams.

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Seismic Rehabilitation Methods for Existing Buildings

noting that in states 1 and 2 the comparison is force-controlled and flexural is deformation controlled and in the third state both load the forcecontrolled. In the fourth case, both tension and flexural will be controlled by the deformation [1,2] (Fig. 3.3.17 and Table 3.3.3). 3.3.4.3.1.1.3.5 Acceptance criteria for panel zone The acceptance criterion at the panel zone has a deformation-controlled effort and is calculated by design efforts to counter the shear-induced bending moment which m value is obtained, determined, and extracted from the acceptance criterion table in linear methods for structural members [1,2] (Fig. 3.3.18 and Table 3.3.4). VUD2 5 PUD1 1 PUD2 2 V

(3.3.4)

Table 3.3.2 Acceptance criteria for linear procedures—beam. Component/action unit ðKsiÞ

m-Factors for the expected performance level IO

Beams—flexurepffiffiffiffiffiffi pffiffiffiffiffiffi ðbf =2tf Þ , ð52= Fye Þ and ðh= tw Þ , ð418= Fye Þ pffiffiffiffiffiffi pffiffiffiffiffiffi ðbf =2tf Þ . ð65= Fye Þ and ðh= tw Þ . ð640= Fye Þ bf Other 2tf or thw

Primary

Secondary

LS

LS

CP

CP

2 6 8 10 12 1.25 2 3 3 4 Using linear interpolation and the smallest value obtained

Figure 3.3.17 Chart of acceptance criteria of column in such cases.

Table 3.3.3 Acceptance criteria for linear procedures—m-factor column. Component/action ðKsiÞ m-Factors for the expected performance level IO

Primary LS

pffiffiffiffiffiffi pffiffiffiffiffiffi ðbf =2tf Þ , ð52= Fye Þ and ðh= tw Þ , ð300= Fye Þ pffiffiffiffiffiffi pffiffiffiffiffiffi ðbf =2tf Þ . ð65= Fye Þ and ðh= tw Þ . ð460= Fye Þ  pffiffiffiffiffiffi pffiffiffiffiffiffi ðbf =2tf Þ , ð52= Fye Þ and ðh= tw Þ , ð260= Fye Þ pffiffiffiffiffiffi pffiffiffiffiffiffi ðbf =2tf Þ . ð65= Fye Þ and ðh= tw Þ . ð400= Fye Þ b Other 2tff or thw for both conditions

Secondary CP

Columns—flexure for ðP=PCL , 0:20Þ 2 6 8 1.25 2 3 Columns
forð0:2 , P=PCL , 0:5Þ 1.25 — — 1.25 1.25 1.5 Using linear interpolation and the smallest value

LS

CP

10 3

12 4

— 2 obtained

— 2

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Seismic Rehabilitation Methods for Existing Buildings

3.3.4.3.1.1.3.6 Connection in FR moment frame

Define condition acceptance criteria methods Moment connection for beam-to-column in FR moment frame are generally deformationcontrolled, and the value of m is extracted from the acceptance criterion table for linear-structural steel component methods according to specific criteria Also failure to observe the following criteria results in a decrease in m presented in this table: [1,2] 1. details of the continuity plate, 2. resistance of panel zone, 3. span-to-depth ratio in beam, and 4. investigate the effects of slenderness. Note: In cases where moment connection is designed to form a plastic hinge in the beam and away from the column, all limit states of connection are force controlled. Details of the continuity plate There are generally three limit states for selecting value m from the table. If the following condition is not met for the continuity plate limitation, the value of m shall be multiplied by a coefficient of 0.8 (Fig. 3.3.19). The effects of a panel zone If the following condition is not met, the m shall be multiplied by 0.8 (Fig. 3.3.20). 0:6 #

VPZ # 0:9-Vy 5 0:55FyeðcolÞ dc tcw Vy

(3.3.5)

Figure 3.3.18 Deformation of the panel zone under the applied forces. Table 3.3.4 Acceptance criteria for linear procedures—m-factor for panel zone. Component/action (Ksi) m-Factors IO

Column panel zones—shear All cases

1.5

Primary

Secondary

LS

CP

LS

CP

8

11

12

12

Types of existing buildings: detailed introduction and seismic rehabilitation

P VPZ 5

   MyðbeamÞ L h 2 db -MyðbeamÞ 5 Sfye L 2 dc db h

453

(3.3.6)

Ratio span to depth of beam If the value of the net span to beam depth is greater than 10, the values of m in the acceptance criterion in the linear-structural steel component methods must be multiplied by the extraction coefficient from relation [1,2] (Fig. 3.3.21).   Le 1:4 2 0:04 (3.3.7) d Slenderness effects in acceptance criteria Whenever the ratio of the slenderness values in the following equations is true, there is no need to change the value of m. bf 52 , pffiffiffiffiffiffi ; 2tf Fye

h 418 , pffiffiffiffiffiffi tw Fye

Figure 3.3.19 Chart and shape of detail for the continuity plate.

Figure 3.3.20 Continuity plate and its effect on panel zone.

(3.3.8)

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Seismic Rehabilitation Methods for Existing Buildings

Figure 3.3.21 Ratio span to depth of beam.

Whenever the ratio of the slenderness values in the following equations is not true, the coefficient m-factor must be multiplied by 0.5. bf 65 . pffiffiffiffiffiffi ; 2tf Fye

h 640 . pffiffiffiffiffiffi tw Fye

(3.3.9)

Accept criteria of connection in FR moment frame This section is presented in 12 categories to better understand the concepts of FR moment connections. Finally according to the stated conditions, you can extract the value of m from Table 3.3.5 and use it in the calculations [1,2] (Figs. 3.3.22 and 3.3.23). 3.3.4.3.1.1.3.7 Connection between the foundation and base plate For yielding the base plate, bolt and welding fracture, the values of m given in the acceptance criterion table in linear-structural steel component methods can be used to bond the semirigid connection to the end plate depending on the corresponding limit state. If the limiting state of the foundation and base plate connection is controlled by the reinforced concrete failure modes, the force-controlled behavior shall be taken into connection [1,2] (Fig. 3.3.24). 3.3.4.3.1.2 Nonlinear (static and dynamic) analysis and evaluation method

3.3.4.3.1.2.1 Nonlinear static analysis method 3.3.4.3.1.2.1.1 Determining the stiffness of the components In the nonlinear

method, the force and deformation curves are used. In this case, the nonlinear diagram parameters values are extracted from the tables in applied tables section [1,2] (Fig. 3.3.25). Note: In nonlinear analysis, if the moment corresponding to the expected shear strength at the panel zone is greater than the flexural strength of the

Table 3.3.5 Accept criteria in linear methods of m-factor for connection in fully restrained (FR) moment frame. m-Factors Component/action (Ksi)

IO

Primary

Secondary

LS

CP

LS

CP

4.3
0.083d 2.7 2.1 4.3
0.067d 2.30.021d 4.2 6.3
0.098d 4.9
0.025d

3.9
0.043d 3.4 2.5 5.4
0.090d 3.1
0.032d 5.3 8.1
0.129d 6.2
0.032d

4.3
0.048d 3.8 2.8 5.4
0.090d 4.9
0.048d 5.3 8.4
0.129d 6.5
0.025d

5.5
0.064d 4.7 3.3 6.9
0.118d 6.2
0.065d 6.7 11.0
0.172d 8.4
0.032d

4.1

5.7

7.3

3.8 3.9 3.4

4.6 4.7 3.4

5.9 6.0 4.2

Fully restrained moment connections

1. WUF 2. Bottom haunch in WUF with slab 3. Bottom haunch in WUF without slab 4. Welded cover plate in WUF 5.Improved WUF-bolted web 6. Improved WUF-welded web 7. Free flange 8. Reduced beam section 9. Welded flange plates a. Flange plate net section b. Other limit states 10. Welded bottom haunch 11. Welded top and bottom haunches 12. Welded cover-plated flanges WUF, welded unreinforced flange.

1.0 1.6 1.3 2.4
0.030d 1.4
0.008d 2.0 2.7
0.032d 2.2
0.008d

1.7 3.3 Force controlled 1.6 3.1 1.6 3.1 1.7 2.8

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Seismic Rehabilitation Methods for Existing Buildings

Figure 3.3.22 Accept criteria of connection in FR moment frame part one.

Figure 3.3.23 Accept criteria of connection in FR moment frame part two.

Types of existing buildings: detailed introduction and seismic rehabilitation

457

Figure 3.3.24 Connection between the foundation and base plate.

Figure 3.3.25 Definition of chord Rotation for evaluation the stiffness in nonlinear method.

beam at the joint and also the stiffness of the panel zone is more than 10 times the flexural strength of the beam, we do not need to model the coupling spring in the 3D model. The basis of the bending beam anchor and beam shear calculations is to define the rigid element from the column. For beams: θy 5

ZFye lb -QCE 5 MCE 5 MPCE 5 ZFye 6EIb

(3.3.10)

For columns:

  ZFye lc P -QCE 5 MCE 5 1:18ZFye 1 2 θy 5 Pye 6EIc

(3.3.11)

Panel zone QCE 5 VCE 5 0:55Fye dC tP

(3.3.12)

3.3.4.3.1.2.1.2 Determination of strength of components In this method, the

force
displacement diagram according to the following figure should be

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Seismic Rehabilitation Methods for Existing Buildings

evaluated and extracted for each component based on the criteria clause presented in the stiffness evaluation section in the nonlinear behavior range. The expected strength values show as QCE , and the lower bound strength threshold, QCL , are also determined for the steel components as provided for the linear range of member strength evaluation. 3.3.4.3.1.2.1.3 Strength evaluation tips include:

• • • •

Determine the strength of each component based on the values of the deformation and the shear-controlled behavior of the shear and flexural, similar to the methods presented in the analysis and linear behavior range. The expected strength to the components has a deformation controlled behavior. Lower bound strength use for components which force control behavior. The knowledge factor for new components is always considered 1.

3.3.4.3.1.2.2 Nonlinear dynamic method In the nonlinear dynamic method, the complete cyclic behavior of each component should be appropriately modeled based on the test results. 3.3.4.3.1.2.3 Acceptance criteria The values of the deformations and forces of the components with the behavior controlled by deformation and force are calculated from nonlinear analysis of the members. In the forces controlled by the forces, the forces obtained from the analysis must be lower than the lower bound of the desired effort. In components with deformation-controlled behavior, the deformations resulting from the analysis must be smaller than the permitted deformation in Tables 3.3.6
3.3.9 presented for the selected performance level [1,2] (Fig. 3.3.26). Table 3.3.6 Accept criteria in nonlinear method to define pushover curve for panel zone. Component/ action

Column panel zones

Modeling parameters

Acceptance criteria

Plastic rotation angle (radians)

Residual strength ratio

Plastic rotation angle (radians)

a

b

c

12 θy

12 θy

1.0

IO

1 θy

Primary

Secondary

LS

CP

LS

CP

8 θy

11 θy

12 θy

12 θy

Table 3.3.7 Accept criteria in nonlinear method to define pushover curve for beams. Component/action Modeling parameters Plastic rotation angle (radians)

Residual strength ratio

a

c

b

Acceptance criteria Plastic rotation angle (radians) IO

Primary LS

Secondary CP

LS

CP

9 θy 3 θy

11 θy 4 θy

Beams—flexure

pffiffiffiffiffiffi pffiffiffiffiffiffi ðbf =2tf Þ , ð52= Fye Þ and ðh= tw Þ , ð418= Fye Þ pffiffiffiffiffiffi pffiffiffiffiffiffi ðbf =2tf Þ . ð65= Fye Þ and ðh= tw Þ . ð640= Fye Þ b Other 2tff or thw for both conditions

9 θy 11 θy 0.6 1 θy 6 θy 8 θy 4 θy 6 θy 0.2 0.25 θy 2 θy 3 θy Using linear interpolation and the smallest value obtained

Table 3.3.8 Accept criteria in nonlinear method to define pushover curve for columns. Component/action Modeling parameters Plastic rotation angle (radians)

Residual strength ratio

a

b

c

9 θy 4 θy

11 θy 6 θy

0.6 0.2

11α 1 θy

17α 1.5 θy

0.2 0.2

Acceptance criteria Plastic rotation angle (radians) IO

Primary

Secondary

LS

CP

LS

CP

1 θy 0.25 θy

6 θy 2 θy

8 θy 3 θy

9 θy 3 θy

11 θy 4 θy

0.25 θy 0.25 θy

14α 0.5 θy

11α 0.8 θy

14α 1.2 θy

17α 1.2 θy

Columns—flexure

For ðP=PCLÞ ,p 0:20 pffiffiffiffiffiffi ffiffiffiffiffiffi ðbf =2tf Þ , ð52= Fye Þ and ðh= tw Þ , ð300= Fye Þ pffiffiffiffiffiffi pffiffiffiffiffiffi ðbf =2tf Þ . ð65= Fye Þ and ðh= tw Þ . ð460= Fye Þ For 0.2 , P/PCL , 0.50 pffiffiffiffiffiffi pffiffiffiffiffiffi ðbf =2tf Þ , ð52= Fye Þ and ðh= tw Þ , ð260= Fye Þ pffiffiffiffiffiffi pffiffiffiffiffiffi ðbf =2tf Þ . ð65= Fye Þ and ðh= tw Þ . ð400= Fye Þ α 5 ð1 2 1:7P=PCL Þθy b Other 2tff or thw for both conditions

Using linear interpolation and the smallest value obtained

Table 3.3.9 Accept criteria in nonlinear method to define pushover curve for connections. Component/action

Fully restrained moment connections WUF Bottom haunch in WUF with slab Bottom haunch in WUF without slab Welded cover plate in WUF Improved WUF-bolted web Improved WUF-welded web Free flange Reduced beam section Welded flange plates 1. Flange plate net section 2. Other limit states Welded bottom haunch Welded top and bottom haunches Welded cover-plated flanges

Modeling parameters

Acceptance criteria

Plastic rotation angle (radians)

Residual strength ratio

a

b

c

0.051
0.0013d 0.026 0.018

0.043
0.2 0.0006d 0.036 0.2 0.023 0.2

0.0128
0.0337
0.0284
0.0003d 0.0009d 0.0004d 0.0065 0.0172 0.0238 0.0045 0.0119 0.0152

0.0323
0.043
0.0005d 0.0006d 0.0270 0.036 0.0180 0.023

0.056
0.0011d 0.021
0.0003d 0.041 0.067
0.0012d 0.050
0.0003d

0.056
0.0011d 0.050
0.0006d 0.054 0.094
0.0016d 0.070
0.0003d

0.0140
0.0003d 0.0053
0.0001d 0.0103 0.0168
0.0003d 0.0125
0.0001d

0.0319
0.0006d 0.0139
0.0002d 0.0312 0.0509
0.0009d 0.0380
0.0002d

0.0426
0.0008d 0.0210
0.0003d 0.0410 0.0670
0.0012d 0.0500
0.0003d

0.0420
0.0008d 0.0375
0.0005d 0.0410 0.0705
0.0012d 0.0525
0.0002d

0.056
0.0011d 0.050
0.0006d 0.054 0.094
0.0016d 0.07
0.0003d

0.2

0.0075

0.0228

0.0300

0.0450

0.06

0.2 0.2 0.2

0.0068 0.0070 0.0078

0.0205 0.0213 0.0177

0.0270 0.0280 0.0236

0.0353 0.0360 0.0233

0.047 0.048 0.031

0.03 0.06 Force-controlled 0.027 0.047 0.028 0.048 0.031 0.031

0.2 0.2 0.2 0.2 0.2

Plastic rotation angle (radians) IO

Primary LS

Secondary CP

LS

CP

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Seismic Rehabilitation Methods for Existing Buildings

3.3.4.3.2 Partially restrained moment frame If the connection does not meet the acceptance criteria for FR moment frame, it is considered to be a PR moment frame. In general, rigid joints fall into two groups [1,2]: • Connection to the top and bottom angles. • Up and down T- section connection using Bolt or rivet to column flanges and beam flange. • Connection with low-capacity plate in up and down components. • It is worth noting that typically PRMF with bolt joints have better earthquake performance than PRMF with welded joints. An example of these studies is shown in Fig. 3.3.27.

Figure 3.3.26 Acceptance criteria for nonlinear analysis method.

Figure 3.3.27 Different between FR and PR connections.

Types of existing buildings: detailed introduction and seismic rehabilitation

463

3.3.4.3.2.1 Linear analysis method (static and dynamic)

3.3.4.3.2.1.1 Determining the stiffness of components 3.3.4.3.2.1.1.1 Connection node The stiffness value of Kθ for each semirigid connection is evaluated by one of the following methods [1,2]: • based on experiments and • with proper analysis. For example, the approximate method below the stiffness of the connecting node can be determined by considering MCE “expected moment restrain.” In this case Kθ is equal200MCE . PR moment frame connections enclosed in concrete. The following equation is used to calculate the anchor due to its complex performance. In this case Kθ is equal 334MCE . Instead of using a precise analytical model of the PR moment frame, as an approximation method in the modeling, the frame can be FR moment frame provided that the stiffness of the beams is corrected by the following equation (Fig. 3.3.28). 3.3.4.3.2.1.2 Determination of strength of components This section defines resistors to determine the strength for members and connections. 3.3.4.3.2.1.2.1 Components strength The strength of steel beams and columns PR moment frames, which are analyzed as linear methods, is based on the criteria presented in FR moment frames: [1,2] 3.3.4.3.2.1.2.2 Connections The strength of the semirigid connections should be based on tests. Also if the results of the experiments are not available, the expected resistance value of the semirigid connection in PRMF can be calculated for each of the limit states given below. 1. connection with top and bottom clip angle, 2. connection with using double split Tee-section,

Figure 3.3.28 EIb adjusted.

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Seismic Rehabilitation Methods for Existing Buildings

Figure 3.3.29 Chart of limit states for the semirigid connection in PRMF. PRMF, Partially restrained moment frame.

3. connection with bolted flange plate, 4. connections with bolted end plate connections, and 5. composite partially restrained connections (Fig. 3.3.29). Connection with top and bottom clip angle This connection is used by the top and bottom clip angles and by the use of bolts or rivets to connect the beam to the column. The expected moment strength of the connection MCE is the smallest of the four limit states expressed below this bending moment. Limit state one Shear the joints between the beam flanges and the flange of angle controls the strength of the connection. Second limit state If the tensile capacity of the horizontal leg of the connection controls the capacity. Third limit mode If the tensile capacity of the rivets or bolts attaching the vertical outstanding leg to the column flange controls the capacity of the connection. Fourth limit mode The flexural yielding capacity the vertical flange of angle to the column flange controls the connection capacity (Fig. 3.3.30). Connection with using double split Tee-section In this connection, the upper and lower Tee-sections are attached to the flanges of column with bolt or rivets as shown below, and the flanges of the beam are connected to the Tee-section by bolts or rivets or welding. The moment is, in this case, the smallest value calculated from the following four limit states. Limit state one If the shear connectors between the beam flange and the web of the Tee-section control the capacity of the connection.

Types of existing buildings: detailed introduction and seismic rehabilitation

465

Figure 3.3.30 Chart of evaluation for connection with upper and bottom angle.

Figure 3.3.31 chart of evaluation for connection between beam and column by T section.

Second limit state If the tension capacity of the bolts or rivets connecting the flange of Tee-section to the column flange control the capacity of the connection Third limit mode If tension in the stem of the Tee-section controls the capacity of the connection. Fourth limit mode If flexural yielding of the flanges of the split tee controls the capacity of the connection (Fig. 3.3.31). Connection with bolted flange plate In this connection, the flange plate is attached to the column flange by means of full penetration welding and is connected to the beam by bolt or rivet or welding. The expected strength, in this case, is the smallest value calculated from the following three limit states. Limit state one In this case, the shear strength of the connecting devices between the beam flange and the connecting plate controls the connection resistance.

466

Seismic Rehabilitation Methods for Existing Buildings

Figure 3.3.32 Chart of evaluation for connection between beam and column by top plate connection.

Second limit state The tensile capacity of the connection plate is the controller of the connection resistance. Third limit mode The welding of the plate is connected to the flange of the column which controls the resistance of the connection (Fig. 3.3.32). Connections with bolted end plate connections In this connection the plate is connected to the beam cross-section by means of full penetration welding or corner welding and then by bolt to the flange of the column. The strength in this connection is equal to the smallest of the three limit states of the end plate, bolt yielding, and welding. Limit state one In this type of limiting state, the bolts are force controlled and the lower bound of this strength is calculated based on the limiting state of the connection pulling and shearing effect. In the frictional connections, the restrained force in slipping rs for each bolt multiply the coefficient of decrease α. Second limit state In this connection the bending in the plate is controlled by the deformation and the expected strength resulting from this state is calculated by a logical analysis from AISC 358 (Fig. 3.3.33). Composite partially restrained connections Strength and deformation acceptance criteria of composite partially restrained connections shall be based on approved rational analysis procedures and experimental evidence (Table 3.3.10). 3.3.4.3.2.1.3 Acceptance criteria 3.3.4.3.2.1.3.1 Acceptance criteria for primary members Principles can be

applied to core members, such as beams and columns for steel constructions that have been analyzed using linear methods in the elastic range.

Types of existing buildings: detailed introduction and seismic rehabilitation

467

Figure 3.3.33 Chart of evaluation for connection between beam and column by end plate connection.

3.3.4.3.2.1.3.2 Acceptance criteria for connections This parameters for PR

moment frames is extracted from the tables according to the m value of each of the limit states of the semirigid connections and evaluated according to the criteria. Case 1: partially restrained moment connection with top and bottom clip angle method (Table 3.3.11). Case 2: partially restrained moment connection with double split tee method (Table 3.3.12). Case 3: partially restrained moment connection with bolted flange plate method (Table 3.3.13). Case 4: partially restrained moment connection with bolted end plate method (Table 3.3.14). Case 5: partially restrained moment connection with composite methods (Table 3.3.15). 3.3.4.3.2.2 Nonlinear (static and dynamic) analysis and evaluation method

3.3.4.3.2.2.1 Determining of stiffness of components 1. Nonlinear static method of stiffness determination in PR moment frames To express the properties of the nonelastic range of beams, columns and panel zone, the force
displacement curve with the values of a, b, and c in the tables should be used, like FR moment frames. 2. Nonlinear dynamic method for determination of stiffness in PR moment frames. The complete cyclic behavior of each component is appropriately modeled on the basis of the test results [1,2]:

Table 3.3.10 The nominal tensile stress Ft, in shear connections. The shear section is outside the thread (kg/cm2)

8070 2 2:0fv # 6200 9800 2 2:0fv # 7500 0:98Fue 2 2:0fv # 0:75Fue

The shear section passes through the threaded section (kg/cm2)

Type of connector

4100 2 2:5fv # 3150 8070 2 2:5fv # 6200 9800 2 2:5fv # 7500 0:98Fue 2 2:5fv # 0:75Fue 0:98Fue 2 2:4fv # 0:75Fue

The usual bolt A325 bolt A490 bolt Threaded piece Rivet

469

Types of existing buildings: detailed introduction and seismic rehabilitation

Table 3.3.11 Acceptance criteria for linear procedures (PR) moment connections case 1. Component/action m-Factors IO

Shear failure of rivet or bolt (limit state 1) Tension failure of horizontal leg of ngle (limit state 2) Tension failure of rivet or bolt (limit state 3) Flexural failure of angle (limit state 4)

Primary

Secondary

LS

CP

LS

CP

1.5

4

6

6

8

1.25

1.5

2

1.5

2

1.25

1.5

2.5

4

4

2

5

7

7

14

Table 3.3.12 Acceptance criteria for linear procedures (PR) moment connections case 2. Component/action m-Factors IO

Shear failure of rivet or bolt (limit state 1) Tension failure of rivet or bolt (limit state 2) Tension failure of split tee stem (limit state 3) Flexural failure of split tee (limit state 4)

Primary

Secondary

LS

CP

LS

CP

1.5

4

6

6

8

1.25

1.5

2.5

4

4

1.25

1.5

2

1.5

2

2

5

7

7

14

3.3.4.3.2.2.2 Determination of strength of components In this method, the force
deformation relation according to the following figure, as well as the FR moment frame criteria, shall be evaluated and extracted for each component based on the criteria clause provided in the stiffness evaluation section in the nonlinear behavior range. 3.3.4.3.2.2.3 Acceptance criteria The acceptance criterion for members forming a PR moment frame is the same as the criteria for acceptance for the FR moment frame [1,2]: Case 1: partially restrained moment connection with top and bottom clip angle method (Table 3.3.16).

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Seismic Rehabilitation Methods for Existing Buildings

Table 3.3.13 Acceptance criteria for linear procedures (PR) moment connections case 3. Component/action m-Factors IO

Failure in net section of flange plate or shear failure of bolts or rivets Weld failure or tension failure on gross section of plate

Primary

Secondary

LS

CP

LS

CP

1.5

4

5

4

5

1.25

1.5

2

1.5

2

Table 3.3.14 Acceptance criteria for linear procedures (PR) moment connections case 4. Component/action m-Factors IO

Yield of end plate Yield of bolts Failure of weld

2 1.5 1.25

Primary

Secondary

LS

CP

LS

CP

5.5 2 1.5

7 3 2

7 4 3

7 4 3

Table 3.3.15 Acceptance criteria for linear procedures (PR) moment connections case 5. Component/action m-Factors IO

Failure of deck reinforcement Local flange yielding and web crippling of column Yield of bottom flange angle Tensile yield of rivets or bolts at column flange Shear yield of beam flange connections

Primary

Secondary

LS

CP

LS

CP

1.25 1.5

2 4

3 6

4 5

6 7

1.5 1.25

4 1.5

6 2.5

6 2.5

7 3.5

1.25

2.5

3.5

3.5

4.5

Case 2: partially restrained moment connection with double split tee method (Table 3.3.17). Case 3: partially restrained moment connection with bolted flange plate method (Table 3.3.18). Case 4: partially restrained moment connection with bolted end plate method (Table 3.3.19).

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Table 3.3.16 Acceptance criteria for nonlinear procedures (PR) moment connections case 1. Component/ Modeling parameters Acceptance criteria action Plastic rotation angle (radians) Residual Plastic strength rotation IO Primary Secondary ratio angle (radians) a

Shear failure of rivet or bolt (limit state 1) Tension failure of horizontal leg of angle (limit state 2) Tension failure of rivet or bolt (limit state 3) Flexural failure of angle (limit state 4)

b

c

LS

CP

LS

CP

0.036 0.048 0.200

0.008 0.020 0.030 0.030 0.040

0.012 0.018 0.800

0.003 0.008 0.010 0.010 0.015

0.016 0.025 1.000

0.005 0.008 0.013 0.020 0.020

0.042 0.084 0.200

0.010 0.025 0.035 0.035 0.070

Table 3.3.17 Acceptance criteria for nonlinear procedures (PR) moment connections case 2. Component/action Modeling parameters Acceptance criteria

Shear failure of rivet or bolt (limit state 1) Tension failure of rivet or bolt (limit state 2) Tension failure of split tee stem (limit state 3) Flexural failure of split tee (limit state 4)

Plastic rotation angle (radians)

Residual strength ratio

a

c

b

Plastic rotation angle (radians) IO

Primary

Secondary

LS

LS

CP

CP

0.036 0.048 0.200

0.008 0.020 0.030 0.030 0.040

0.016 0.024 0.800

0.005 0.008 0.013 0.020 0.020

0.012 0.018 0.800

0.003 0.008 0.010 0.010 0.015

0.042 0.084 0.200

0.010 0.025 0.035 0.035 0.070

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Seismic Rehabilitation Methods for Existing Buildings

Table 3.3.18 Acceptance criteria for nonlinear procedures (PR) moment connections case 3. Component/action Modeling parameters Acceptance criteria Plastic rotation angle (radians)

Residual Plastic rotation angle (radians) strength IO Primary Secondary ratio

a

c

b

Failure in net section 0.030 0.030 0.800 of flange plate or shear failure of bolts or rivets Weld failure or 0.012 0.018 0.800 tension failure on gross section of plate

LS

CP

LS

CP

0.008 0.020 0.025 0.020 0.025

0.003 0.008 0.010 0.010 0.015

Table 3.3.19 Acceptance criteria for nonlinear procedures (PR) moment connections case 4. Component/ Modeling parameters Acceptance criteria action Residual Plastic rotation angle (radians) Plastic strength rotation IO Primary Secondary ratio angle (radians) a

b

c

Yield of end plate 0.042 0.042 0.800 Yield of bolts 0.018 0.024 0.800 Failure of weld 0.012 0.018 0.800

LS

CP

LS

CP

0.010 0.028 0.035 0.035 0.035 0.008 0.010 0.015 0.020 0.020 0.003 0.008 0.010 0.015 0.015

Case 5: partially restrained moment connection with composite methods (Table 3.3.20).

3.3.4.4 Brace frame A braced frame is a structural system commonly used in structures subject to lateral loads such as wind and seismic pressure. The members in a braced frame are generally made of structural steel, which can work effectively both in tension and compression. The beams and columns that

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Table 3.3.20 Acceptance criteria for nonlinear procedures (PR) moment connections case 5. Component/action Modeling parameters Acceptance criteria

Failure of deck reinforcement Local flange yielding and web crippling of column Yield of bottom flange angle Tensile yield of rivets or bolts at column flange Shear yield of beam flange connections

Plastic rotation angle (radians)

Residual strength ratio

a

c

b

Plastic rotation angle (radians) IO

Primary

Secondary

LS

LS

CP

CP

0.018 0.035 0.800

0.005 0.010 0.015 0.020 0.030

0.036 0.042 0.400

0.008 0.020 0.030 0.025 0.035

0.036 0.042 0.200

0.008 0.020 0.030 0.025 0.035

0.015 0.022 0.800

0.005 0.008 0.013 0.013 0.018

0.022 0.027 0.200

0.005 0.013 0.018 0.018 0.023

Figure 3.3.34 Complex brace frame and moment frame structure.

form the frame carry vertical loads, and the bracing system carries the lateral loads. The positioning of braces, however, can be problematic as they can interfere with the design of the façade and the position of openings. Buildings adopting high-tech or postmodernist styles have responded to this by expressing bracing as an internal or external design feature [1,2] (Fig. 3.3.34).

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3.3.4.4.1 Bracing systems 3.3.4.4.1.1 Vertical bracing

Bracing between column lines (in vertical planes) provides load paths for the transference of horizontal forces to ground level. Framed buildings require at least three planes of vertical bracing to brace both directions in plan and to resist torsion about a vertical axis. 3.3.4.4.1.2 Horizontal bracing

The bracing at each floor (in horizontal planes) provides load paths for the transference of horizontal forces to the planes of vertical bracing. Horizontal bracing is needed at each floor level, however, the floor system itself may provide sufficient resistance. Roofs may require bracing. 3.3.4.4.2 Linear analysis method (static and dynamic) for CBF brace 3.3.4.4.2.1 Steel concentric braced frame—CBF brace

Frames that the earthquake force is depreciated by the concentric bracing are called CBF. In which the seismic load capacity is evaluated in terms of the axial force capacity tolerated by the braces. Bracketed frames with axes (CBF) are bracketed frame systems in which the member axes are connected each at one point, unless the distance between the farthest intersection point of the intersection of the beam and column axes to the cross-section are smaller than or equal to the smallest member connecting at the intersection point. 3.3.4.4.2.1.1 Determining of stiffness of components for CBF brace frame The stiffness determination is performed in linear analysis as described in the stiffness modeling of FR moment frame and PR moment frame. Also to derive more realistic results, it is advisable to consider the stiffness of the panel zone in the model. Braces shall be modeled as columns [1,2]. 3.3.4.4.2.1.2 Determination of strength of CBF brace Determining the strength of these components includes the following. 3.3.4.4.2.1.2.1 Expected compression strength of CBF brace

1. The expected compression strength in the brace must be one of the two minimum values corresponding to the local buckling or the overall buckling of the member. The effective design strength, PCE, shall be calculated in accordance with AISC (1993) LRFD Specifications, taking ϕ 5 1.0 and using the expected yield strength Fye for yield strength.

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1. In CBF brace the effective length of each bracing member in the frame in-plane behavior is 0.5 for length inboard plane and 0.7 for the outboard. 2. In CHEVRON braces, the buckle length of the bracket is equal to the length of the off-plate and is 0.8 for length. 3.3.4.4.2.1.2.2 Expected tensile strength for brace for CBF brace The expected tensile strength QCE of steel bracing should be calculated similar to the behavior of the tensile columns (Fig. 3.3.35). 3.3.4.4.3 Linear analysis method for eccentric braced frames (EBF) (static and dynamic) 3.3.4.4.3.1 Steel eccentric braced frames (EBF):

Brace frames that have a distance between the intersections points of the brace greater than the cross section of the smallest member connected at these points are called EBF. The member between the brace intersection points is called the e-beam (Fig. 3.3.36).

Figure 3.3.35 Types of concentric braces frame.

Figure 3.3.36 Steel eccentric braced frames—EBF brace.

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Seismic Rehabilitation Methods for Existing Buildings

3.3.4.4.3.2 Determining stiffness of components for EBF brace frame

The elastic stiffness of the beams, brace, and their connections is determined by the criteria provided in moment frames and concentric braced frames. The elastic stiffness of the bond beam is determined using the following equations. The behavioral model of a transverse beam involves flexural and shear deformation [1,2] (Fig. 3.3.37). 3.3.4.4.3.3 Determination of strength of components

1. Calculate the lower boundary of compressive strength, PCL of EBF components such as columns, which is the flow resistance as the flow resistance FyLB at the lower boundary. 2. Calculate the expected resistance QCE and its lower bound QCL for beams and columns in accordance with the criteria given in FR moment frames. 3. The strength of the E-Beam depends on the length of the E-beam calculated by shear, flexural or a combination of the two case. Intermediate values are obtained by linear interpolation [1,2] (Fig. 3.3.38).

Figure 3.3.37 Chart of stiffness evaluation for eccentric braced frames.

Figure 3.3.38 Chart of strength evaluation for eccentric braced frames.

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3.3.4.4.4 Acceptance criteria for CBF brace and EBF brace CBF brace: 1. Tension and pressure in the braces are controlled by deformation. 2. The behavior of beams and columns in frame with concentric brace are force controlled. 3. The effects of pressure, tensile, shear, and bending on the brace connection components including plates, bolts, welds, and other components of connection shall be force-controlled. 4. Coefficients m for steel members shall be extracted from the tables in acceptance criteria linear analysis methods. EBF brace: 1. Shear and flexural in the beam should be considered as controlled by deformation. 2. In all other cases, and in the case of other members of the EBF, all conduct shall be force-controlled. 3. The compressive, tensile, shear and bending efforts of the joints of the braces, which include plates, bolts, welds, or other components, shall be considered force-controlled. 4. For details of transplant beams, the rules and principles of the bylaws should be made. 5. The resistance of the beam bracket and column to be bonded shall be 25% greater than the resistance such as the beam to prevent the yielding beam from flowing without buckling of the beam and column. 6. Where the bonding beam is attached to the flange of the column by full penetration welding, the requirements of these shall be the same as those relating to full penetration welding in flexural frames (Fig. 3.3.39 and Tables 3.3.21 and 3.3.22).

Figure 3.3.39 Concentric braced frame—chevron brace deformation on seismic load.

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Seismic Rehabilitation Methods for Existing Buildings

3.3.4.4.5 Nonlinear (static and dynamic) analysis and evaluation method for CBF brace 3.3.4.4.5.1 Determining stiffness of components for CBF brace

In nonlinear analysis the behavior in nonelastic range is evaluated and defined using the deformation and force historic diagram.

Table 3.3.21 Accept criteria in linear methods of m-factor for brace frame. Component/action m-Factors IO

Primary

Secondary

LS

CP

LS

CP

6 5 6 6 5 5

8 7 8 8 7 7

7 6 6 7 6 5

9 8 8 9 8 7

Braces in compression(expected EBF brace)

Double angles buckling in-plane Double angles buckling out-of-plane W or I shape Double channels buckling in-plane Double channels buckling out-of-plane Concrete-filled tubes

1.25 1.25 1.25 1.25 1.25 1.25

Rectangular cold-formed tubes

pffiffiffiffiffi ðd=tÞ # ð90= F 0y Þ pffiffiffiffiffi ðd=tÞ $ ð190= Fy Þ pffiffiffiffiffi pffiffiffiffiffi ð90= Fy Þ # ðd=tÞ # ð190= Fy Þ

1.25 5 7 5 7 1.25 2 3 2 3 Linear interpolation shall be used

Circular hollow tubes

ðd=tÞ # ð1500=Fy Þ ðd=tÞ $ ð6000=Fy Þ ð1500=Fy Þ # ðd=tÞ # ð6000=Fy Þ Braces in tension (except EBF braces) Beams, columns in tension (except EBF beams, columns)

1.25 5 7 5 7 1.25 2 3 2 3 Linear interpolation shall be used 1.25 6 8 8 10 1.25 3 5 6 7

Table 3.3.22 Accept criteria in linear methods of m-factor for EBF link beam. Component/action m-Factors IO

Primary LS

Secondary CP

LS

CP

EBF link beam

e # ð1:6MCE =VCE Þ 1.5 9 13 13 Linear interpolation shall be used e $ ð2:6MCE =VCE Þ Linear interpolation shall be used ð1:6MCE =VCE Þ , e , ð2:6MCE =VCE Þ For tension-only bracing, m-factors shall be divided by 2.0

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Types of existing buildings: detailed introduction and seismic rehabilitation

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3.3.4.4.5.2 Determination of strength of components for CBF brace

Nonlinear static method The expected strength values of QCE are the same as those for the linear methods. Nonlinear dynamic method In this method, the complete cyclic behavior of each bracing member should be evaluated and tested. 3.3.4.4.5.3 Determination of stiffness of components for EBF brace

Instead of using test or analysis based relationships, model the nonlinear force
displacement behavior of each member in EBF using extracted force and displacement curves. 1. Nonlinear models for beams, columns, and connections are made in moment frames. 2. Rotation angle of the link beam (e-beam) at the yielding point must be determined through following equation: Ke is the elasticity stiffness of the link beam that can be determined based on the rules.θy 5 QCE =Ke e If nonlinear dynamic method is used, full cyclonic behavior of each member—that is based on a test or a valid analytic method, must be modeled. 3.3.4.4.5.4 Determining the strength of components

Nonlinear static procedure It is done in accordance with the provided rules about eccentric braced frames (EBF) in the determining linear strength section. Nonlinear dynamic procedure In this method full cyclonic behavior of each member is modeled based on a test or a valid analytic method. 3.3.4.4.5.5 Acceptance criteria for nonlinear procedure for CBF and EBF brace

Computational efforts of the members must meet the criteria presented in the chapter of analytical methods. The amount of deformation is determined through Table 3.3.23 (Fig. 3.3.40).

3.3.4.5 Steel plates shear wall Steel shear walls are steel plates surrounded by beams and columns. In this frame beams and columns are called boundary elements (Fig. 3.3.41).

Table 3.3.23 Accept criteria in nonlinear methods of brace. Component/action

EBF link beam e # ð1:6MCE =VCE Þ e $ ð2:6MCE =VCE Þ ð1:6MCE =VCE Þ , e , ð2:6MCE =VCE Þ Braces in compression (except EBF braces) Double angles buckling in-plane Double angles buckling out-of-plane W or I shape Double channels buckling in-plane Double channels buckling out-of-plane Concrete-filled tubes Rectangular cold-formed tubes pffiffiffiffiffi .ðd=tÞ # ð90= pFffiffiffiffi0yffiÞ ðd=tÞ $ ð190= Fy Þ pffiffiffiffiffi pffiffiffiffiffi ð90= Fy Þ # ðd=tÞdð190= Fy Þ Circular hollow tubes

Modeling parameters

Acceptance criteria

Plastic rotation angle (radians)

Residual Plastic rotation angle (radians) strength ratio IO Primary Secondary

a

c

b

LS

CP

0.11

0.14 0.14

0.16

5ΔC 4ΔC 5ΔC 5ΔC 4ΔC 4ΔC

7ΔC 6ΔC 7ΔC 7ΔC 6ΔC 6ΔC

7ΔC 6ΔC 7ΔC 7ΔC 6ΔC 6ΔC

8ΔC 7ΔC 8ΔC 8ΔC 7ΔC 7ΔC

0.5ΔC 7ΔC 0.4 0.25ΔC 4ΔC 6ΔC 6ΔC 0.5ΔC 3ΔC 0.2 0.25ΔC 1ΔC 2ΔC 2ΔC Linear interpolation shall be used

7ΔC 3ΔC

0.15 0.17 0.8 0.005 Same as for beams Linear interpolation shall be used 0.5ΔC 0.5ΔC 0.5ΔC 0.5ΔC 0.5ΔC 0.5ΔC

9ΔC 8ΔC 9ΔC 8ΔC 8ΔC 7ΔC

0.2 0.2 0.2 0.2 0.2 0.2

0.25ΔC 0.25ΔC 0.25ΔC 0.25ΔC 0.25ΔC 0.25ΔC

LS

CP

ðd=tÞ # ð1500=Fy Þ ðd=tÞ $ ð6000=Fy Þ ð1500=Fy Þ # ðd=tÞ # ð6000=Fy Þ Braces in tension (except EBF braces) Beams, columns in tension (except EBF beams, columns)

0.5ΔC 0.5ΔC

9ΔC 3ΔC

0.4 0.2

11ΔT 5ΔT

14ΔT 0.8 7ΔT 1.0

0.25ΔC 4ΔC 6ΔC 5ΔC 0.25ΔC 1ΔC 2ΔC 2ΔC

8ΔC 3ΔC

0.25ΔT 7ΔT 9ΔT 11ΔT 13ΔT 0.25ΔT 3ΔT 5ΔT 6ΔT 7ΔT

ΔT is the axial deformation at expected tensile yielding load and ΔC is the axial deformation at expected buckling load.

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Seismic Rehabilitation Methods for Existing Buildings

The steel shear walls are similar to the girder, in which the columns have the function of girder flange, and the beams are as stiffener and plate of steel shear wall as girder web. Shear walls are divided into two types of stiffened and non- stiffened. If the shear wall is stiffened, the wall plate shall meet one of the following conditions:[3,5] Condition one: if used stiffeners in both horizontal and vertical directions S 650 # pffiffiffiffiffiffi tw Fye

(3.3.13)

Condition two: if the stiffeners is used in only one direction S 490 # pffiffiffiffiffiffi tw Fye

(3.3.14)

3.3.4.5.1 Calculation stiffness for shear wall The use of finite element method in plate stress state with beams and columns as edge elements is permitted for the analysis of steel shear walls. Linear method The stiffness of the steel shear wall is calculated from the following equation by considering its numerical parameters including the shear modulus. KW 5

Ga tw h

(3.3.15)

Nonlinear method This process is similar to other steel components previously described to calculate nonlinear stiffness. 3.3.4.5.2 Strength of steel shear wall Linear method For calculation strength of shear wall plate we can using two condition. This depends on the distance between the stiffeners. Condition one: depending on the ratio of a=tw , the shear wall can be modeled as a girder web, and finally calculated according to the rules of AISC 1997

Types of existing buildings: detailed introduction and seismic rehabilitation

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Condition two: if the distance between stiffeners is suitable for shear wall. We can calculated expected strength with by Equation. The resistance of other components, such as stiffeners, is calculated from the criteria AISC 1997. QCE 5 VCE 5 0:6Fye atw

(3.3.16)

Figure 3.3.40 Acceptance criteria for nonlinear static and dynamic procedure diagram.

Figure 3.3.41 Steel shear wall.

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Seismic Rehabilitation Methods for Existing Buildings

Nonlinear method It is important to calculate the yield deformation gear to determine the strength of the steel shear wall for nonlinear conditions. This parameter is extracted from the following equation. Eventually the same terms and conditions will continue like other components. Δy 5

QCE KW

(3.3.17)

3.3.4.5.3 Acceptance criteria In linear method blow condition must be considerate. 1. The shear behavior in the stiffened steel shear wall is assumed to be the deformation of the control and the m values are extracted from the following table. 2. The wall plate joints to the edge components shall be considered as members of the control force (Fig. 3.3.42 and Table 3.3.24). Nonlinear method for seismic rehabilitation steel shear wall The computational effort of the members for nonlinear behavior and its acceptance criteria for use in the load
deformation curve is extracted from Table 3.3.25.

Figure 3.3.42 Steel shear wall deformation. Table 3.3.24 Accept criteria in linear methods of steel plate shear walls. Component/action m-Factors IO

Steel plate shear walls

1.5

Primary

Secondary

LS

CP

LS

CP

8

12

12

14

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Types of existing buildings: detailed introduction and seismic rehabilitation

Table 3.3.25 Accept criteria in nonlinear methods of steel plate shear walls. Component/action Modeling parameters Acceptance criteria

Steel plate shear walls

Plastic rotation angle (radians)

Residual strength ratio

a

b

c

14θy

16θy

0.7

Plastic rotation angle (radians) IO

0.5θy

Primary

Secondary

LS

CP

LS

CP

10θy

13θy

13θy

15θy

3.3.5 Common seismic rehabilitation techniques 3.3.5.1 Methods for seismic rehabilitation of structural steelwork frame buildings In steel structures, usually beams are known as flexural members in frame. As in flexural issues a part of section is compression section, so that there is a risk of buckling in this area. There are two types of buckling for the area. In first one, flange or web of the section buckles separately and locally and in latter case, the overall buckling may occur for the compression part of section. Two factors determining the geometrical properties of the cross-section and the supports intervals or lateral bracings play a major role in preventing the two abovementioned buckling states [2,6,7]. In the design of flexural members, if the dimensions of the profile are such that the ratio of the width to the thickness of its components is less than those specified in the design codes and does not satisfy the compact section requirements, the flange or web of the section becomes locally unstable, buckles, and loses its bearing capacity. Also if the beam length exceeds a certain distance between the two lateral supports or in other words lacks the lateral support at appropriate intervals, before the maximum bending stresses in the beam reaches the yield limits, the compression flange of the beam is unstable and destroyed. Such destruction which is suddenly caused by increase in compression stress on the flange due to bending of the beam on one side and lateral bending of the beam due to its nonlateral holding and rotation of the beam that is a combination of pure torsion and distortion is known as the lateral-torsional buckling of the beam (Fig. 3.3.43).

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Seismic Rehabilitation Methods for Existing Buildings

Figure 3.3.43 Adding cover plate to column flange for seismic rehabilitation.

At the design stage of flexural member, the aforementioned cases and all the building codes are considered by the structural engineers and the final section is securely designed to minimize the possibility of lateraltorsional buckling of the beam. However, some issues might happen in the process of operation of the structure that endanger adequacy of the section. Among these issues we can name failures and deficiencies in implementation of the member, change in structure usage, structural damage due to natural disasters and applying forces greater that predicted loads. In such cases, one of the options for designers to consider is seismic rehabilitation the existing member. 3.3.5.1.1 Introduce some seismic rehabilitation methods for steel sections Rehabilitation of connections and components using suitable stiffeners and plates As it was discussed in previous section, due to lack of knowledge of connections’ behavior, most of the structural damages are due to failure in design or implementation of the connections. Thus it is necessary to investigate the damages caused to the connections due to the existing happened earthquakes properties. Connections damages caused by previous earthquakes can be classified as damages to beams, columns, welds, panel zone and other components. Widespread observation of such damages at connections due to past earthquakes is very alarming. In designing the connections, it must be taken into account that the connection must be capable of bearing the maximum tolerable force of the member. Failure to do so requires rehabilitation connections for seismic

Types of existing buildings: detailed introduction and seismic rehabilitation

487

rehabilitation. In steel structures, esp. restrained frame, connections are one of the most important parts of the structure. 3.3.5.1.1.1 Seismic rehabilitation methods of column and beam

•

•

•

Procedure of adding cover plate to column flange for seismic rehabilitation of steel column In seismic rehabilitation of steel construction, one of the ways of seismic rehabilitation of steel column is to add cover plate to column flange. In this method, which is shown below, local buckling of column flange is prevented by flange thickening (Fig. 3.3.44). Procedure of adding a plate parallel to the column web for turning section to a box shape Adding a plate parallel to the column web and turning it to a box section leads to seismic rehabilitation of steel column. As it shown in the figure, adding a plate parallel to column web leads to increase in inertial moment along the column web (Fig. 3.3.45). Procedure of Enclosing the steel section member by a concrete jacket (cover) Concrete jacket can be used in existing structural steelwork frame buildings that require seismic rehabilitation of the members and increased ductility. Using concrete jacket in columns leads to an increase in stiffness and strength of steel column, as well as an increase in strength of the member against buckling. The use of concrete jacket in the beams increases the moment and shear capacity of the beams. It

Figure 3.3.44 Adding cover plate to column flange for seismic rehabilitation.

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Seismic Rehabilitation Methods for Existing Buildings

Figure 3.3.45 Adding two plate parallel to the existing column web for seismic rehabilitation.

Figure 3.3.46 Two samples of using concrete jacketing the steel column for seismic rehabilitation.

•

•

should be noted that if a concrete jacket is to be used in the beams, careful consideration should be given to the weak beam-strong column criteria. Procedure of Using concrete jacket for steel column This method is used for seismic rehabilitation of steel open sections like “I” and “H.” Enclosing steel column increases its stiffness which leads to increase in shear stiffness too. To increase flexural stiffness of the column, concrete coating of the steel column must be continuous in different floors (Fig. 3.3.46). Rehabilitation of the corroded steel column using a concrete jacket is recommended as an effective solution. Seismic rehabilitation with this method will also have good strength against fire. Procedure of using Concrete material for filling the steel tube section to upgrade its performance level This method is used for steel box sections. An example of Concrete filled steel tube is shown in the figure (Fig. 3.3.47).

Types of existing buildings: detailed introduction and seismic rehabilitation

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Figure 3.3.47 Samples of seismic rehabilitation the steel tube sections by filling with concrete.

Figure 3.3.48 Frame seismic rehabilitation sample for beam and column with concrete covering.

•

Frame seismic rehabilitation sample for beam and column with concrete covering An example of a retrofitting scheme for seismic rehabilitation of beam and column in structures is provided below for a better understanding of the above concepts (Fig. 3.3.48).

3.3.5.1.1.2 Seismic rehabilitation methods of steel connection

Due to insufficient understanding of the behavior of the connections, many of the damages caused to the structures are due to weaknesses in the design or implementation of the connections. Therefore it is necessary to investigate damages caused by past earthquakes and provide appropriate rehabilitation solutions. Damages to steel connections caused by past earthquakes can be classified as damages to beams, columns, welds, components and panel zone. Damage to the connection may be one or more of the above or several types. The extensive observation of such damage at connections due to past earthquakes is very alarming.

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Seismic Rehabilitation Methods for Existing Buildings

3.3.5.1.1.3 Damage to connection in steel structures

To retrofit the building, it is necessary to first classify the types of damages and damages to the connection during the earthquake. Most of these failures are classified as follows: • Damage to beams (D.B) • Damage to column flanges (D.C) • Damage to Welding (D.W) • Damage to shear web plate (D.S) • Damage to panel zone (D.P) 3.3.5.1.1.3.1 Damage to the beams In the beam crashes in the Northridge earthquake, most of the damage was observed in the lower flange, although there were also reports of damage to the upper flange. This fact can be justified for several reasons as follows. 1. Complex performance of the concrete slab with the upper flange which results in the transfer of neutral fiber upwards and the stress in the lower flange. 2. Low quality butt welding of the lower flange to the column due to incomplete welder access to it during welding. 3. Ultrasound testing on the upper flange is easily possible, thereby enhancing the quality of its reception. 4. The welding strap on the lower flange is at maximum tension, while at the upper flange it is not at maximum tension. The existence of a strap behind the strap is the focus of stress. Eight types of damage to the beam are likely to occur (Fig. 3.3.49 and Table 3.3.26).

Figure 3.3.49 Eight types of damage to the steel beam.

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Table 3.3.26 Types of breakdowns in steel beams.

D.B1 D.B2 D.B3 D.B4 D.B5 D.B6 D.B7 D.B8

Buckling flanges (upper or lower flange) Flange yielding (upper or lower flange) Collapse flange in weld area(upper or lower flange) Collapse flange in outer of weld area(upper or lower flange) Upper or lower flange collapse Yielding with buckling web Web collapse Lateral buckling of beam lower flange

Figure 3.3.50 Types of breakdowns in steel column.

3.3.5.1.1.3.2 Damage of columns The occurrence of seven types of damage to the column flange is likely as shown (Fig. 3.3.50 and Table 3.3.27). 3.3.5.1.1.3.3 Disadvantages and defects of welding The seven types of failure, defect and discontinuity of welding are shown in Fig. 3.3.51 (Table 3.3.28). 3.3.5.1.1.3.4 Damage to the shear coupling plate of beam web Ten types of breakdown shear coupling plates are shown in the figure. The major failure occurring in shear connection plates is the occurrence of failure in columns, beams, welds or panel zone (Fig. 3.3.52 and Table 3.3.29).

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Table 3.3.27 Types of breakdowns in steel column.

D.C.1 D.C.2 D.C.3

Limited cracks Flanges spalling Complete or limited cracks out of welding area Complete or limited cracks in boundary welding area Layer spalling Column flange buckling Splice collapse

D.C.4 D.C.5 D.C.6 D.C.7

Figure 3.3.51 Types of failures and defects of welding.

Table 3.3.28 Types of failures and defects of welding.

D.W.1 D.W.2 D.W.3 D.W.4 D.W.5 D.W.6 D.W.7

Cracks in the weld root D.W.1 1 Cracks to a depth of less than 5 mm or tf =4 and width less than bf =4 D.W.1 1 Cracks deeper and larger than W1a Crack in full thickness weld metal Collapse in the joint of weld metal with column collapse in the joint of weld metal with beam Symptoms detectable with UT-nonrejection test

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Figure 3.3.52 Types of breakdowns in shear coupling plates.

Table 3.3.29 Types of breakdowns in shear coupling plates.

D.S.1 D.S.2 D.S.3 D.S.4 D.S.5 D.S.6 D.S.7 D.S.8 D.S.9 D.S.10

Partial crack in welding plate to column D.S.1 1 Healthy beam flanges D.S.1 1 flanges cracked Collapse in extended welding D.S.4 1 Healthy beam flanges D.S.4 1 flanges cracked Crack in bolt boundary area Yielding or buckling of shear web plate Loose, damaged or forgotten Bolts Complete breakdown of weld shear plate to column

3.3.5.1.1.3.5 Damage to panel zone Nine types of failures at the panel zone are shown in Fig. 3.3.53 (Table 3.3.30). 3.3.5.1.1.3.5.1 Connection failures Due to the damages caused to the connection by previous earthquakes, the connection failures can be classified as follows: 1. Lack of choosing the right details (wrong connection structure) 2. Incompatibility in connecting plates 3. Not paying attention to the free and slim edges of the connecting plates 4. Incorrect spacing of connectors 5. Ignoring access to blind connection points 6. Inaccuracies in welding with the correct length and dimension

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Figure 3.3.53 Nine types of breakdown damage to the Panel zone in steel structure. Table 3.3.30 Types of breakdowns in panel zone.

D.P.1 D.P.2 D.P.3 D.P.4 D.P.5 D.P.6 D.P.7 D.P.8 D.P.9

Collapse, buckling in continuity plates collapse in welding of continuous plates Yielding or deformation of web section Double weld break failure Minor collapse in double plates Minor collapse in column web Complete collapse in column web or double plate Web buckling Column completed collapse

3.3.5.1.1.4 Seismic rehabilitation of connections against damage

3.3.5.1.1.4.1 Continuity Plates The attachment plates shall be positioned against the beam flanges or the cover plates of the upper and lower joints of the beams attached to the column and symmetrically relative to the column axis. These plates are used to transfer in-plane forces from the moment of beam to the panel zone in the column (Fig. 3.3.54). The shear strength of the panel zone and other design panel zone criteria are determined in each design method according to the design criteria of the steel structure. If the panel zone cannot restrained the shear induced by the tensile and compressive forces on the flanges of the column beams, the panel zone reinforcement plates should be used to reduce shear stress in the column life or to prevent its instability. These plates can be attached to the column die or spaced symmetrically to the axis of symmetry of the column cross-section which is parallel to the shear force applied. These plates should be attached to the column flanges and the upper and lower continuity plates. Panel zone of the upper and lower edges of

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the panel zone reinforcement plates for joining plates and welding of the vertical edges of these plates to the column flanges shall be designed for the portion of the shear end shear tolerated by them. The panel zone reinforcement plates can be run as in Fig. 3.3.55. 3.3.5.1.1.4.2 Welding steel connections reinforcement solution After examining common damages in welded connections and providing important criteria for designing panel zone reinforcement plates and continuity plates and how to calculate the forces at critical connections, we introduce the methods of retrofitting common welds. Use double upper and lower plates If the plates are not welded to the column or damaged during an earthquake, the use of double upper and lower plates for retrofitting like Fig. 3.3.56. If there is no confidence in the welding of the existing plates to the column or if the weld is missing, the thickness for new plates should be designed for the plastic moment of beam. But if adding plates to reinforce existing metal connections, the thickness is determined by judgment.

Figure 3.3.54 Implementation of continuity plates.

Figure 3.3.55 How to welding new plates for seismic rehabilitation the continuity plates zone.

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Use diagonal plate-like hunched connection for retrofitting The following figure shows the details of adding diagonal plate. Adding this plates will transfer the plastic joint from the column to the beam. Adding plates if possible should only be done on the lower flange because the experience of the earthquake indicates the onset of damage from the lower flange of beam, as well as adding the plate on the upper flange will require damage to the slab. Adding plate at the bottom is feasible if the building has a false ceiling and eliminates the need to repair welded plates to the column. If we are not sure about welding the plate to the column and do not want to sub it and repair it, we can also apply the plate above. In this case, there is a possibility of diagonal interference with flooring. If there is no confidence in the welding of the existing plates to the column or if the weld is missing, the thickness of the upper and lower plate should be designed for the plastic moment of beam. But if adding plate to retrofitting existing steel connection, the thickness is determined by judgment (Fig. 3.3.57).

Figure 3.3.56 Double upper and lower plates for retrofitting.

Figure 3.3.57 Samples of the welding of diagonal plates in the upper and lower of a plastic hinge place for seismic rehabilitation.

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Figure 3.3.58 Retrofitting connections with gusset plate.

Figure 3.3.59 Two sample of using side plates for seismic rehabilitation of connections.

Using vertical gusset plate in upper and lower flanges Fig. 3.3.58 shows how to retrofitting rigid steel connection with vertical gusset plates. The number of gussets can be one or two. Use side plates (species plates) In this method, the tensile and compressive forces of the upper and lower flanges of the beam are transferred to the column by the cheek plates. Examples of details of retrofitting of steel plate side connections are shown in the figure (Fig. 3.3.59). Use T-shaped cross section T-shaped sections can be retrofitting steel connection. In some cases, the cross-section is performed only at the lower flange of the connection, which can be reinforced without damaging the slab. Attachment plates should also be run along the T-shaped sections (Fig. 3.3.60). 3.3.5.1.1.4.3 Retrofitting of steel beams with external tension by tensile cable Applying retrofitting with external pretensioning is one of the most recent methods of steel reinforcement improvement developed

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Figure 3.3.60 Retrofitting with T-section.

in recent years. High-strength cable is usually mounted in the middle of the beam. This method can also be performed with four cables. The good thing about using four cables is that by not losing a single cable, the connection function will not be interrupted. The shear strength of the joint is provided by two poles at the top and bottom and the frictional force between the beam and the column, which is also increased due to cable preload. Separating the beam from the column leads to energy absorption because the beam is pulled from the column and the nonlinear function of the cables results in energy absorption. Using this method leads to increased strength, stiffness and ductility of the connection. There are some problems with using this method, such as cable surrender and beam buckling. The benefits of this method can be: • Nonlinear functional integration of structural components resulting in limited seismic forces and providing additional damping for the structure • Return to the original state after seismic load deformations • Reducing or eliminating severe damage to the main structural elements (Fig. 3.3.61). 3.3.5.1.1.4.4 Retrofitting solutions fully restrained moment connection with bolt or weld This section contains the necessary recommendations for all types of fully restrained moment connection such as a pervious methods. 3.3.5.1.1.4.5 Increase the length of the end plate and the use of a hardener in attaching the bolt connection to the end plate In this connection the end plate is connected to the beam by welding so that the

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Figure 3.3.61 Retrofitting with T-section.

flanges of the beam are connected to the end plate by the welding of the penetrating groove and the die beam by the corner welding. Finally the end plate is attached to the column with bolts. Welding the beam flanges to the end plate without access holes. The lower end of the plate is hardened by generic softeners rather than beam flanges. These hardeners are attached to the beam flange and end plate by means of a two-way penetration groove. This connection can be used in ordinary moment frames and special moment frames with respect to member size. In this method, the flexural strength of the connection can be increased by increasing the length of the end plate by welding the plate added to the existing end plate and reinforcing the additional end plate to the column flange. 3.3.5.1.1.4.6 Seismic rehabilitation of base plate As we see in the seismic rehabilitation quantitative evaluation studies of steel columns, the column base plate is not sufficient cross section. We must first design the expected capacity and then perform the retrofitting operations using the following sequence. • First, clean the side of the base plate. • The second stage is fitting the bolts designed to the expected strength. • The third step is cutting steel plates for retrofitting. • Step four Install steel plate into the bolts and then attach the new plates to the existing base plate (Fig. 3.3.62). 3.3.5.1.1.5 Seismic rehabilitation methods of steel skeleton building

3.3.5.1.1.5.1 Improving stiffness for building have a potential of soft story If it is found that the major weakness of the structure is due to its lack of lateral stiffness and as a result of the lots of displacements, it is possible to provide the required lateral stiffness by suitable solutions such as increasing bracing or shear walls. In this situation, the interaction

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Figure 3.3.62 Potential of soft story simulation.

between the present structure and the new load-resisting system must be studied carefully. If the braced frame or shear wall have great stiffness, it may absorb a significant portion of the side loads. If capacity increases by adding a new moment frame due to the softness of the frame, the interaction between the existing structure and the new moment frame causes the load to be distributed between the two systems. In this case, behavior of the brittle members of the structure due to displacements of the rehabilitated building must be studied carefully (Fig. 3.3.63). Adding braces to steel frames is an efficient method that can help with the seismic rehabilitation of a structural steelwork frame building if the building is of low stiffness or poor welding or poor details of connections. It is worth mentioning that if a brace is used to rehabilitation of this building, the columns are needed to be controlled in terms of their

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Figure 3.3.63 Potential of soft story simulation.

strength against local buckling. EBF braces are less commonly used in rehabilitation of existing buildings because of the weak strength of the beam designed solely for the gravity load, and its partial rehabilitation to be used as a link beam will be generally costly and difficult. Coaxial steel braces increase stiffness, limit rotation at the beam column connections, and respectively, reduce overall and relative displacements of the structure and floors. However, due to reduce in fundamental period of the structure, building must be controlled against greater values of earthquake force. It should be noted that in case of adding a brace or shear wall it is necessary to analyze the foundation of the building to be controlled against the imposed forces and uplifts. 3.3.5.1.1.5.2 Procedure of adding new braces to existing building The addition of a new steel brace is used to reinforce the steel structure to increase stiffness, reduce the need for ductility and increase shear strength. The using all types of bracing systems is usually used in the retrofitting of steel structures due to their low cost and low performance problems and low detailing, to improve overall structural performance (Fig. 3.3.64). 3.3.5.1.1.5.3 Procedure of retrofitting by adding new column to existing building Adding a column to the soft story leads to seismic rehabilitation in two ways caused: 1. increasing the stiffness of soft story and 2. reducing in loading section of beam that leads to increase in bearing capacity of the beam (Fig. 3.3.65).

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Figure 3.3.64 Samples of adding new steel brace to existing frame for Seismic Rehabilitation.

Figure 3.3.65 Adding new column and Frame for seismic rehabilitation.

3.3.5.1.1.5.4 Procedure of retrofitting by adding new shear wall with concrete or steel material to existing building In recent years, using shear wall in new buildings and so rehabilitation of existing buildings has grasped lots of attention. This system has proper stiffness to control structure deformation and also by satisfying the designing criteria, these walls have ductile disrupt mechanism with high values of energy loss. Due to their high strength, these walls are very economical to be used in high buildings, but for low- and medium height buildings, side issues such as retrofit of adjacent structural elements has a great impact on its executional and economic aspects. An example of the implementation details of the new shear wall is shown in Fig. 3.3.66.

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3.3.5.1.1.5.5 Procedure of adding new infill wall to existing frame in building same as hybrid wall system One of the methods of increasing the strength and lateral stiffness of structures is to add infill. Adding infill walls increases the stiffness and reduces the fundamental period of the structure by up to 20%, indicating the effect of the infill on the structural stiffness. This method is mostly used in short steel buildings. When an infill is used to provide stiffness, the interaction between structural elements and the infill must interact be examined. Depending on the materials used, the infills can be made of brick, concrete, etc. In the meanwhile, adding masonry infills as a method of increasing strength and lateral stiffness of the structure is never recommended. Because under seismic loads, the masonry infills only withstand the first loading cycles and greatly increase the weight of the structure. Concrete walls inside building frames can be armed or unarmed. Also shows in (Fig. 3.3.67) the function of creating a gap in the distribution of

Figure 3.3.66 Samples of adding new shear wall with concrete or steel material to existing frame for seismic rehabilitation.

Figure 3.3.67 The function of creating a gap in the distribution of lateral force to add a new infill wall.

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lateral force for the method of adding infill wall in existing frames in order to improve the seismicity of the existing building. 3.3.5.1.1.5.6 Executional procedure of compressive and tensile brace to cantilever When the length of cantilever is too long, due to the overload of the cantilever and the vertical component of the earthquake it is necessary to brace the cantilever. To do this, it is necessary to implement brackets on the top or bottom of the cantilever with respect to the force applied to it to prevent excessive deflection and double bending force on the column. 3.3.5.1.1.5.7 Executional procedure of a new beam between present columns In some cases, beams are unable to withstand the imposed load and cause excessive deflection. A good way for seismic rehabilitation of these beams is to use some beams between columns and in the middle of the span that cause the wall weight on the beams to be reduced by half. In this method of seismic rehabilitation, the connection of the added beam must be a hinge so as not to have any strength against lateral force. 3.3.5.1.1.5.8 Seismic rehabilitation method using fiber-reinforced polymer composites This is one of the methods of seismic rehabilitation that in recent years, is suggested as a modern and efficient method. Extraordinary physical and mechanical properties of fiber-reinforced polymer (FRP) composites alongside the various advantages are the main reasons for using them in seismic rehabilitation existing buildings and rectification. Having linear elastic behavior before fracture, high strength/ weight ratio, strength against environmental impacts, ease of implementation, unlimited access to different size, shape and dimensions as well as insulation are of the most important properties of FPR composites. In using FPR composites to rehabilitation of steel beams, the FPR composites are put on the cross section components of steel beam and lead to their bracing against local buckling. Depending on the type of member’s cross section, the support conditions, and the dimensional characteristics of the flange and web of cross section, different layouts for beam section can be selected. However, the thickness and dimensions of the FRP composite used to retrofit the beam can be selected to cover part of the cross-section or to be used to retrofit the entire cross-section depending on various factors such as computational conditions and economic considerations. Enhancement of lateral torsional buckling capacity and increase in critical buckling load are among the results of steel beam

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retrofit by FPR composites. In this way, the bearing capacity can be increased by delaying the lateral torsional buckling and reducing lateral displacements. 3.3.5.1.1.5.9 Seismic rehabilitation method using dampers According to recent earthquakes, seismic retrofitting is a new type of performance that includes a seismic system that operates only against various earthquake vibrations and has no role in bearing static loads. These methods prevented the building from shaking during the earthquake. The systems presented were based on separating the structure from the earthquake. By defining new members in a structure called Damper that cause seismic energy loss to the building and by applying them to the building, we can an optimized building which is capable of a suitable and desirable performance against dynamic bars resulted from earthquakes. In this method, since little or no earthquake force is not applied to the structure, the following the results can be expected: • decrease in floor drift and relative floor drift, • significant decrease in floor acceleration, • significant decrease in structural and nonstructural damages, • decrease in architectural problems during building design, and • decrease in execution cost due to using sections with less capacity. Knowing damping of a substance, we can have an accurate analysis of the systems consisting of that substance. Considering that inner damping (depending on material) changes in solids when subjected to factors such as temperature, fatigue phenomenon, and Bauschinger effect, to have materials with a determined damping, we must minimize the effects of these factors. There are several methods to produce materials with a determined damping, which are called damper. Common earthquakes often have time period in 0.10
1 seconds. Structures with time period between 0 and 1 are vulnerable against these earthquakes since resonance might occur in them. The most important feature of seismic separation is to create flexibility that helps to increase natural time period of the structure. Increasing natural time period decreases the probability of resonance occurrence and also decreases acceleration in the structure. This also affects horizontal displacements (drifts). Increasing time period and its effects on the highest values of drift in separated structure with low damping might reach strong earthquakes up to one meter. Damping can reduce this amount up to 50
400 mm. This amount of drift must be provided with seismic seam. Actual structural responses

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depend on different factors such as mass distribution and seismic separation parameters. Different types of passive dampers • friction damper, • viscoelastic damper, • viscous damper, • tuned mass damper, and • tuned liquid damper. These systems are generally subdivided into displacement, velocity, and other groups. Displacement-dependent devices must include devices that have hard-plastic behavior (such as frictional or bilinear behavior such as flowing metal devices). Speed-dependent devices include viscoelastic and viscous dampers. Energy-saving equipment that does not fall into these two categories is among the other. This section describes each of the above dampers and explains how they work. Displacement-dependent dampers are subdivided into two types of frictional and fractional dampers, which are more advantageous than fractional systems due to the relatively easy and inexpensive installation and replacement of frictional systems (Fig. 3.3.68). 3.3.5.1.1.5.10 Building retrofit by seismic separation using base isolation units Seismic separation is one of the methods of controlling seismic vibrations by separating structures from the ground in buildings and bridges. In this method, unlike conventional seismic retrofitting, which focuses on structural enhancement, it focuses on reducing seismic response, and the strength and acceleration of earthquake input to the structure. It should be noted that seismic separators include all dimensions

Figure 3.3.68 Seismic rehabilitation method by using dampers.

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Figure 3.3.69 The function of depreciating the lateral load in the existing building by adding base isolation.

of the building and cannot be used in part of their structure as this can cause displacement of two parts of the building. The periodicity of the structures in which the separator is used is estimated to be 2
5 seconds due to the use of these separators. Also in buildings with very poor soil or high-rise buildings and flexibility may not be possible, using a separator can be very beneficial. In seismic separation, the main periodicity of the structure is increased by means of equipment as shown below, between the surface and its downstream section. Therefore mechanisms for energy dissipation are incorporated in the separation system to reduce the acceleration of the structure while limiting displacement (Fig. 3.3.69). Therefore a separation system must have the following capabilities: • able to withstand the vertical forces caused by the earthquake response and weight during the earthquake; • provide the necessary flexibility in the horizontal direction; and • ability to absorb energy. These capabilities can be provided simultaneously on a single device or provided with a number of devices for separation. In addition, the designer may anticipate bumpers in the seismic separation system to limit the displacement of the separators. Two main groups of seismic separators are used to control the force transmitted to the pavement in buildings: • using rubber separators to increase the natural periodicity of the structure and • using friction separators and maximizing the force transmitted to the surface and energy dissipation at the separator site. The separators shall have the strength necessary to withstand the structural weight of the zinc itself.

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Types of seismic separators In general, seismic separators can be divided into two categories: rubber separators and friction separators. The following separators are rubber separators: • rubber separators with steel plates (and low attenuation), • highly attenuated rubber separators, and • lead-core rubber separators. Friction separators are mainly manufactured in the following industries: • friction separators, • friction elastic separators, and • pendula friction separators. To utilize the capabilities of rubber and friction separators at the same time, the two systems are combined: • composition of series of friction and rubber separators and • parallel combination of friction and rubber separators.

3.3.6 Two real case study example 3.3.6.1 Example of 10-story steel special moment frame building 1 center brace frame with SMD rigid diaphragm 3.3.6.1.1 Introduction This example includes a building with steel structure, which has been under construction since 2014 in one of the cities of Iran with a relatively high seismic hazard. The structure construction has already been terminated. The present building is located in an area of about 10763.9 ft.2 with an occupied area of 100% in the first two floors, and 60% in the top floors. It is a 10-storey building, which is initially considered to have a residential use. The building have 127.95 ft. length, 63 ft. width, and 95.14 ft. height from the street level. One should have it mind that the length of the building in the top floors is reduced to 104 ft. In the first design of the building, considering that the building has a residential use, the number of residents has been considered to be 100 person. The structure of this building is a steel structure with FRMF integrated with CBF braces based on the design and execution in north to south longitudinal directions (with geographical directions from north to south), and in the

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transversal direction (with geographical directions from east to west), it has a steel structure with PRMF. As you proceed, you will see that this building has several inconstancies of the structure due to lack of consistency among its frames. This is one of the most important problems in this building. There are very high cantilever beams which need to be analyzed in this building. At the first stage, the building has been designed for the basic performance level (to provide life security in BSE-1 earthquakes). However, according to its use to be a specialized medical (therapeutic) clinic, it has become highly important. Therefore it should be seismically rehabilitated and none-structural components should be evaluated constantly for BSE-2 earthquakes. What we will discuss in this example: 1. Getting to know structures which lack consistent structural system and require seismic rehabilitation. 2. Getting to know buildings which must be seismically rehabilitated using a proper method due to a change in the building use. 3. Getting to know seismic rehabilitation system in the structure of façade for high cantilever beams (Fig. 3.3.70). Seismic rehabilitation stages in this example are: • Primary qualities evaluation done in field inspection from the project. • Digging and doing tests to complete the require information. • Identifying harms in qualities evaluation vulnerability and preparing a computer model.

Figure 3.3.70 Picture of the project under study.

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Preparing seismic rehabilitation plans to present seismic rehabilitation executions

First step: collecting the information available for rehabilitation target In this stage, which is considered to be a qualities evaluation section of the existing vulnerable buildings. For this example according to structural and architectural plans are drawn available. Therefore the information is gathered and classified based on available documents, and if anything is missing in plans, it will be made available. While there are no test results of welding and concrete ceiling composites, the requisites for existing material specifications will be prepared and presented. • Introducing building use and evaluating its changes Defining and extracting floor specifications for the studied building is one of the most significant in seismic rehabilitation. Because applying gravitational loading and determining importance factor of the building and its floors are necessary, descriptions are given as in the following table. As it was mentioned in the beginning, this building is a 10-storey structure, which has some old and new uses according to the available plans as in Table 3.3.31. To evaluate the quantitative vulnerability, more precise details about the floors is required. Further, more specifications required for evaluation of the floors will be presented (Table 3.3.32). With a qualities view, we can notice that the existing building has a significant increase in live load loading due to the change in its use which can affect the structural system. In this case, based on the definitions of interior areas and beneficiaries, the number of the building users, and special equipment that directly impact loading increase 3 Table 3.3.31 General specifications of the building part one—comparison of initial and new user. Row Floor number Initial user New user

1

First

2 3

Second Third

4

Fourth to tenth roof top

5

Parking and sports Parking Parking

Parking and sports

Residential

Laboratories and laboratories Emergency 1 ambulance parking and lobby Patient's office and hospital room

Roofing

Roof garden and mechanical location

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Table 3.3.32 General specifications of the building part two comparison of initial and new user. Row Floor New user Area Story height number ðft:2 Þ ðft:Þ

1 2 3

First Second Third

4

Fourth to tenth roof top

5

•

Parking and sports Laboratories and laboratories Emergency 1 ambulance parking and lobby Patient's office and hospital room

10763.9 10763.9 6458.35

Roof garden and mechanical location

6458.35

16.40 11.4829 16.40

38750.08 11.4829 13.1234

times approximately, and the importance of the building increases significantly. Introducing the structure Presenting a precise view of the building to evaluate damages and seismic rehabilitation is very important. Therefore we are presenting a thorough description of the current structural system of the building. Fortunately based on the available structural and architectural Plans we can identify precise components and elements without or with little digging. By taking a general look at the structure, it seems that the building consists of several structural systems which work together to perform depreciation gravitational and seismic loading as the following: 1. fully restrained steel moment frame integrated with CBF braces 2. partially restrained steel moment frame 3. partially restrained steel moment frame 1 infill concrete shear walls around the structure

3.3.6.1.2 Structural system type 1 3.3.6.1.2.1 Fully special restrained steel moment frame integrated with CBF braces

As it was mention before and as it can be seen in the plan of the structure, this building lacks structural system consistency. It is in north to south direction with the construction geographical X direction. In the first and sixth frames, the structure has a special moment frame system with (SSMF 1 CBF) braces. In the other frames, however, the structural system consists of separate special moment frames with no braces. The

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gravitational loads in this system is transferred to steel columns through steel beams and finally to the lower structures. This structural system has been performed in the third up to the tenth floor. Seismic and winds loads in this system are carried by the beams, columns, and the braces (Fig. 3.3.71). 3.3.6.1.3 Structural system type 2 3.3.6.1.3.1 Partially restrained steel moment frame

This system has been executed in the third up to the tenth floor in Y or east to west direction in this building. The connections of the beams and columns in this system are intermediate steel moment frame, and as it was mentioned, there is no general frame consistency and the frames are cut off. The gravitational loads in this system are first transferred to the beams and then to the columns through the diaphragm, and eventually to the lower levels and foundation. Seismic and winds loads are carried by the beams, columns, and the connections among them, and the reactions are transferred to the foundation (Fig. 3.3.72).

Figure 3.3.71 Modeling in computer software structural frames with fully special restrained steel moment frame integrated with CBF.

Figure 3.3.72 Structural frames with partially restrained steel moment frame.

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Figure 3.3.73 Structural frames with PRMF 1 infill concrete shear walls around the structure. PRMF, Partially restrained moment frame.

Figure 3.3.74 Roof structure in existing building and Modeling in computer software.

3.3.6.1.4 Structural system type 3 3.3.6.1.4.1 Partially restrained steel moment frame 1 infill concrete shear walls around the structure

The level on the first two floors above the foundation of the structure, steel beams and columns have been constructed with intermediate steel moment frame connections. Therefore all around the frames have been restricted with reinforced concrete shear walls (Fig. 3.3.73). 3.3.6.1.5 Ceiling structure and its function According to the observations and evaluating the structure of the Plans, it was figured out that the constructed ceiling structure in this building is a concrete composite ceiling which has a rigid diaphragm function. Therefore lateral and gravitational loads are spread properly among the beams and columns (Fig. 3.3.74). 3.3.6.1.6 Foundation structure type The foundation of this building is reinforced concrete foundation executed with MAT structural geometry based to the field inspections and available Plans (Fig. 3.3.75).

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Figure 3.3.75 Foundation structure in existing building.

3.3.6.1.7 Qualities evaluations for the existing building 3.3.6.1.7.1 Evaluating the consistency of the building

According to the observations in the structure Plans, and also the presented descriptions in the introduction section of the structural system, it can be concluded that the structural system of the building is not consistent enough to transfer seismic and gravitational loads. Thus since the diaphragm system of the ceiling is functionally rigid, this has to be precisely evaluated in quantitative. 3.3.6.1.7.2 Evaluating the regularity in height of existing structure and its plan

According to the layout of the elements, we can notice that the rigidity distribution in the structural plan is suitable with a qualities view and it seems that the distance between mass center and stiffness is in the range of the regulations, that is, 20% of the building dimension. However, final decision relies on the precise vulnerability quantitative evaluation of the building. About irregularity in height, according to the unique distribution of stiffness and mass in floors, it seems that the irregularity does not exist in this project and the building has a special regularity in distribution of stiffness and mass in floors based on the distribution of elements and weight. According to the loads applied to the building in its new use, live load increases significantly, which has to be evaluated as a parameter. 3.3.6.1.7.3 Evaluating symmetry condition in the plan

In this example, based on the available architectural details, it was observed that there is an unconventional protrusion in the frame of the high cantilever beam at the end of the project structure, which is 8.20 ft long. Since it is not properly braced, it is considered to be vulnerable and

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asymmetrical where its precise evaluation for the gravitational loading will be done in the qualitative evaluation section. 3.3.6.1.7.4 Valuating height to the dimensions of the building

The ratio of height to length or width dimension in this building is less than 3 according to calculations, so it is not considered a thin building. ! !     95:14 ft: 95:14 ft: H H 5 1:5 and 5 0:91 5 5 D D 62:99 ft: 104 ft: N2S E2W

3.3.6.1.7.5 Evaluating opening areas within diaphragm

In this project, based on the architectural and structural plan, it is observed that the ratio of the opening areas to the total area is about 10 to 12%. Since this number is less than 50%, it is not considered vulnerable. Due to the fact that opening areas are generally places which have access to floors, they should be evaluated in the quantitative evaluation section. 3.3.6.1.7.6 Evaluating integration and consistency in accessible areas to the floors

In this case, based on the architectural Plans, it has to be noted that the stairway has be relocated between the lobby and the basement and has led to irregularity in the architectural plan. Also according to the observations, some elements of the stairway lack proper supports in the lobby (Fig. 3.3.76). 3.3.6.1.7.7 Evaluating the existing deterioration, decay, recession

Due to the fact that it is not long before the project has started, and that its components are properly heat isolated and painted, decay in this project is not considered.

Figure 3.3.76 Location of stairways in the floors.

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3.3.6.1.7.8 Introducing the construction site of the current building

Based on the geotechnical specifications and soil shear wave speed resulted from the presented information in the first observations on the construction soil, the soil is type II. (2800) this means that the shear wave velocity of the soil is 375 # V s # 750. 3.3.6.1.7.9 The question left, after the qualities evaluations, is that why this building should be seismically rehabilitated?

• • • • • • • •

Change in loading for about 2 times according to changes in the occupancy of the floors Inconsistency in the lateral seismic system (there is no consistency among the frames both in longitudinal and transversal directions) In regions with very high seismic hazard, using intermediate steel moment frame system is not allowed for the buildings with high importance. Change in expected performance level in structural and nonstructural components Asymmetry in buildings according to existing cantilever beams with free length of over 1.5m without any proper braces in the structural section. Change in roof to garden roof and significant increase in live load Neglecting chords and collectors around the openings in diaphragm areas Having no proper constraint to access the floors due to inconsistency in accessible routes

3.3.6.1.7.10 Agenda to do tests and digging

Presenting a primary list for the required tests and digging (geotechnical and material strength test). Based on the building observations, and according to type of the structure and having access to the structural Plans of the building, considering the lack of information, the executive agenda of digging and tests was set for seismic rehabilitation studies. Concrete strength tests were done on the available concrete shear walls and composite ceilings, tests and diggings, checking welds in columns and connections, tests on shear heads, and checking the quality of fireproof insulation used for the project. 3.3.6.1.7.11 Evaluating quantitative vulnerability of floors

To evaluate the quantitative vulnerability, because the ceiling diaphragm is rigid, a 3D computer model is used in this project to have a better understanding of the damages and its components.

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3.3.6.1.7.12 Determining building configuration

The configuration derived from digging and tests done on the building is available for the existing structural and architectural Plans. The descriptions are presented first and are accessible in plans at the end of this example. • Evaluating configuration of columns for modeling The present building includes 33 columns in the first three floors, which reduces to 24 columns in the top seven floors. This reduction is due to the building occupation area. Generally the box columns used in this project are 11:81 in: 3 15:74 in: and thickness of 1.57 in., and 11:81 in: 3 11:81 in: columns and thickness of 0.47
1.57 in. In adjacent braces in the bottom floors, 11:81: in 3 15:74 in: sections have been used in three floors, and for the other columns, the sections are 11:81ðin:Þ 3 11:81ðin:Þ with different thicknesses. One of the weaknesses of this modeling is lack of proper sorting of the columns, since in the building with a total number of 33 columns, it is so too unwisely to use 22 types of columns. It is important to bear in mind that based on the results, inconsistency in the frames has led to an increase in the number of the sections, and as a result, in the sorting of the columns (Fig. 3.3.77). • Evaluating configuration of beams for modeling Like columns, beams do not have a proper sorting in a project where more than 25 types beam were designed and used the project in the beginning stage. These beams are 9.44 to 23.62 (in.) high with various thicknesses. In these beams, the upper and lower beams flange are designed with the length of 4.92 to 9.44 (in.) and various thicknesses. The lack of proper sorting in beams shows the inconsistency in asymmetrical performance of the structural components due to the lack of connection with structural frames. The beams of the composite

Figure 3.3.77 Evaluating and determine column specifications for use in computer modeling.

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ceilings are all in X direction, which is considered to be an important weakness. However, a more precise remark will be made after qualitative evaluation (Fig. 3.3.78). Evaluating configuration of braces for modeling Braces have only been executed in main frames 1 and 6 evaluation with two crossing braces in each frame for the existing building in the top 8 floors. According to the existing structural Plans and comparing them to execution Plans, it was specified that its dimensions varies from 2unp14 to unp22 (Fig. 3.3.79). Evaluating configuration of existing concrete shear walls for modeling The existing concrete shear walls in the first two floors above the foundation working as interframe element have surrounded the building with reinforced concrete walls with thickness of 15.748 (in.) with 14 to 16 bars and Regular grid arrangement as 7:87 in: 3 7:87 in: These walls have been executed in the frames 1, 6, A, and H. These concrete walls surround the three lower floors of the building (Fig. 3.3.80). Evaluating configuration of existing structure of foundation for modeling As it was mentioned before, the existing building foundation is reinforced concrete with expansive geometry with depth of 49.21 in

Figure 3.3.78 Evaluating configuration of beams for modeling.

Figure 3.3.79 Evaluating and determine of braces detail for modeling.

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Figure 3.3.80 Evaluating and determine of existing concrete shear walls detail for modeling.

Figure 3.3.81 Determining foundation detail for modeling.

above the soil basement with reinforcement 22mm in diameter in the section of 7:87 in: 3 7:87 in: (Fig. 3.3.81). In this section, we have avoided presenting more details on configuration and modeling due to the high number of elements and structural components and we will focus on identifying inconveniencies and their solutions for the readers. 3.3.6.1.7.13 Determining expected and lower bound strength of material based on the test results

Based on the agenda, experiments and digging tests were done on the building and finally, by considering FEMA 356 journal criteria. The required information was extracted from the results of the tests and the catheters (Table 3.3.33). 3.3.6.1.7.14 Soil and foundation

To determine site specifications, a machine borehole is excavated at the depth of about 49.5 ft. The summary of the results is shown in the table to be used in quantitative evaluation foundation (Table 3.3.34).

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Table 3.3.33 Summarizing the presented specifications by lateral counseling services. Member Strength capacity ðIb=in2 Þ Low-bounded (QCL)

Foundation and wall concrete Ceiling concrete Beam and column steel Existing bar in foundation Existing bar in wall and ceiling

0

f c 5 3982:54 f 0 c 5 2986:9 Fy 5 34136:02

Expected strength (QCE)

f 0 c 5 4267 f 0 c 5 3555:84 Fy 5 38403:03 Fy 5 56893:37

Table 3.3.34 Geotechnical test results. Foundation B(in.)

Box

39.3701 78.7402 118.11

Table 3.3.35 Dead and live load. Row Name ValueðIb=ft:2 Þ Row Name

1 2 3 4

Structural ceiling Exterior wall Flooring Interior walls

71.6857

1

114.287 51.204 118.793

2 3 4

Classes with therapeutic use Hallways Roof (Roof Garden) (Snow load)

qa ðIb=in:2 Þ

30.86465 28.87339 26.73989

ValueðIb=ft:2 Þ

71.6857 102.408 102.408 30.7224

Dead load table live load table.

3.3.6.1.7.15 Define gravity load such as dead and live

In the quantitative evaluation section of the building vulnerability, to calculate and evaluate specifications such as gravitational stress, base shear, and overturning, determining gravitational loads of the building is required. Therefore loading dead and live loads should be done carefully. In this project, dead and live loads are shown in Table 3.3.35, respectively. 3.3.6.1.7.16 Determining primary (main) and secondary components in the model and its stiffness

In building modeling, all the beams, columns, braces, and shear walls are fundamental. These components should be precisely evaluated based on presented regulations and ground rules of the rehabilitation formula.

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3.3.6.1.7.17 Foundation modeling

In this example, since the supports are rigid, foundation modeling can be done separately from the structure model. 3.3.6.1.7.18 Primary controls of the building structure

According to geometric dimensions and position of center of mass and center of stiffness coordination in this building, the distance between these two centers in either direction of the building does not exceed 20% of the building dimensions according to the table (Table 3.3.36). In this building, mass distribution in height is almost even where the mass does not exceed 50% of change in any of the floors compared with the mass of the floor beneath it (Table 3.3.37). Table 3.3.36 Calculating center of mass and center of stiffness. Story Diaphragm XCM(in.) YCM(in.) XCR(in.)

YCR(in.)

Roof garden Story 06 Story 05 Story 04 Story 03 Story 02 Story 01 Ground Labratuar Parking

376.67 377.06 376.67 375.89 372.35 370.39 366.47 354.70 331.94 341.36

D1 D1 D1 D1 D1 D1 D1 D1 D1 D1

925.20 924.41 924.02 924.02 923.63 924.02 923.24 881.25 736.86 733.33

370.00 369.61 370.00 370.00 370.39 370.79 371.57 339.79 330.37 326.45

890.28 883.21 883.61 882.04 880.47 875.37 857.71 884.78 737.65 738.04

Table 3.3.37 Mass change percent in building floors. Story Diaphragm Mass X (Kip)

Roof garden Story 06 Story 05 Story 04 Story 03 Story 02 Story 01 Ground Labratuar Parking

D1 D1 D1 D1 D1 D1 D1 D1 D1 D1

1722.03 1461.95 1461.95 1461.95 1461.95 1461.95 1461.95 1914.52 1914.52 2457.25

1.18% 0.00% 0.00% 0.00% 0.00% 0.00% 23.64% 0.00% 22.09%

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3.3.6.1.7.19 Determining and calculating seismic evaluation parameters of the building vulnerability

Earthquake force applied to the building is an important parameter and to evaluate that, first we need to determine efficient frequency period of the structure. The frequency period is determined using the experimental equation below [1]. TX 5 0:795S and TY 5 1:27S Despite the existing concrete shear wall fender in both directions and all around the building, due to proper consistency among the structural frames, the height of the building is considered for the basic level from above the foundation. The reason for that is inconsistency among structural frames. The efficient frequency period resulting from dynamic calculations by computer modeling in X direction is 1.34 and 2.217 seconds in Y direction. As it can be seen, dynamic efficient frequency period equals 1.8 times more than experimental efficient frequency period. Therefore experimental efficient frequency period can be increased to 40% and the purpose of the contract, since frequency period in Y direction is more than X direction, it shows that the structure has less stiffness in Y direction than the other direction, and so it will have more displacement against earthquake in this direction Furthermore, based on the fact that the frames in this direction are partially restrained steel frames (intermediate moment frame) which should to a system with more capacity. So that, since mass distribution percentage in the first and second frame modes are 50%
60% in both X and Y directions, it is recommended that seismic rehabilitation method is used which increased distribution percent up to 70% within the frame mode. Behavior of the beams in this project is based on geometric condition and loading control by transformation. The columns in top and bottom floors are force-controlled. Cantilever beams which are free in one side have controlling behavior by transformation. Therefore quantitative rehabilitation evaluation in the example above will be extracted from computer modeling based on numerical calculations (Fig. 3.3.82). TDX 5 1:345S and TDY 5 2:127S ; Sax ðBSE 2 02Þ 5 0:468 and Say ðBSE 2 02Þ 5 0:341 Calculating seismic lateral force applied to the building δ 5 C0 :C1 :C2 :C3 :Sa ðBSE-02Þ 3

Te2 3 g-δtðyÞ D25 in; δtðxÞ D17 in 4π2

Figure 3.3.82 Diagram of target displacement on x direction for existing building.

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3.3.6.1.7.20 Extract and Present Analysis Results

After qualitative evaluation, according to FEMA 356 criteria, the following existing structural damages were observed based on new building use: • Most of the columns have high DCR and need seismic rehabilitation • Some of the beams are weak in terms of bending capacity, which should properly become rehabilitated seismically. • New loading has caused the structure to bear more loading compared with its prior condition. As a result, the total structure rehabilitation is evaluated. • Gapping through accessible routes is considered to be one of the architectural weaknesses based on its new building use, which should properly become architecturally reformed. • Very high vulnerability of south façade cantilever of the building 3.3.6.1.7.21 The following methods are recommended to solve the problems mentioned above

• • • • • • • •

Change in the stairway location from lobby floor down to lower floors to correct load transmission to contrive proper lateral seismic systems in diaphragm. Using secondary elements like, concrete shear walls and buckling restrained braces to increase stiffness and accordingly, to increase its component resistance and elements. Using new braces in frames 1 and 6 to improve stiffness Preparing and rehabilitating the existing beams in frames 1 and 6 to increase resistance. Eliminating the inconsistent structural systems subjoining shear walls to ceiling diaphragm. Seismic rehabilitation of foundation level where new shear walls join. Due to surrounded of the building structure in the two lower floors and displacement of the floors in these floors which is almost zero, concrete shear walls can be used with articular support. Constraining façade structure properly and cantilevers in the south façade of the building by preparing steel truss beneath the lobby level and joining passive fuse short column to prevent vertical transformation.

3.3.6.1.7.22 Analyzing seismic rehabilitation plan

Examination of plastic hinge formation in components: As it can be observed from analyzing and modeling results, stiffness of the structure has

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been increased in both directions due to providing new concrete shear walls. This can cause the resistance of components to increase significantly, and the elements which were vulnerable in the quantitative evaluating section not to be vulnerable anymore. The columns are no longer vulnerable due to an increase in stiffness provided with new concrete shear walls, and consequently, can endure the applied load in the structure in a proper way. In the following picture, drift of the floors whether before or after seismic rehabilitation has been compared in both directions (Figs. 3.3.83 and 3.3.84). An important note to consider is the relation between rigid diaphragms with new elements, that is, extension concrete shear walls. In the area of this connection, connections are designed according to the joint for restrained the displacement cause by diaphragm load. Finally, in this region, by providing extension elements which is presented down the picture, new concrete shear walls will be connected to the diaphragm by using steel pieces (Fig. 3.3.85). Presenting calculation to design extensions of new concrete shear walls and rigid diaphragm (Fig. 3.3.86). In the region with new concrete shear walls and foundation, as it was mentioned, according to negligible deformations in the first-floor level, a system of shear walls with articular heel can be used by making a GAP (Fig. 3.3.87). 3.3.6.1.7.23 Seismic rehabilitation of long cantilevers and façade components

Constraining façade structure properly and cantilevers in the south façade of the building by preparing steel truss beneath the lobby level and joining passive fuse short column to prevent vertical transformation (Fig. 3.3.88). 3.3.6.1.7.24 Seismic rehabilitation by changing the stairway location

Change in the stairway location from lobby floor down to lower floors to correct load transmission to contrive proper lateral seismic systems in diaphragm (Figs. 3.3.89 and 3.3.90). 3.3.6.1.8 Example of tall building 18-story steel special moment frame building 1 concrete shear wall with SMD rigid diaphragms

3.3.6.1.8.1 Introduction

The building under study in this example is located in the north region of Tehran. This building includes 18 floors with three parking floors, a pilot

Figure 3.3.83 Evaluating plastic hinge was created in elements.

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Figure 3.3.84 Diagrams for evaluating the displacement of floors: before and after seismic rehabilitation.

Figure 3.3.85 Methods for connecting new concrete shear walls to existing roof and exiting foundation.

Figure 3.3.86 Methods for connecting new concrete shear walls to existing beam and column.

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Figure 3.3.87 Making a GAP between new shear wall and existing foundation.

Figure 3.3.88 Add new truss for seismic rehabilitation cantilevers.

floor, and 14 residential floors. The top floor of the building is also a roof garden with a tower meeting room. The building was built on 25833:39 ft2 of land, which was designed in 2010 and the first phase of the structural skeleton was completed in 2012. After 2012 according to the new urban planning rules, the building could be classified as a luxury building. In 2012 the builder decided to revise the architecture of the building according to the location of beams and columns. In the initial state of the structure, the building has a structural system of partially restrained steel moment frame with reinforced concrete shear wall. The parking floors is also encased in a series of reinforced concrete shear walls (Fig. 3.3.91). The structure of the foundation is reinforced concrete with semideep piles in the heels of the mediate concrete shear walls. The new architecture included the construction of larger units, the roof garden and the auditorium on the rooftop floor, and the construction of a pool and gym

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Figure 3.3.89 Changing stairway location.

and a hypermarket on the lobby floor. According to the criteria presented in FEMA 356, this building should be evaluated for the purpose of seismic, and baseline rehabilitation to provide life safety in earthquake hazard level one. In this regard, the following will be considered and evaluated in the above example. • Is the existing building vulnerable to architectural changes based on the expected seismic rehabilitation goal? • What are the strengths and weaknesses of the building after analyzing the existing structure? • What are the proposed seismic rehabilitation strategies and methods for the existing building? The steps of seismic evaluation and seismic rehabilitation for the building under study are as follows: • Modeling of the existing building based on FEMA356 and iranian code No.360 with respect to new architecture. • Evaluating nonlinear vulnerability and interpretation of strengths and weaknesses in the case study based on the new architecture. • Modeling seismic rehabilitation methods according to the new architecture and preparing execution and financial and temporal evaluation Plans of the existing example.

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Figure 3.3.90 Some seismic rehabilitation operations are considered, for example one.

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Figure 3.3.91 Aerial photo of the project under study in this example.

3.3.6.1.8.2 Step One: Building modeling for simulation

In the example, given that all structural Plans are fully available and also new architectural Plans are in accordance with existing structural Plans, considering the architectural drawings, it was found that there would be changes in the existing structure, mainly in locating and removing secondary seismic systems such as shear walls and openings in the roof diaphragm and changing the location of volatile stairs. Also the steel and concrete components used in the building have been carefully designed and tested during the construction process. Given the availability of this information on the one hand and the structural drawings plans that have been verified by the executing agents on the other, full 3D modeling can be performed. Whatever is needed for the modeling of this example and should be extracted from the Plans and test results during manufacture. Comprehensive structural information of the structure including: 1. Type of structural system in the building, type of diaphragm, type of foundation and type of lateral seismic system 2. Geometrical properties of sections and the floors and their locations 3. Specifications of strength of materials used in the building 3.3.6.1.8.3 Compiling and extracting comprehensive structural information of the building structures for accurate modeling and comparing them to existing structures

•

Type of structure: in this building in this example, as mentioned above, is a steel structure consisting of I-shaped beams and box columns designed

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and executed by intermediate moment connections in accordance with the standard design requirements of steel structures. In this building, gravitational load conveying system is steel beams and columns. Despite steel beams and columns, a number of interstitial reinforced concrete walls have been distributed in the structural plan, which has been considered on all floors in the primary structure (prior to seismic rehabilitation and architectural changes). Due to the proximity of the neighborhood on the north side and the presence of soil on the adjacent building on which there are local access roads, the structure is sheathed by reinforced concrete walls which play a significant role in conveying heavy loads to the foundation. Since the cross section of the walls is significantly higher than the floor cross section, their lateral performance is more pronounced than their gravity function. Type of story diaphragm: according to the type of ceiling of this building, which is Steel Metal Deck, based on the definitions given in Chapter 1, Understanding the basic concepts for seismic rehabilitation, this type of ceiling has displacement and deformations in rigid behavior, so a rigid diaphragm is considered. But it should be noted that the Chords and Collector border elements seem to have not been properly designed. Therefore these areas should be subject to a precise quantitative evaluation. Also since the structural ceiling system consists of a reinforcement grid, along with a corrugated sheet metal mold, creating any new openings in these ceilings results in a disruption to the diaphragm load transfer system and the stress concentration in the manipulated areas. Therefore with regard to the new architecture, it is recommend that the location of the openings and the load distribution system be carefully evaluated. Type of foundation: structure under study in this building is a deeply expanded foundation with semideep piles installed at the foundation against the boundary area of these walls. In the modern engineering perspective, however, the relationship between the retain wall and foundation is considered integrally in the analysis and evaluation of the foundation. Existing Materials used in foundations in accordance with existing Plans and tests of strength of materials during construction are normal strength concrete including AIII grade rebar’s in upper and lower meshes which should be considered in quantitative evaluation considerations. Seismic lateral restrained system: in this building includes bending behavioral performance influenced by the relationship between concrete shear walls and the framing structure in Boundary element method on

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•

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the one hand as well as and also the partially restrained moment steel frame that have a good performance during earthquakes. It seems that it is appropriate to use this method for the number of floors with residential use and expected performance in the building. But the final decision to announce the result will lead to a quantitative evaluation of the vulnerability based on the FEMA 356 criteria that will be presented below. It is worth noting that, if possible, some shear walls based on new architecture in the upper floors should be removed or replaced with a new seismic system, which will be examined in detail. Geometrical properties of structures: main plan of this building is implemented on a 130.57 ft. 3 194.22 ft. 1/2 m2 land where the area of the upper lobby reduces to 8611.13 ft.2 with small demotions in length and width. Structural geometrical properties of the existing structural Plans were verified with specific conditions and it was found that all sections were exactly in accordance with the presented Plans. Also the building plan has irregular geometry which is visible in the attached pictures. Due to changes in the new architecture, like creating a dome-shaped space on the roof floor for the 64.58 ft. height using as the hall and the change of roof use to the Roof Garden and partition of the lobby space of approximately 8880.23 ft into a two-story ledge for use as a warehouse, sports and pool to have a precise evaluation of changes in loading and seismic vulnerability. Height of floors: the floor height in each residential section is 11.15 ft. and so it sums up to 156.16 ft. height for 14 floors. The height of the lobby floor, the first and the second parking floor, and the parking floor above the foundation are, respectively, executed to be 19.52, 9.67, and 11.81 ft. (Fig. 3.3.92).

3.3.6.1.8.4 Three-dimensional simulation in computer software

Given that both the diaphragm is rigid and the cohesion between components constituting the structure is consistent, two-dimensional and threedimensional models can be used to evaluate vulnerability, for example. In this example, due to the multiplicity of structural components and the avoidance of possible errors, 3D computer modeling is used for seismic evaluation and rehabilitation (Fig. 3.3.93). 3.3.6.1.8.5 Additional information to evaluate qualitative vulnerability

•

Groundwater Survey and History of Liquefaction: in this example has been palace at the base mountain height, so it is not topographically

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Figure 3.3.92 Elevation for evaluation of height of buildings stories.

Figure 3.3.93 3D modeling the structure for more accurate evaluation of structural behaviors.

•

relevant. Groundwater levels are more than 131.234 ft., so the fluidity in this example is not relevant. Determining the seismic rehabilitation objective and its quantitative parameters The purpose of the seismic rehabilitation intended for the existing building is to rehabilitate the baseline. To provide life security against earthquakes at risk level one (BSE-1(B10%/50 year)), this goal should be considered for both structural and nonstructural members.

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Determining the coefficient of knowledge factor Based on the existing structural Plans and test reports and the required complete and accurate information about used materials for this example, no digging or testing were done, so considering the above, the K knowledge factor is considered to be one. Evaluate the proximity of the existing building to the surrounding buildings In this example, considering the location of this building, it only shares the negative seasons with the neighbors in negative alignment and only on one side of the north side. Therefore the area is also reinforced by concrete walls and soil consolidation operations in the nailing mode (Fig. 3.3.94). Evaluating executive weaknesses in the primary (main) and secondary components Considering that during the presentation stage of the new architectural changes, the structure of building was fully visible and according to an eye inspection it was found that there was no deflection rusting, or frazzle in the steel components. Also no cracks or deterioration were observed in the walls and foundations of concrete materials. There was no corrosion or tear in the roof components. As a result, it is clear that the existing material is in good condition. Ratio of height to building aspect The height of the building from the foundation is 206.85 (ft.) and the length and width of the building is 194.22 (ft.) and 39.8 met 130.57 (ft.), respectively. Thus for the existing building, considering the dimensions, the ratios are in standard and even smaller ranges and the building is not vulnerable.

Figure 3.3.94 Evaluate the proximity of the existing building to the surrounding buildings.

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  H D

0 5@

N2S

•

1 206:85 ft:A 5 1:06 and 194:22 ft:

  H D

0 5@

E2W

1 206:85 ft:A 5 1:58 130:57 ft:

Irregular situation

3.3.6.1.8.6 Evaluating the situation in the building plan

The building in the plan has no symmetry in terms of dimensions on the top floors (lobby) form the pilot floor. One of the disadvantages of this is the geometry of the architectural plan since it leads to an increase in asymmetric distribution of stiffness and eventually an increased likelihood of curvature. According to the extracted results, based on the qualitative engineering judgment, the plan geometry seems to be irregular due to the poor distribution of the walls. In this building, torsions may occur during the earthquake. Therefore it is recommended to perform a quantitative analysis and precise evaluation in the quantitative evaluation section of the distance between the center of stiffness and mass according to the regulations. 3.3.6.1.8.7 Evaluation of irregularities in building height

About the irregularity in height given that the height of the lobby floor is very high, which means something about 80% higher than the height of the upper and lower floors, It seems that the lack of stiffness in this floor has caused the building to be irregular and needs further investigation (Fig. 3.3.95). But in terms of floor mass almost all floors are the same and regular. Due to the shear wall distribution in the plan and the type of seismic lateral restrained system it seems that the lateral resistance of the structure is the same for both directions, but the stiffness distribution in the western part of the example is greater than the eastern part due to its geometry. In this building no asymmetrical cantilevers have been executed as well as no unconventional entanglements in terms of geometry. • Site features from a seismic perspective The soil specifications of the site is based on geotechnical studies carried out at the time of the initial design, indicating that shear wave velocity is in the category of 175 # V s # 375. Soil type has a significant impact on the evaluation and calculation of Ss the existing structures and according to the completeness of available information,

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Figure 3.3.95 Modeling to assess geometric irregularities in height for the studied building.

•

•

•

testing is not required and the existing specifications can be used in the reports. The condition of the opening areas and their proximity to the stories diaphragm Since the structural system of the building has been framed, it is not necessary to check the status of the window openings to assess the vulnerability of the frame, but how to position the windows for the analysis and evaluation of infill frames, mainly of clay brick building materials is required to control the in plane and on plane buckling. According to the building existing architecture plans on the whole level of floor area, the area of the openings is less than 15% of the total surface area. Since this number is below 50%, it is within the permissible limits according to the regulations. Mass and stiffness changes in the new architecture plan According to the new architecture presented, it seems that the new weight of about 2204:62 Ib will impose a surplus on the initial weight of the structure. Compared with the initial weight of the building, if the weight of the average building is 163:853 Ib=ft2 , this figure is estimated to be around 43651528 Ib. In comparison, we can see that the mass change of the building is less than 20% which is a very small value. Determining the expected and lower bound of the material strength according to As mentioned earlier in this example, due to the complete required information on the quality and material resistance, one can obtain the information required on usage material strength from the information

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contained in the tests performed at runtime and the information contained in the Plans. As a result, the steel components are considered to be Fy 5 34; 136:02 Ib=in:2 and, Fu 5 55471:04 Ib=in:2 and for existing bars which are mainly of AIII are Fy 5 56; 893:37 Ib=in:2 and 0 Fu 5 711; 16:72 Ib=in:2 . For existing concrete FC 5 3555:84 Ib=in:2 is considered. Given that the present information is extracted from the Plans, the both of the parameters in this building are equal. Quantitative evaluation of building’s components needs for seismic rehabilitation Quantitative evaluation of the vulnerability in this building will be done according to the FEMA 356 of Improvement Approaches. Therefore the computer modeling is used for a precise evaluation of the behavior components of the structure. As we know, in modeling the existing structure and extracting behaviors, the most important step is the geometric and dimensional modeling of the building structure and loading such as construction. These loads for the existing example include live and dead loads based on new architecture and geographical patterns, roof snow loading, and seismic loading on existing buildings. Gravity Super dead loads, Super dead loads are basically superimposed dead loads which are applied on a structure. So, for example, self-weight of the slab is dead load while the load of any finished, partitioning, cladding, false ceiling are all super dead loads. In accordance with the floor plan elaborate work of the floor, regardless of the ceiling slab load per square foot, is 61.5 Ib/ft.2 in the residential class, 51.20 Ib/ft.2 in the parking lot, and 71.68 Ib/ft.2 in the lobby and 102.40 Ib/ft2 in the roof. Depending on serviceability, the gravity live load for per square foot area is 102.40 Ib/ft.2 of lobbies and parking, 40.96 Ib/ft.2 of residential floors and 30.72 Ib/ft.2 of snow and 61.50 Ib/ft.2 of roofing as roof Garden (Fig. 3.3.96). Modeling primary (main) and secondary components In this example, the modeling of the primary components include the beams, connection, columns, is done in full with all the details available in computer modeling and effective of secondary components such as foundation and walls define in structure model. Non structure members including façade details and stair beams and joint details, electrical and mechanical elements such as elevators, chillers, motors and brick interstates are independently evaluated in a separate file. The effects of the infill wall due to their low stiffness are not considered in the structure but their weight is calculated and applied in modeling. The modeling of the foundation due to the rigidity of the supports and the interaction

Figure 3.3.96 Gravity dead and live load on building’s stories.

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Figure 3.3.97 Structural and architectural simulation for modeling primary and secondary components.

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curves of the soil and structures can be independently created and the forces required to extract them from structural modeling and applied to the foundation modeling independently. The modeling that is analyzed to assess vulnerability is based on new loading and removal of shear walls in the last three floors of the building and the addition of new structures such as a dome, gym and pool (Fig. 3.3.97). Seismic loading Lateral seismic loading, for example, is done in accordance with the FEMA356 and Iranian codec 360. In this regard, the efficient frequency period of the structures in both X and Y directions is calculated based on experimental formulas. Finally, according to this and other seismic parameters, the earthquake lateral force was calculated using the following formula for the building. Calculating V C1ðxÞ 5 1; C2 5 1:0; C3 5 1:0; C0 5 1; Sax 5 0:371; Say 5 0:356 VX 5 0:371 W ; Vy 5 0:356 W

•

Introducing load combination In the existing structure, the loading compounds are based on the FEMA 356 loading compounds as presented below. These load compounds are used in the quantitative evaluation section to control the forces controlled by force and deformation as follows. 8 < QUD 5 QGn 6 QE QG1 5 1:1ðQD 1 QL 1 QS Þ g- QUF 5 QGn 6 QE QG2 5 0:9ðQD Þ : C1 C2 C3 j

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Figure 3.3.98 Evaluation DCR of components.

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In the current building, we need to calculate the DCR of the members to evaluate the vulnerability of the members. Therefore it has been determined from the studies that the columns are forcecontrolled according to their structural behavior where. DCRFC 5 QUF =KQCL On the lobby floor where the columns are high, they are controlled by deformation DCRDC 5 QUD =mkQCE . The beams are also have deformation control behavior. The concrete shear walls in this building are considered to be equivalent columns and are controlled by force (Fig. 3.3.98). Evaluating roof structures The concrete structure behavior of the steel deck of the roof is mainly force-controlled because the beam and slab interactions are controlled by deformation which means that the behavior of the studs (rosettes) are controlled by deformation. However, according to the computational complexity of this part of the behavior in the linear domain which is governed by the prescribed rules and relationships based on the maximum shear capacity of the slab. Computer modeling accuracy control building structures We need to determine accuracy of the building modeling with any software. In this way, computer modeling is carefully evaluated to assess the accuracy of modeling: Choosing analysis mode After analyzing the structural oscillation modes, it was found that the percentage of structural mass participation in the oscillation modes in the first, second and third modes is 76%, 80%, and 84.3%, respectively. Also given that Te is smaller than 3.5Ts, according to the material presented in previous chapters and FEMA 356, this estimation

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suggests that the choice of linear static analysis method is appropriate for the structure. Te , 3:5Ts -1:42S , 1:75S-OK By examining the deformations created in the structural oscillation modes, it was found that the modulus is in the Y direction and the modality is in the X direction and the third mode has a curvature function. Overall, 54 modes have been evaluated and analyzed in computer modeling in this building. As mentioned before, the parameters required for structural member analysis and structural DCR extraction were determined according to FEMA 356 tables for beams, columns, concrete shear walls and joints. Following is an example of calculations for better understanding the concepts. Due to the modified loading based on the new uses defined in the building architecture plans, we continue to investigate the center of mass and stiffness to account for irregular effects on the structure, where the distance between the center of mass and the stiffness of the structure is based on Table 3.3.38. The following is presented as a model to evaluate the effects of twisting. 3.3.6.1.8.8 Interpretation

The description of the seismic lateral force in the floors and its relation to the lateral displacement of the floors in the attached image illustrates that the mass distribution in the floors has a suitable condition and the stiffness distribution has a good condition but as mentioned in the new modeling based on the changed architecture plan, it has been removed in the last three floors of the concrete shear wall structure, which has resulted in the Table 3.3.38 calculation of mass and stiffness center. Story XCCM YCCM XCR YCR Story

Parking-3 Parking-2 Parking-1 Lobby Story 1 Story 2 Story 3 Story 4 Story 5

111.4 110.5 110.5 108.2 107.1 107.0 106.9 106.8 106.7

50.0 49.8 49.8 48.1 46.7 46.7 46.7 46.6 46.6

125.3 129.8 129.8 135.5 132.3 129.9 128.5 127.5 126.5

47.6 47.9 47.9 93.5 88.4 84.1 81.2 79.1 77.6

Story Story Story Story Story Story Story Story

6 7 8 9 10 11 12 13

XCCM YCCM XCR

YCR

106.6 106.4 106.3 106.0 105.7 105.4 105.5 105.4

76.4 75.3 74.4 73.6 72.8 70.1 66.5 63.4

46.6 46.5 46.5 46.4 46.3 46.2 46.1 45.9

125.5 124.5 123.6 122.7 122.1 119.2 115.1 111.9

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soft performance of the building structure in these floors. Therefore the deformation of the floors is more than that of the concrete shear wall, and therefore, needs a seismic rehabilitation plan when it comes to preparing the final concept of retrofitting methods (Fig. 3.3.99). Removal of concrete shear walls in the last three floors has made some columns vulnerable. In this regard, the stress ratios of the columns are in the range of 0.8 , DCR ,1.4 Thus it seems necessary to use appropriate seismic rehabilitation systems in this process to reduce column vulnerability. Heavy weight incorporation on the roof has made the roof's approximate weight about 300 tones, and the weight gain has made some columns agitated and in dire need of seismic rehabilitation. • Decorative dome is located on the roof using as the meeting hall, the roof has been constructed as an independent structure. Due to its mass and stiffness, it is necessary to design appropriate connections between the roof structure and this dome at the border element. Examples of fitting and seismic rehabilitation methods for this particular element are presented in this section (Fig. 3.3.100).

Figure 3.3.99 Modular simulation of structural oscillation modes.

Figure 3.3.100 Show dome on existing structures.

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Lobby floor evaluation: due to the changes in the lobby floor, it was found that the effective height of this floor was 234.25 in. divided into two floors of 118.11 and 116.14 in. for warehouses. In this regard, its loading was modified as shown below in this floor. That is, in the part of the floor where the warehouses are, the live load was changed from 102.40 to 71.68 Ib/ft.2 per floor (totally 143.371 Ib/ft.2) per square foot. Therefore seismic rehabilitation measures and detailed evaluations should be made with the intention of incorporating the new structural system (Fig. 3.3.101). Lobby floor survey (sport area): in the lobby sports area this area is divided into two parts: GIM saloon and pool. In the GIM section, the live load is approximately equal to the first live load, but in the pool, dead and live loads are significantly increased. This means that the dead load will increase almost twice as much as the live load from 102.40 to 308 Ib/ft.2, thus making the building vulnerable to the lower floors. The impact of seismic loading on the lower floors is due to the presence of retain walls and middle shear walls cause drift of this floors near zero. Therefore damage is more likely to be caused by gravitational loading. Foundation: According to the studies, due to the lack of variations in seismic loading on the one hand, and low changes in the weight of the structure of the upper building, the overall changes in the weight of the structure are very limited. Therefore the foundation whose main task is to bear the structural weight and transfer the gravity and lateral loads to the soil under the foundation is well done. Considering the slight weight changes, it can be concluded that lateral loading did not have significant changes and no significant effects on the foundation. In this regard, by evaluating the behavior of the foundation, which is

Figure 3.3.101 Show the effects of lobby changes on existing structures.

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Figure 3.3.102 Show the foundation on existing structures.

controlled by force, it can be concluded that the foundation has a good load bearing condition. The final comment will, of course, be postponed when the final seismic plan is presented (Fig. 3.3.102). • Investigation of the need for increased building stiffness in the upper floors: The increase in building stiffness is mainly caused by the incorporation of members of high stiffness or weight loss to reduce the relative displacement of the floors. In this project, due to the stiffness required in the floors, it was adequately supplied, but only in some columns, based on quantitative evaluation, the stresses exceeded the permissible range. In this regard, based on the secondary loading, the need for refurbishment of beams and columns in the upper floors does not seem to increase the stiffness of the floors. • Investigating the need for increased building stiffness in the lower floors of the lobby: In the mentioned floors, to reduce the relative displacement (story drift) of the floors, increasing the stiffness of the floor is a serious issue. Therefore to complete the load transfer path and reduce the relative stiffness of the floor when submitting a seismic rehabilitation plan, concrete shear walls will be used to increase stiffness. The seismic rehabilitation methods used in this example will mainly focus on the upper floors to increase member strength. Many problems will be overcome with increasing local member’s strength. • Seismic rehabilitation methods These suggested seismic rehabilitation methods for existing building components based on the new architecture include: 1. Using steel plates to reinforce columns and some beams to increase strength where in this case the stiffness of the floor will remain almost constant.

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2. Using EBF brace with transplanted beams, where in this case, the middle area of the transplanted beams will also be strengthened. It should be noted that in this case the stiffness of the floor is slightly increased and also increases the strength of the columns. 3. The use of shear walls with openings based on the new architecture in this case leads to a combination of steel columns and shear walls. Likewise, the stiffness of the floor increases significantly and eventually increases the resistance of the floor members. This method is used for simplicity in execution and low cost. Note: Due to the removal of shear walls in the three last floors and a decrease in stiffness and mass increase cause, some columns due to reduce the stiffness of the floor are not resistant to earthquake and stress in such components is slightly above the seismic accept criteria limitation. Therefore it is suggested that in these floors, a local or interventional seismic rehabilitation system be used to increase the resistance of vulnerable members in the lobby floor due to the incorporation of swimming pool and sports zone in lobby floor. • Applying structural changes in the seismic rehabilitation process In this case, computer modeling is done by structural changes, and after completing and introducing new systems and methods, the above example will be refined, evaluated and analyzed, as can be seen by adding concrete wall under the lobby floors. To accommodate the new pool and sports center in the lobby area, the displacements of parking under lobby floor have been greatly reduced. In this regard, the location of the earthquake force (BSE -1) in the lobby floor level can be considered and use divergent brackets to observe the building's architectural plan. • Calculating target displacement in both directions C1ðxÞ 5 1; C2 5 1:1; C3 5 1:0; C0 5 1:5; Sax 5 0:3944; Say 5 0:371 δt ðxÞ 5 17:15 3 1:5D26:57 in:; δtðyÞ 5 19:7 3 1:5D29:5 in: The reason for the approximate similarity of the periodicity of the building in both directions is that the stiffness of the structure is the same in both directions. Given the stiffness distribution and the efficient periodicity, which are almost identical in both directions, we can see that the displacement target in both directions can be assumed to be equal to 27:17ðin:Þ. This relocation is covered under the loads combination applied to FEMA 356. According to the plastic hinges defined

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Figure 3.3.103 Show the target displacement on existing building.

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for beams M3-3 and for the PMM columns, the plastic hinges will be assigned to each section according to its properties and will finally be analyzed on an applied pushover method (Fig. 3.3.103). Interpretation of nonlinear analysis of beams: considering the extracted results from plastic hinges formation experiments, when the structure is capped to the target displacement, all the plastic hinges formed for the beams are mainly in the IO-LS range; hence, meeting the performance requirements of the beams. It is to be noted that some beams are located on the upper third floor in the LS-CP area, which require a seismic rehabilitation. Interpretation of nonlinear analysis of columns: due to the extracted results of the plastic hinges formed in the columns mainly located in the LSCP area, where this range is very small as it can be considered on the LS. But for the greater confidence, the steel jacket system can be used for seismic rehabilitation of the columns. Evaluating of analysis of roof floor and dome shape: this area is individually constructed and is circularly shaped above the roof floor. By extracting point loads and adapting them on the roof of the structure, designing sites and seismic rehabilitation operations of existing buildings were done.

3.3.6.1.8.9 Interpreting seismic rehabilitation methods in the 16—18 floors of the existing building according to the new architecture

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Seismic rehabilitation by the attachment of concrete shear wall with openings In this method, the modeling is done by incorporating new shear walls with opening area embedded in frames for architectural communication (Fig. 3.3.104). The upper frames of the existing wall and column interactions are taken into account and then given the new effective stiffness and strength, the specifications of plastic hinges are defined for nonlinear

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Figure 3.3.104 Shown nonlinear behavior for seismic rehabilitation by add concrete shear wall with openings.

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behavior in the member. Due to the target displacement applied in this type of seismic rehabilitation, it was shown that the members exhibited good relative strength as well as the nonlinear behavior of the members of the IO-LS range. Seismic rehabilitation by EBF bracing method In this method, the modeling is done by attaching EBF braces to the upper floors of the structure by considering openings. Therefore we should keep in mind that the behavior of the Link beam since its length is relatively long in this example is force-controlled. For this reason, the plastic hinges are defined according to the criteria stated in FEMA 356 and finally the structure push over as a value of displacement target to nonlinear analysis and evaluation. Finally the results are extracted by computer modeling. According to the extracted results based on the push over analysis and the target displacement, all plastic hinges are formed mainly in the IO-LS region, but in some columns and beams they are still beyond the LS region and ultimately vulnerable. They should be seismically optimized independently. Local seismic rehabilitation by adding plate on existing columns and beams In this method, increasing the strength and stiffness of the components is done locally so that the members are reinforced by the attachment of new steel plates to vulnerable beams and columns. The beams are reinforced to increase flexural strength and columns for PMV. This operation will often be carried out on the last 3-storey columns and some of the lower floors, and eventually, leading to seismic structural rehabilitation. By incorporating this seismic rehabilitation method, all members will be within the IO-LS seismic rehabilitation range (Fig. 3.3.105). Comparison of the presented seismic rehabilitation practices In the seismic rehabilitation method with the extension of the reinforced concrete shear wall attachment, due to the seismic rehabilitation

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Figure 3.3.105 Shown method for local seismic rehabilitation by adding plate on existing steel components.

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process, the time required for seismic recovery is 60 working days, which was executed by semiprofessional reinforcing and concreting operations. Also to increase the stiffness of the floor relatively much, the problem of many columns is also solved and there is no need for seismic rehabilitation in those floors. Compared with the first method, seismic rehabilitation with using EBF braces requires 45 working days. It is true that time is reduced, but it should be noted that vulnerable elements such as columns and beams are still significantly greater than those of concrete shear wall attachments. We also need professional human resources to build and incorporate these elements and reinforce the link beams. Improvement operations by incorporating PLATEs reinforcing columns and beams for steel jackets require 90 days of relatively professional manpower. The volume of executive operations in the method of attaching EBF braces is greater than that of concrete shear wall and steel jacket. In this regard, it seems that the method of attaching concrete shear walls with openings for floors 16-18 is the best option. Of course, to reinforce some of the beams and columns in the floors below is the use of a steel jacket. Seismic rehabilitation in floors 1
3 In the lobby floor, as it is said, the floor height is 234.25 in. Therefore due to the high height of the middle columns, it seems to preventing lateral buckling of the columns, getting help from a new architecture plan that incorporates warehouses would be very helpful. In this case a number of columns adjoin to gather with new beams. For this reason, the length of the columns is reduced and their behavior changes from the deformation-controlled to force-controlled. In

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this case, lightweight steel elements will be used for adjoining structures for loading and flooring in the warehouses. This workflow is presented in Fig. 3.3.106. In the development section of the sports section, to control deformation caused by heavy concentrated loading and lateral seismic loading caused by pool water and its extensions, one of the appropriate options is by reinforcing slabs and enclosing reinforced concrete walls. As a result, the following steps are recommended. In this case, the floor of the lobby and lower floor will significantly increase the stiffness and resistance of the floor, and eventually tension in the members will be limited. It should be noted that generally due to the multiplicity and concentration of the walls, the displacement of these floors is very minor and the members bear the effective of gravity load combination (Figs. 3.3.107 and 3.3.108).

Figure 3.3.106 Implement lightweight steel structures to create warehouses on the lobby floor.

Figure 3.3.107 Seismic rehabilitation method in the structural zone under pool and sport area.

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Figure 3.3.108 Some seismic rehabilitation operations are considered, for example, two.

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References [1] American Federal Emergency Management Agency (FEMA.356), Prestandard and Commentary for the Seismic Rehabilitation of Buildings, Reston, VA, November 2000. [2] Islamic republic of Iran Vice Presidency for Strategic Planning and Supervision: (code. No.360) first revision, Instruction for Seismic Rehabilitation of Existing Buildings, Office of Deputy for Strategic upervision, Tehran, 2014. [3] American Society of Civil Engineers (ASCE/SEI 7-10), Minimum Design Loads for Buildings and Other Structures, Reston, VA, 2010. [4] Islamic Republic of Iran Management and Planning Organization: (code.No.376), Instruction for Seismic Rehabilitation of Existing Unreinforced Masonry Buildings, Office of Deputy for Technical Affairs, Tehran, 2007. [5] ASCE, Seismic Rehabilitation of Existing Buildings (ASCE/SEI 41-13), American Society of Civil Engineers Reston, VA, 2013. [6] Federal Emergency Management Agency (FEMA), NEHRP Commentary on the Guidelines for the Seismic Rehabilitation of Buildings: (FEMA 274), FEMA, Reston, VA, 1997. [7] Federal Emergency Management Agency (FEMA), Prestandard and Commentary for the Seismic Rehabilitation of Buildings, FEMA, Reston, VA, 2000.

Further reading American Concrete Institute American Concrete Institute: (ACI 318/14), Building Code Requirements for Structural Concrete, Farmington Hills, 2014. Iran Road, Housing & Urban Development Research Center (Iranian Standard . 2800), Forth Edition of Building Design Codes against earthquake,Tehran,2015.

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CHAPTER FOUR

Nonstructural components: detailed introduction of its types and methods of seismic rehabilitation Aims By reading this chapter, you are introduced to: • • • • •

comprehensive introduction to nonstructural component categories; fast vulnerability assessment methodology; detailed vulnerability assessment methodology; seismic refinement methods for nonstructural components; and the chapter topics in depth by studying two practical examples at the end of this chapter.

4.1 Types of nonstructural components Generally, a building consists of both structural and nonstructural components that must be thoroughly analyzed and evaluated for complete seismic assessment of the building. Nonstructural elements can generally be divided into architectural, mechanical, and electrical systems and components. In some cases it is observed that although the buildings have been able to demonstrate the required level of performance at the time of earthquake, malfunctioning of nonstructural components causes irreparable financial damages and casualties. Nonstructural components have two types of behavior in terms of performance: sensitive to displacement and acceleration. In this chapter the vulnerability assessment procedure of buildings, with regard to the performance of buildings, and the behavior of nonstructural components, in accordance with the requirements of Chapter 9 of Iranian seismic rehabilitation of existing building 360 and Chapter 11 of FEMA 356, are provided. Considering the performance of structures during earthquakes in recent decades, it Seismic Rehabilitation Methods for Existing Buildings. DOI: https://doi.org/10.1016/B978-0-12-819959-6.00004-X

© 2020 Elsevier Inc. All rights reserved.

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has been observed that the performance of nonstructural components plays an important role in postearthquake structure utilization. Nonstructural components include all components and contents of the building except the structural parts, that is, beams, columns, floors (ceiling), and in some cases walls. Common nonstructural components in buildings include: stepped ceilings, windows, office supplies, computers, shelves, drawer and interior items, heating equipment, refrigeration and ventilation equipment, electrical equipment, furniture, lights, and chandeliers (Fig. 4.1). For instance, a hospital that has to provide an operational occupancy at the time of earthquake cannot have a failure in stepped ceiling or a nonload-bearing wall collapse or it might happen in a residential building due to the lack of wall posts, wall is not involved with columns so it collapses during the earthquake and because of nonstructural nature of walls it causes severe damage. Nonstructural components are usually not analyzed by structural engineers, but architect, mechanical, electrical engineers, or interior designers determine their type and specifications. However, at the time of assessment and delivery of the seismic plan, seismic engineers can reduce the loss and damage of nonstructural components by retrofitting and rehabilitation of nonstructural components in the building (Fig. 4.2).

Figure 4.1 Structural stability and complete demolition of building facades in the lower floors in Kermanshah earthquake 2017.

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Figure 4.2 Evaluation of the destruction of a city’s vital arteries by earthquake.

Figure 4.3 Separation and fall of nonstructural components due to earthquake force.

4.1.1 The importance of damage to nonstructural components In understanding the subject, the first type of hazard is the wound or death of people due to injury or collapse of nonstructural components. Even seemingly safe objects can be dangerous and lethal in the event of a sudden collapse. For instance, in 1999 in Kocaeli, Turkey, an earthquake killed nearly 17,000 people and injured over 430,000. According to observations, nearly 50% of the injuries and 3% of the casualties were due to damage from nonstructural components (Fig. 4.3).

4.2 Understanding potential damage Inadequate bracing of the shelves, which at the time of the earthquake results in their overturning and may result in many casualties and

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financial losses. Lack of proper bracing of heating and cooling equipment and their plumbing, which can result in their damage during earthquake and may eventually cause great damage to structural elements. In many cases, failure in proper performance of electrical components during an earthquake can result in numerous fires and financial losses and casualties. At hospitals and other important centers, performance of electrical and telecommunication systems, as well as mechanical components, is of paramount importance so that these buildings should be seismically rehabilitated to meet the performance level of operational occupancy for nonstructural components because any damage to them may disrupt urban vital arteries. In all buildings, control of architectural components is required to control the damages. Imagine, for example, a hospital has a cantilever in entrance area that is seismically vulnerable to earthquakes, therefore during the earthquake, this cantilever member becomes unstable and eventually collapses at the entrance of the building (Fig. 4.4). The problem is that it disrupts the performance of one of the most important crisis management buildings at the time of crisis (Fig. 4.5).

Figure 4.4 Lack of proper bracing of important hospital equipment.

Figure 4.5 Long, unbraced cantilever roof at the main entrance to a hospital.

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All stepped ceilings must be examined thoroughly in terms of integrity and in case of possibility they also must be health monitored annually. Imagine that in a school or a residential complex, all the elements, structural and nonstructural, provide the expected performance level. There was a small water leakage in the ceiling that has caused decomposition of integrity/coherence elements of the stepped ceiling, therefore at the time of earthquake, stepped ceiling loses its statics and collapses and due to overcrowding and obstructions caused by elements at the time of evacuation can lead to lots of casualties (Fig. 4.6).

4.2.1 Assessing nonstructural components’ careful placement/layout In most of the cases it is observed that some electrical and mechanical components have been put concisely at the seismic contraction joint of the building and in the event of earthquake it leads to damage to these elements and some phenomena like firing and explosion in the building (Fig. 4.7).

Figure 4.6 Lack of proper restraint on nonstructural ceilings.

Figure 4.7 Proper layout and proper bracing of mechanical installations.

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Figure 4.8 Detach the facade from the wall, due to the lack of proper bracing.

It is important to control and examine the connection between wall and facade because at the time of earthquake there is a possibility of facade segments separation. Thus it is suggested that control of this section must be carried out with the highest precision (Fig. 4.8).

4.3 Rapid vulnerability assessment methods for nonstructural components An important question is that why nonstructural components must be retrofitted? The answer for this question is their characteristics and effects on seismic behavior of the buildings. This important issue affects: • Nonstructural components are more vulnerable than the main structure. • Being damaging even if the structure remains healthy. • Liability to cause considerable casualties. • Liability to cause serious secondary damages to the structure and its contents. • The ability to reduce or even stop the utilization capacity of the structure. • Discrediting seismic design and analysis.

4.3.1 Characteristics of nonstructural components • • •

Plenty of initial stiffness and low ultimate strength. Low accuracy or even discrediting the analysis. Causing early damage to the structure.

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Seismic rehabilitation of nonstructural components in buildings is done with respect to the target building seismic performance level and determining the seismicity. The process of seismicity assessment of nonstructural components in buildings consists of five main parts: • Complete visual inspection of nonstructural components of the building. • Behavior assessment to reach expected performance level of the studies. • Behavior performance of the nonstructural components on the structure must be controlled. • Classifying behavior of each nonstructural component. • Providing seismic design in case nonstructural components are vulnerable. In the following, each step of seismic assessment and rehabilitation of nonstructural components are explained.

4.3.2 Visual inspection Danger of nonstructural components is probable in any building, for example, house, office, workshop, kindergarten, school, shop, or asylum. Conducting building inspections leads residents to know more about the possible problems. Informing the landlords, managers, and residents of inspection results helps them to understand the current problems and evaluate the level of earthquake risk in nonstructural components of buildings. Experts can be used during building inspection in terms of abovementioned evaluation. There are often a lot of objects that are recognized dangerous in their current situation but their risk decrease by a simple displacement. By answering following questions these simple measures for decreasing hazards can be distinguished. • In which part of building do residents or employees spend most of their time? • Is there any heavy and unstable object near bed or tables that can be moved? • What is the extent of injuries in case of object collapse? • Which parts of the building have greater risk of safety in terms of time and the amount of occupation? • Are there any useless objects to be removed from the place? • Can some objects be displaced instead of being anchored to prevent probable injuries?

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If there is a possibility of slippage or collapse, in what direction will it move? Assessment structures in qualitative step are carried out based on: Building components configuration of different nonstructural components of building. Qualitative assessment of connections between structural and nonstructural components. Assessing physical problems of nonstructural components which are observed. Qualitative assessment of the extent of nonstructural components’ potential performance on behavior and performance of the building at the time of crisis.

4.3.3 Behavior assessment to reach expected performance level and assessment Assessment of nonstructural components in accordance with their general configuration in visual inspection should be specified based on the expected performance level set for the purpose of seismic rehabilitation of structural behavior. And its vulnerability must be analyzed quantitatively. This section includes the following steps: • Determining samples for a complete assessment. • Analyzing requirements of nonstructural components based on the target of building performance level. • Determining the behavior of every sample of nonstructural components. • Choosing the method of complete assessment. • Quantitative analysis of nonstructural components’ behavior. • Analyzing quantitative effect of nonstructural components’ behavior on structural components. • Providing a chart based on sample’s vulnerability and the undertaken configuration.

4.3.4 Determining samples for a complete and qualitative assessment One of the important points in assessing nonstructural components is determining the samples because inappropriate sampling may lead to different behavior from the assessed one at the time of earthquake. Regarding the availability of the detailed plans, the samples are divided into two groups.

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4.3.4.1 Availability of the plans • At least one sample of each nonstructural component. • In case of having accurate and flawless existing building plans, the sample can be used as the prototype for assessment. • In case of having flaw in existing building plan, at least 10% of components of each sample must be inspected visually. 4.3.4.2 Unavailability of the plans •At least three samples of each nonstructural component must be gathered and determined. •In case of similarity between results of samples’ behavior, they can be used as the prototype in assessment. •In case of discrepancy between behaviors of each nonstructural component sample, at least 20% of components of each sample must be inspected.

4.3.5 Checklist for nonstructural component hazards in earthquake 4.3.5.1 First part of checklist All nonstructural components of the studied building are listed, like following chart, by a group of experts to implement a proper method of rehabilitation through rigorous examination [1] (Table 4.1). Determining nonstructural components is one of the building official’s duties. The classification of nonstructural components studied in this chapter is presented in Table 4.2 [2,3]. 4.3.5.2 Second part of checklist This checklist is prepared to be used in inspecting the nonstructural components (electrical, mechanical, architectural, furniture, etc.) of the building and determining whether they are unsafe for residents or have probability of making financial damage or malfunctioning due to the effects of earthquake. Table 4.1 Form for sensitivity determination of vulnerability of nonstructural components. Building property Name: Date: Performance level: . . .. . .. . .. . .. . .

Row Nonstructural Position Number The Improvement component probability approach of risk Death Financial Disabling Designing Prescription damage damage Low risk, L; middle risk, M; high risk, H.

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Table 4.2 The breakdown of the nonstructural components discussed in this chapter. Architectural Furnishings and interior equipment

Exterior wall elements Partitions Interior veneers Ceilings Parapets and appendages Canopies and marquees Chimneys and stacks Stairs

Cabinet Flooring panel Elevators Conveyors

Mechanical equipment

Electrical and communications

Mechanical equipment

Electrical and communications equipment Electrical and communications distribution equipment Light fixtures

Storage vessels and water heaters High-pressure piping Fire suppression piping Fluid piping, not fire suppression Ductwork

The questions provided in this form are in a way that negative answer indicates probable danger for nonstructural component [1]. 4.3.5.2.1 Checklist of components of facilities

4.3.5.2.1.1 Emergency power generating equipment 1.Is power generator anchored properly? Especially if it is placed on the vibrating parting springs. 2.Are batteries connected to the carrier properly? 3.Is the carrier retained at both ends? 4.Is the carrier anchored to the concrete foundation by anchoring bolts? 5.Is the size of the concrete foundation big enough to prevent carrier from slippage or collapse? 6.Is the storage securely connected to its support? 7.Are supports of the storage retained at both ends? 8.Is the retaining connected to the concrete walls or foundation by anchoring bolts? 9.Is the size of the concrete foundation big enough to prevent storage from slippage or collapse?

Nonstructural components

565

10. Does the wall have sufficient strength to keep the fuel storage? 11. Are pipes of overflow section flexible enough to tolerate relative movements? 4.3.5.2.2 Electrical devices

1.Are convertors anchored to the wall or ground? 2.Are motor control centers properly anchored to the wall or ground? 3.Are electric levers properly anchored to the wall or ground? 4.Are electricity cables or wire carrying pipes flexible at connections or seismic joints? 5.Do the main or side cables’ routes have lateral anchors? 4.3.5.2.3 Fire communications and extinguish system includes all or parts of following equipment

1.Are smoke and fire alarm systems properly installed? 2.Is the controlling equipment related to fire communication or automatic doors system anchored correctly? 3.Is the fire extinguisher or extinguisher hose installed properly? 4.Is the fire extinguisher capsule fastened with a quick release belt? 5.Are different parts of sprinkler piping system laterally retained? 6.Is the stepped ceiling retained in a way that does not lead sprinkler to be broken? 7.Can pipes adapt themselves with relative movements at the seismic joints between buildings? 8.Is the extinguisher water pump anchored properly? Or vibrating parting springs and additional seismic constraints are used for that? 9.Is the water reservoir connected properly to its bases? 10.Are supports of the storage retained at both sides? 11.Are supports or retaining of storage anchored properly? 12.Are ventilators retained or anchored properly? 13.Are ventilator control centers anchored properly? 4.3.5.2.4 Liquid gas storage used in emergency power system, heating, or culinary

1.Is the storage securely connected to its supports? 2.Are legs of the storage retained at both sides?

566

Seismic Rehabilitation Methods for Existing Buildings

3.Are legs or retaining anchored to the ground or concrete foundation? 4.Is the size of foundation big enough to prevent storage from slippage or collapse? 5.Is there an automatic seismic shut-off valve in the system? 6.If the shut-off valve is manual, is the appropriate wrench placed beside it? 7.Do pipes have lateral retaining? 8.Do pipes have flexible connections at the joints to storage to provide ability of relative movements? 4.3.5.2.4.1 Piping system in building includes the following 1.Are water heaters or heating boilers securely anchored to the wall or ground? 2.Does the gas pipe have flexible connection to the water heater to provide ability of relative movements? 3.Is the water heater securely anchored to the wall or ground? 4.Are distributing pumps anchored or additional seismic constraints considered for them? 5.Are pipes retained in appropriate intervals? 6.Are connections of pipes to heating boilers or storages flexible? 7.Can pipes provide relative movements at the seismic joints in different parts of the building? 8.Are openings of the walls and other parts of building big enough for pipes to have relative movements? 9.Are pipes without asbestos isolation? (In terms of damaging asbestos fiber due to earthquake movements.) 4.3.5.2.4.2 Elevators following

and

escalators

generally

include

the

1.Does elevator’s cabin have appropriate connection with conductor rails? 2.Are cables installed in a way that do not dislocate at the time of earthquake? 3.Are counterbalances properly connected to the conductor rails? 4.Are connections between conductor rails and the building secure? 5.Are control motor and shelves anchored properly? 6.Are components of hydraulic system anchored properly?

Nonstructural components

567

7.Is the equipment of escalator anchored securely? 8.Is the control equipment related to moving corridors anchored properly? 4.3.5.2.4.3 Heating and air-conditioning system generally includes the following 1.Are heating boilers and furnaces anchored with proper bolts? 2.Are furnaces and heating boilers and furnace’s legs not made from unreinforced masonry? 3.Are chillers securely anchored or seismic parting springs and additional seismic constraints considered for them? 4.Are pumps or heating convertors secured or seismic parting springs and additional seismic constraints considered for them? 5.Are ventilators, blowers, and filters securely anchored or additional seismic constraints considered for them? 6.Are air compressors anchored or seismic parting springs and additional seismic constraints considered for them? 7.Are heating and air-conditioning units installed on the roof anchored or additional seismic constraints considered for them? 8.Are air-conditioning units installed securely on the walls or shelves? 9.Do hanging room heaters, especially gas-fueled ones, have lateral anchoring? 10.Do air channels have lateral anchoring? 11.Can air channels provide seismic movements at intersections with seismic joints? 12.Are the air-distributing gates retained over air channels or bound to the ties planning of stepped ceiling or wall? 13.Do the air-distributing gates have secure independent supports (e.g., at least two hanging strings for each gate)? 4.3.5.2.4.4 Minor mechanical machines 1.Is the brick chimney anchored to the roof? 2.Are chimneys anchored to the supports or foundation by anchoring bolts with appropriate length and double nuts? 3.Is the installed equipment on the roof anchored properly? 4.Are solar panels securely anchored on the roof? 5.Do the pipes have lateral anchoring?

568

Seismic Rehabilitation Methods for Existing Buildings

4.3.5.2.5 Checklist architectural components

4.3.5.2.5.1 Embedded partition wall 1.Is the partition wall reinforced? 2.Is the partition wall details in a way that it is possibly to slippage over them? 3.Is the partition wall half height retained to the upper structure? If the partition wall works as lateral supports? 4.Is the partition wall totally retained or anchored to the upper structure? 4.3.5.2.5.2 Stepped ceilings and soffit/intrados coverings 1.Do the suspended ties of stepped ceiling for retaining have enough diagonal wiring? 2.In panel stepped ceilings, do the panels have secure connections? 3.In coated stepped ceilings, is wire lath or plaster lathing securely connected to the upper structure? 4.Are coverings or tracery connected properly? Especially in places overlooking the exits. 5.Are wires or wooden fabrics beneath the coating connected properly to the upper structure? 4.3.5.2.5.3 Lightings 1.Are chandeliers or other hung objects equipped with safety rope to prevent them from colliding with each other or windows? 2.Do the hung or bar brace lamps have safety rope to prevent them from collapse in case of break of their bar? Or are they retained against oscillation? 3.Is the connection of single or rail lamp strong enough to stand against earthquake shakes? 4.Are emergency and exit lamps protected against collapse in their places? 4.3.5.2.5.4 Doors and exit paths 1.If the exit doors are made from fireproof heavy steel that may be blocked due to deformation in earthquake, is there a crowbar or a sledgehammer near them to make an emergency exit? 2.Do these doors have additional manual tools to be opened in case of blackout due to earthquake?

569

Nonstructural components

3.Do the steel staircase of tall buildings have a sliding bearing at any endpoints to adapt to relative displacement between floors? 4.Are unreinforced masonry walls around the ladder removed, reinforced, or confined? 5.Are piping, ducts, stepped ceilings, lamps, and other elements anchored properly against collapse? 6.Are furniture and other objects located in the exit path properly anchored to not collapse or make obstacle? 7.Are furniture and other unbraced objects far enough from exits that do not collapse or glide? 4.3.5.2.5.5 Windows 1.Do glasses have engineering seismic design to adapt to lateral movements of the building? 2.Are big glasses of shopping malls windows (especially front windows) made of safety glasses? 3.Are the frieze and doors made of safety glasses? 4.Are skylights made of safety glasses or protected by crash proof coating? 5.Are big glasses made of safety glass or do all the windows and glasses have engineering seismic design to adapt to environmental seismic displacement? 6.Are glass walls retained to main structure at the lateral length? 4.3.5.2.5.6 Accessories ornaments

and

permanent

interior

and

exterior

1.Are shelters reinforced and anchored properly? 2.Are other ornaments properly anchored to the building? 3.Are covering objects properly anchored to the building? 4.Do the cantilever walls or fences have engineering seismic design? 5.Are concrete block walls reinforced enough? 6.Do wall footings have enough strength against collapse at the time of earthquake? 7.Are hung accessories retained and protected by safety belt? 8.Does the lighting equipment of the area have proper support or is it securely connected to the building? 9.Are flagpoles securely connected to the building? 10.Are heavy or sharp statues anchored to prevent them from collapse at the time of earthquake?

570

Seismic Rehabilitation Methods for Existing Buildings

11.Are hung statues bound by safety belt to prevent them from collapse or severe oscillation? 12.Are traffic signs or advertising billboards outside of the building retained or anchored enough? 13.Are signs inside the building connected by joints? 14.Are clay pieces securely anchored to the ceiling? 4.3.5.2.6 Checklist furniture and interior content of building

4.3.5.2.6.1 Communication systems and emergency communication systems include the following 1.Is the radio equipment in the shelves or on the tables bound to prevent slippage and collapse? 2.Is the important equipment in the shelf or on the tables retrofitted to prevent slippage or collapse? 3.Do telephone machines have enough distance from the edges of tables or counters to prevent collapse due to glide? 4.Are public announcement systems braced to prevent slippage and collapse? 5.Are speakers installed at the height anchored to the structure or hung from safety belts? 6.Is the microwave equipment securely retained and anchored? 7.Is a backup of important computer information made and placed in a different location? 8.Is the important computer equipment securely anchored to their support? 9.Is sensitive computer or communication equipment located in a place away from sprinkler or its connections? 10.Are TVs and surveillance cameras installed on the walls or height anchored securely to seat? 11.Is the shelf or seat of the above-mentioned equipment properly connected to the wall or ceiling?

4.3.5.2.6.2 Office supplies and computer equipment 1.Are computers and their equipment that has a height more than two times of their width, securely anchored or retained?

Nonstructural components

571

2.Is the heavy computer equipment anchored to the structural floor slab and retained independent of stepped floor? 3.Are computer cables long enough to provide additional movements inside the building? 4.Are monitors anchored to the computer desk? 5.Are computers and printers anchored by proper constraints? 6.Are false floors retained by steel diagonal elements? 7.Do cable apertures on false floor have protective edges to prevent legs of equipment from gliding into them? 4.3.5.2.6.3 Document storage room 1.Are shelves anchored to floor, partition wall connection with ties or a solid wall by an angle? 2.Are constraints or elastic wires used at the shelf edge to prevent objects from falling off them? 3.Are books or other heavy big objects put in the lowest rows? 4.Is additional protection considered to prevent rare books from collapse or damage? 5.Are drawer locks or shelves doors secure? 6.Are tall cabinets fixed using one of following methods? a.Anchoring to a solid wall or partition wall connection with ties by angle. b.Anchoring to floor. c.Tying adjacent shelves to each other. 7.Is the location of unbraced shelves in a way that does not block the exit paths in case of collapse? 8.Are all tall shelves and closets securely connected to floor or wall? 9.Are heavy shelves or closets retained at both sides? 10.For closets that have a height more than width, are big anchoring bolts used to anchor each leg to the floor? 11.Are the breakable objects anchored to the shelf or closet or kept in resistant boxes? 12.Is the shelf placed in a safe accessible place to not damage a lot? 13.Is the shelf retained and anchored properly and its doors do have secure locks? 14.Are the breakable and valuable objects protected against collapse or falling from the shelf?

572

Seismic Rehabilitation Methods for Existing Buildings

4.3.5.2.6.4 Kitchen and laundry appliance. Usually, all or some of these appliances are in these places 1.Are these appliances securely anchored to the floor, wall, or counter? 2.Are gas and water pipes and connections able to adapt to seismic movements at the seismic joints or machine connecting part? 3.Are locks of closets and shelves secure? 4.Is the connection of the machine to floor or wall in a way that does not transfer heat to inflammable materials? 5.Is the chimney anchored to the heater? 6.Are chimney parts connected to each other firmly? 7.Is chimney anchored to the wall by a kind of thermal protector? 4.3.5.2.6.5 Hazardous materials 1.Are gas cylinders secured by chains on their both ends or another ways? 2.Are chains or retainers anchored to the wall or counter by nuts and bolts instead of being tied to the hook? 3.Are chemical containers kept in shelves with protective edges or put in drawers to prevent them from collapse in earthquake situation? 4.Are chemicals kept based on manufacturer’s instruction? 5.Are incompatible chemicals kept in an appropriate distance from each other? 6.Are chemical clearly listed and labeled in the shelves? 7.Are safety information documents kept in an appropriate distance from chemicals? 8.Are the shelves of hazardous materials securely connected to the floor or a firm wall? 9.Is asbestos isolation removed or put in protective cover to reduce possible damage? 4.3.5.2.6.6 Furniture and interior decoration 1.Are heavy vases in the shelves or niches secured against collapse? 2.Are the valuable things protected against collapse from niches? 3.Are partitions retained or set based on sustainable geometry? 4.Is the unbraced furniture placed somewhere that their collapse do not block the pathways or entrance rooms? 5.Are private or storing closets and autoselling machines anchored or placed away from exit paths?

Nonstructural components

573

4.4 Comprehensive assessment of vulnerabilities methods for analyzing nonstructural component There are two main methods to carry a comprehensive assessment: prescriptive method and analytical method that are discussed in the following sections.

4.4.1 Steps in nonstructural components analytical procedure •Determining the behavioral classification of the nonstructural components. •Determining the level of performance. •Calculating the horizontal and vertical seismic force (in case of need). •Calculating the seismic displacement or deformation (in case of need). •Criteria-based control of the stress or displacement or both of them due to the type of the nonstructural component.

4.4.2 Investigating requirements of nonstructural components rehabilitation based on the purpose of the study in building After sampling nonstructural components and determining their general configuration at the first part of complete vulnerability evaluation and based on following charts, it can be determined that whether nonstructural components are vulnerable with regards to the target of building seismic performance level? Or the studied nonstructural components do not need any rehabilitation?

4.4.3 Classification of nonstructural components according to their functional sensitivity According to FEMA 356 rules, nonstructural components of a building are classified in two main behavioral groups (Fig. 4.9): 1. Nonstructural components that are sensitive to acceleration The damage that is done to these components at the time of earthquake is due to applying loads and because these components are sensitive to inertia, they are called sensitive to acceleration. 2. Nonstructural components that are sensitive to deformation

574

Seismic Rehabilitation Methods for Existing Buildings

Figure 4.9 Classification of nonstructural components.

Figure 4.10 Evaluation procedure for nonstructural components.

These components are not only sensitive to inertia but they are also sensitive to relative displacement (story drift) of the structure at the time of earthquake.

4.4.4 Defining seismic load for the evaluation of nonstructural components We are authorized to calculate the seismic force for nonstructural components (Fig. 4.10). 4.4.4.1 Prescriptive procedure In this method, assessment of a unit is done with regards to the provided characteristics of the unit by the manufacturer. Using this method is welcomed only if the provided documents for the unit are from: 1. Creditable manufacturers. 2. Who are familiar with seismic issues? 4.4.4.2 Analytical procedure In this method, nonstructural components must be studied based on components’ behavior and also their forces, and deformations must be studied in accordance with provided charts in Section 4.4.2. Analytical method

575

Nonstructural components

which differs based on behavior of components and also the target of building seismic performance level will be discussed later.

4.4.5 Quantitative assessment of nonstructural components vulnerability If the behavior of nonstructural component determined as sensitive to acceleration, the imposed seismic design forces on it would be calculated by [2,3]: • For limited life safety level of performance (Table 4.3) Fp 5 1:6USsx UIp UWp -Fpv 5 •

2 3 Fp 3

(4.1)

For performance levels higher than life safety Seismic horizontal effective force
 0:4ap Ssx Ip Wp 1 1 2xh Fph 5 -Fph ðminÞ 5 0:3Ssx Ip Wp Rp

(4.2)

Seismic vertical effective force (Table 4.4) Fpv 5

0:27ap Ssx Ip Wp -Fpv ðminÞ 5 0:2Ssx Ip Wp Rp

(4.3)

And also, if the behavior of nonstructural components is recognized to be sensitive to deformation, the seismic design force applied to the Table 4.3 Quantitative assessment necessary parameters for life safety performance level. Parameter Description Equations

Fp Fpv Ss Ip Wp

Seismic design force applied horizontally to the center of mass of the component or distributed on the basis of the mass distribution of the component Seismic design force applied vertically to the center of mass of the component or distributed on the basis of the mass distribution of the component Spectral acceleration value at short periodic time for selected earthquake hazard level The relevant component performance coefficient which is 1 for the life safety level and 1.5 for the uninterrupted usability level Weight of component in operation mode

4.1

4.1

4.1 4.1

4.1

576

Seismic Rehabilitation Methods for Existing Buildings

Table 4.4 Quantitative assessment necessary parameters for higher than life safety performance level. Parameter Description Equations

ap x h Rp

Amplification factor for nonstructural component response Height of the center of mass of the component relative to the base of the building Average height of structure roof relative to base level Nonstructural component response modification factor

4.2, 4.3 4.2, 4.3 4.2, 4.3 4.2, 4.3

Table 4.5 Quantitative assessment necessary parameters for calculating deformation. Parameter Description Equations

Dp Dr X Y δxA δyA δxB

Relative seismic displacement Relative displacement ratio Height of upper support connection (x level) to base level Height of upper support connection (y level) to base level Relative displacement of building A at the x level, determined based on analytical relations Relative displacement of building A at the y level, determined based on analytical relations Relative displacement of building B at the x level, determined based on analytical relations

4.4, 4.4, 4.4, 4.4, 4.4,

4.5 4.5 4.5 4.5 4.5

4.4, 4.5 4.4, 4.5

nonstructural components is calculated according to the following relationships. 4.4.5.1 Calculating deformations Values of relative displacement (Dp) and relative displacement ratios (Dr) must be calculated by following equations. If the nonstructural component connects two points in levels of x and y in a building or a structural system, first equation, and if the nonstructural component connects two points of the same level in a building or a structural system, second equation, must be used (Table 4.5):
 δxA 2 δyA Dr 5 (4.4) ½X 2 Y  Dp 5 jδxA j 1 jδxB j We can extract values of ap and Rp from Tables 4.64.9 [2,3].

(4.5)

577

Nonstructural components

Table 4.6 ap and Rp for architected nonstructural components. Architectural Accept criteria

Exterior wall elements

Partitions element

Masonry material (like brick) Glass blocks Prefabricated panels Glazed exterior wall systems The other Heavy Light Glazed

Exterior veneers (facade)

Force and deformation control 1.0

1.5

Force and deformation 1.0 control/prescriptive Force and deformation control 1.0

2

Force and deformation 1.0 control/prescriptive Force and deformation control 1.0 Force and deformation control 1.0

3 2 2.5 1.5

4

Force and deformation control 1.0

3

Force and deformation control 1.0

3

Force and deformation 1.0 control/prescriptive Force and deformation 1.0 control/prescriptive Force and deformation control 1.25 Force and deformation control 1.0

2.5

1.0 1.5

Force and deformation control 1.0

1.5

Force and deformation control 1.0 Force and deformation 1.0 control/prescriptive Tile and ceramics Prescriptive 1.0 Directly applied to Force control 1.0 structure Dropped furred Force control 1.0 gypsum board Light panel Force control 1.0 Heavy panel Force control 1.0

1.5 2

Adhered veneer

Glazed veneers Joint components Gypsum board Stone, including marble Wood Glassed

Stepped ceiling

Rp

Force and deformation control 1.0 Force and deformation 1.0 control/prescriptive Force and deformation control 1.0

Anchored veneer for ductile material Prefabricated panels Glass blocks

Interior veneers (facade)

ap

3 2

2.5

1.5 1.5 1.5 2.5 1.5

(Continued)

578

Seismic Rehabilitation Methods for Existing Buildings

Table 4.6 (Continued) Architectural

Accept criteria

ap

Rp

Top brace

Force control

1.0

2.5

Bottom brace Top brace

Force control Force control

2.5 1.0

2.5 2.5

Bottom brace landing platform of stairs Arc slab of stair The other

Force control 2.5 Force and deformation control 1.0

2.5 3

Force and deformation control 1.0 Force and deformation control 1.0

3 3

Parapets and appendages Chimneys and stacks Stairs

Table 4.7 ap and Rp for Furniture and interior equipment nonstructural components. Furniture and interior equipment Accept criteria ap R p

Cabinet

Floor panel

Hazardous materials storage Computer access floors Computer and communication racks Bookcases Storage racks The others Any types

Elevators

Any types

Conveyors

Any types

Force control/prescriptive

2.5 1.0

Force control/prescriptive Force control/prescriptive

1.0 3.0 2.5 6.0

Force control/prescriptive Force control/prescriptive Force control/prescriptive Force and deformation control/prescriptive Force and deformation control/prescriptive Force and deformation control/prescriptive

1.0 2.5 2.5 2.5

3.0 4.0 4.0 3.0

1.0 3.0 2.5 3.0

4.5 Details of acceptance criteria for nonstructural based on seismic rehabilitation objective 4.5.1 Nonstructural components that are sensitive to deformation 4.5.1.1 Brickwork of interior partitions or partitioning In buildings, these nonstructural components are sensitive to deformation and like brickwork of exterior walls they must be able to tolerate out-of-plane

579

Nonstructural components

Table 4.8 ap and Rp for mechanical equipment nonstructural components. Mechanical equipment Accept criteria

Mechanical equipment

Cooling tower, held in alignment above its center of gravity Cooling tower, held in alignment below its center of gravity Boilers, furnaces, pumps, and chillers Accessories like radiators, fan coils, etc. HVAC equipment, vibrationisolated HVAC equipment, nonvibration-isolated HVAC equipment, mounted in-line with ductwork Storage vessels, Vessels on legs water heaters Flat bottom vessels

Piping

Fluid piping fire suppression High pressure

Hazard materials Nonhazard materials Ductwork

ap

Rp

Force control

1.0 3.0

Force control

2.5 3.0

Force control

1.0 3.0

Force control

1.0 3.0

Force control

2.5 3.0

Force control

1.0 3.0

Prescriptive

1.0 3.0

Force control/ prescriptive Force and deformation control/prescriptive Prescriptive Force and deformation control/prescriptive Prescriptive Prescriptive Prescriptive

2.5 1.5 2.5 3.0

2.5 4.0 2.5 4.0

2.5 1.0 2.5 4.0 1.0 3.0

Table 4.9 ap and Rp for electrical and communications nonstructural components. Electrical and communications Accept criteria ap R p

Electrical and communications equipment Electrical and communications distribution equipment Light fixtures

Any types

Force control

1.0 3.0

Any types

Prescriptive

2.5 5

Recessed Surface mounted Integrated ceiling and pendant Lighting systems

Prescriptive Prescriptive Force control/ prescriptive Prescriptive

1.0 1.5 1.0 1.5 1.0 1.5 1.0 1.5

580

Seismic Rehabilitation Methods for Existing Buildings

force. In accordance with their level of performance, acceptance criteria in these components are divided into two groups: 1. In life safety, they must be able to tolerate out-of-plane forces and also the calculated relevant displacement for this partition wall must not be more than 0.015. 2. In immediate occupancy, they must be able to tolerate out-of-plane forces and also the calculated relevant displacement for this partition wall must not be more than 0.01. 4.5.1.2 Finishing the walls, exterior walls, facade By facade we mean all kinds of it including bond, sewn façade, and prefabricated panels. The facade that is bond on exterior partitions by masonry, concrete, cement coat, and the facade sewn on partitions by brickwork and stoneware has a behavior sensitive to deformation. In accordance with their level of performance, acceptance criteria in these components are divided into two groups: 1. In life safety, they must be able to tolerate calculated forces and also the calculated relevant displacement for this facade must not be more than 0.02. 2. In immediate occupancy, they must be able to tolerate calculated forces and also the calculated relevant displacement for this facade must not be more than 0.01. 4.5.1.3 Decorative stones, wood, and interior mirrors All the decorative stones, wood, and interior mirrors, whose frames are more than 120 cm from the base level, have deformation-sensitive behavior. If decorative stones and mirrors are properly connected to the wall, their acceptance criteria are like that of the exterior facade. Also in case of wood, for performance level of life safety there is not any need for rehabilitation control and like exterior facade, only in immediate occupancy the acceptance criteria are applied. 4.5.1.4 Staircase In assessing nonstructural components of staircase all components including deck, landing, and handrails are to be studied. These components are sensitive to deformation, and their acceptance criteria are in a way that in performance level of life safety and immediate occupancy they must not only control relative displacement but must be able to tolerate calculated sensitive forces.

Nonstructural components

581

4.5.1.5 Equipment conveyors In assessing nonstructural components, these components are sensitive to deformation and their acceptance criteria are in a way that performance level of life safety does not need any rehabilitation but in terms of immediate occupancy they not only must control relative displacement but also must be able to tolerate calculated sensitive forces.

4.5.2 Nonstructural components that are sensitive to acceleration 4.5.2.1 Stepped ceiling In buildings with sloped roofs, generally stepped ceilings, which are hung to main components of the ceiling, are used. In some cases these ceilings have independent connections. Behavior of this nonstructural component is sensitive to acceleration. Some types of this ceiling are plaster and soil coated by lath and covering by light or heavy panels. Acceptance criteria for these kinds of ceilings in performance level of life safety and immediate occupancy must be in a way that their frame and cover be able to tolerate calculated forces. 4.5.2.2 Shelters, sides, and chimneys These are nonstructural components that only in following situations are needed to be controlled in terms of rehabilitation. Behavior of these components are sensitive to acceleration, and acceptance criteria for these kind of components must be in a way that their frame and cover be able to tolerate calculated forces in both performance level of life safety and immediate occupancy. Using proscriptive method in building chimneys is possible. 1. In reinforced masonry h/t . 15 and in unreinforced masonry h/t . 3. 2. For sides that are made of unreinforced masonry like brick and stone. 3. Self-supporting chimneys that are installed on the roofs (Fig. 4.11). 4.5.2.3 Stepped (false) floors These floors are used in buildings with infrastructural equipment. Behavior of these nonstructural components are sensitive to acceleration, and their acceptance criteria must be in a way that performance level of life safety does not need any seismic rehabilitation and only they must be able to tolerate calculated forces in performance level of immediate occupancy.

582

Seismic Rehabilitation Methods for Existing Buildings

Figure 4.11 Parapet wall separating due to earthquake force.

Figure 4.12 Proper implementation of powerhouse.

4.5.2.4 Thermal and cooling installations This part includes all thermal and cooling installations except liquid reservoirs, water heaters, and pipes. These installations are sensitive to acceleration, and in performance level of life safety and immediate occupancy they must be able to control calculated forces. Also if the nonstructural components of this section are among below, they need rehabilitation control. 1. Unbraced equipment heavier than 45 kg must be controlled to have overturning moment with safety factor of 15. 2. Equipment heavier than 10 kg must have a proper support at floor or ceiling. 3. Weigh more than 180 kg. 4. Central machines of engine room, including boilers or furnaces, cooling towers, and small equipment (Fig. 4.12). 4.5.2.5 Liquid reservoirs and water heaters These acceleration-sensitive components must be analytically evaluated and rehabilitated if their storage volume is more than 400 L. Their

Nonstructural components

583

acceptance criteria also must be in a way that in performance level of life safety and immediate occupancy they could tolerate calculated forces. In case their storage capacity and volume is less than 400 L, prescriptive methods can be used. 4.5.2.6 Pipes and their connections All the pipes, including those that contain hazardous materials, underpressure piping, and piping without any pressure, are sensitive to acceleration. Also, their acceptance criteria are in a way that in performance level of life safety and immediate occupancy, their supports and anchoring must be able to tolerate the calculated forces. It is worth mentioning that in all cases if the pipes cross the separation joints in floors, they must be controlled in terms of displacement. 4.5.2.7 Electrical and telecommunication equipment All electrical and telecommunication equipment that fall into following parameters need to be controlled in terms of rehabilitation. These installations are sensitive to acceleration, and they must be able to tolerate calculated forces in performance level of life safety and immediate occupancy. In most cases, using prescriptive method is permissible for them. 1. Their unbraced equipment heavier than 45 kg must be controlled to have overturning moment with safety factor of 15. 2. Equipment heavier than 10 kg must have a proper support at floor or ceiling. 3. Weigh more than 180 kg. 4.5.2.8 Shelves According to the classification of seismic rehabilitation instruction for existing buildings, shelves are divided into four main categories: • shelves of hazardous materials; • shelves of telecommunication and computer equipment; • bookshelves; and • shelves of other objects. This kind of nonstructural components is sensitive to acceleration and in performance level of safety and immediate occupancy, use of prescriptive method is permissible for them. For second category of shelves, using prescriptive methods is allowed.

584

Seismic Rehabilitation Methods for Existing Buildings

4.5.2.9 Elevator In elevators, nonstructural components have two behaviors. All components of elevator are sensitive to acceleration, and only lifting rails and cabin that continue in story height are sensitive to deformation. Performance level of safety and immediate occupancy of these components must be in a way that all of the elevator components must be able to tolerate calculated forces. The calculated displacement for lifting rails and cabin must be controlled. Using prescriptive methods is also permitted for this case.

4.6 Common methods for seismic rehabilitation and reducing danger of nonstructural components There are different methods to reduce probable risks that are caused by earthquake to nonstructural components. These methods range from simple steps based on common detection to complicated specialized measures. Simple steps include changing the location of heavy anchorage furniture near the corridors, doors, and beds as well as implementing some of the simple retrofitting details provided in this instruction. In large organizations with complex buildings, qualified consultants are required to design the engineering details necessary for the buildings and architectural elements of buildings. In places such as hospitals, museums, libraries, laboratories, and industrial buildings, there is usually special furniture and equipment that should be used, and qualified consultants are needed to design the details appropriate for their placement. Existing measures are not usually complex methods, so that, most of the time, the original nature of the nonstructural member does not change and the solutions are for consolidation. These solutions fall into two categories: traditional and modern. The traditional way is to either repair or retrofit the component itself or retrofitting or adding braces or connections to the structure. In these methods, the quantity of destruction operation is low, so they are appropriate measures, however, if the traditional method of “replacing a nonrehabilitation component with an appropriate component” is used, the demolition rate is high and it is not recommended and in many cases. Modern methods include the use of seismic isolation systems. This type of seismic rehabilitation is more used for heavy objects or for rehabilitation of nonstructural components in important buildings, such as hospitals, telecommunication centers, and power plants [1,4,5] (Fig. 4.13).

Nonstructural components

585

Figure 4.13 Seismic rehabilitation of the parapet walls method.

Two categories of seismic rehabilitation of nonstructural components are: • Retrofitting the component itself or adding braces or connections to the structure and replacing the nonrehabilitation component with the appropriate one. • Seismic isolation systems. Below are examples of seismic rehabilitation systems for nonstructural components with explanations. • Seismic rehabilitation of the parapet walls and pipes of the ceiling which has a cantilever function is in a way that the mass and stiffness of the ceiling are used to rehabilitate performance by making a connection between the free pipes or the wall and the ceiling. In designing connections of nonstructural components to the support, the earthquake horizontal force is considered as a percentage of the weight of the member. What is specifically addressed in earthquake codes is only the effects of earthquake inertia forces on nonstructural components. However, the effects of building deformation and separation joints between the buildings should also be considered in the seismic design of nonstructural components. • For seismic rehabilitation of thermal and cooling installations, we can use the below sample method (Fig. 4.14). • Bracing of mechanical and quasimechanical components. In this case, prevention of movement is done by stabilization (Fig. 4.15). This type of rehabilitation is mostly done in hospitals, laboratories, factories, and kitchens. • An example of rehabilitation by making link between lightweight elements to increase weight and statics. In this method, lightweight shelves are connected to each other by some elements and increase statics of nonstructural component by connecting to an element with considerable weight (Fig. 4.16).

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Figure 4.14 Seismic rehabilitation of thermal and cooling installations.

Figure 4.15 Bracing of mechanical and quasimechanical components.

Figure 4.16 Rehabilitation by making link between lightweight elements.

A.1 Case study examples A.1.1 Examples of seismic rehabilitation and the evaluationbearing capacity of nonstructural components A building has been constructed in an area with high seismic risk, and its structural components have been seismically rehabilitated. To meet the

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target of building seismic performance level, the assessment and seismic rehabilitation of its nonstructural components shall also be carried out. Based on visual inspections, the effective nonstructural components of this building are partition wall and shelves of network servers and printers. What is the method of seismic assessment and rehabilitation for seismic rehabilitation of these components (Fig. A.1)? The first step is to extract behavioral classifications based on tables presented in this section or in FEMA 356 publications or 360 journal (Table A.1). Step two: quantitative evaluation of nonstructural components. As it is extracted from the provided tables, the partition wall in this project is sensitive to acceleration, and shelves and printers are sensitive to displacement. At first, the effective weight of each component is determined. This parameter for partition wall, shelves, and printers is, respectively, WP1 5 5456 (kg), 130 kg, and 20 kg. Partition wall (sensitive to deformation). ap 5 1:0; Rp 5 3:0; Ss 5 0:75; Ip 5 1:0; WP1 5 5465 ðkgÞ  0:4 3 1:0 3 0:75 3 1:0 3 5465 1 1

ð2 3 8:325Þ 10:2



FP1 5 3 5 1438:58 ðkgÞ-1438:58 ðkgÞ # 1:6 3 0:75 3 1:0 3 5465 5 6558 ðkgÞ

Figure A.1 Some of the impact of earthquake force on nonstructural components.

Table A.1 Assessed nonstructural components of the building. Behavioral Amplification Modification factor classifications factor,ap of response,Rp

Partition wall Shelves Printer

Deformation Acceleration Acceleration

1 1 1

3 3 3

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0:27 3 1:0 3 0:75 3 1:0 3 5465 3 2 5 368:89 ðkgÞ # 3 704:56 5 469:71 ðkgÞ 3

FPV1 5

h1 5 2:95 ðmÞ; L1 5 3:25 ðmÞ; t1 5 0:05 ðmÞ ! kg qp1 5 570 ; WP1 5 5465 ðkgÞ; Fp1 5 1438:58 ðkgÞ m2 M1 5

FP1 3 L 1438:58 3 3:25 5 5 1168:85 ðkg mÞ 4 4

  ht 2 2:95 3 ð0:11Þ2 5 5 0:0059 m3 6 6 8 ! > kg > > σ1 . σc 5 4 >  > < cm2 M1 kg 5 19:81 σ1 5 > S1 cm2 > > > > : σ1 f σt 5 0:15 3 4 5 0:6 S1 5

! kg cm2

According to the results, it is obvious that because of compressive and tensile stresses the partition wall is ill-conditioned and the imposed stress exceeds the capacity of this member and this nonstructural component becomes vulnerable against the imposed load. Shelves of computer and network servers (sensitive to acceleration) h 5 2 ðmÞ; FP 5 156 ðkgÞ FP 5 1:6 3 0:75 3 1:0 3 130 5 156 ðkgÞ-FPV 5

2 3 156 5 104 ðkgÞ 3

MOTX 5 MOTY 5 FP 3 h 5 156 3 2 5 312 ðkgÞ MSTX 5 104 3 0:4 5 41:6 ðkgÞ 0M

MSTY 5 104 3 0:25 5 26 ðkgÞ OTX

# C1 C2 C3 J-7:5 . 1:0 3 1:0 3 1 3 2 5 2:0 ðNot OKÞ

1

C B MSTX C B C B A @ MOTY # C1 C2 C3 J-12 . 1:0875 3 1:0 3 1 3 2 5 2:175 ðNot OKÞ MSTY

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Figure A.2 Seismic rehabilitation method.

Printers h 5 0:6 ðmÞ; FP 5 24 ðkgÞ FP 5 1:6 3 0:75 3 1:0 3 20 5 24 ðkgÞ-FPV 5

2 3 24 5 16 ðkgÞ 3

MOTX 5 MOTY 5 FP 3 h 5 24 3 0:6 5 14:4 ðkgÞ MSTX 5 16 3 0:2 5 3:2 ðkgÞ MSTY 5 16 3 0:2 5 3:2 ðkgÞ MOTX # C1 C2 C3 J-4:5 . 1:0 3 1:0 3 1 3 2 5 1:2 ðNot OKÞ MSTX MOTY # C1 C2 C3 J-4:5 . 1:0 3 1:0 3 1 3 2 5 1:2 ðNot OKÞ MSTY According to the results (overturning moment control), it is clear that the investigated shelf is vulnerable to lateral load, and screw connections with proper strength and arrangement to the curtain wall can be used to bracing and controlling collapse (Fig. A.2).

A.1.2 How to develop a nonstructural component behavior algorithm in a building using clinical therapy? The building of a therapeutic clinic was assessed to meet a specific target of building performance level, and the structure of the building turned out to be capable of responding to threats based on expected performance at the time of the earthquake. To provide a comprehensive immediate

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occupation and to prevent the overall performance of the building from falling down, the algorithm of nonstructural components vulnerability assessment was prepared as follows and finally the nonstructural components were assessed. At first, a comprehensive prioritization for earthquake threat should be set for the building. In this regard, as you know, the building or training center has a comprehensive health system that should function at the level of performance when an earthquake strikes. This system consists of human

Figure A.3 Algorithm for evaluation of nonstructural in a hospital.

Table A.2 Divided nonstructural components. Architectural Equipment

Interior partitions Facades Suspended ceilings Roofs or decks Parapets Chimneys Plaster Glass windows Attachments (signs, antennae, etc.) Ornaments Canopies Lighting system Railings Doors and exit routes Expansion joints

Medical equipment Laboratory equipment Industrial equipment Furniture Supplies

Basic installations

Medical gas piping Industrial gas piping Vacuum devices Steam Air-conditioning systems Heating Ventilation Electrical wiring Backup power Communications Drinking water Industrial water Sewerage Fire sprinklers Other pipelines Circulation: elevators, stairs

Nonstructural components

591

and physical, each of which consists of special sections directly connected to the renderable services section. These services are directly related to the main performance of the building, which is an important indicator of maintenance. The ultimate demand is the performance that covers all of this (Fig. A.3). Table A.2 shows a breakdown for nonstructural components in a hospital unit.

References [1] Tehran Disaster Mitigation and Management Organization (2009), A Practical Guide to Reduce Risks of Non-Structural Building's Elements in Earthquake. [2] American Federal Emergency Management Agency (FEMA) (356), Prestandard and Commentary for the Seismic Rehabilitation of Buildings. [3] Islamic Republic Vice Presidency for Strategic Planning and Supervision Office of Deputy for Strategic Supervision, Department of Technical Affairs, Code. No (360) First Revision, Instruction for Seismic Rehabilitation of Existing Buildings. [4] Federal Emergency Management Agency (FEMA) (1997), NEHRP Commentary on the Guidelines for the Seismic Rehabilitation of Buildings (FEMA 274), Reston, VA. [5] Federal Emergency Management Agency (1994), Reducing the Risks of Nonstructural Earthquake Damage, FEMA 74.

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Chapter at the glance

CHAPTER FIVE

Site pathology and seismic rehabilitation methods Aims By reading this chapter, you are introduced to: • • • • •

learning about the effects of the site on earthquake damage; getting acquainted with quick and detailed assessment techniques; preparing the reader's mind for modeling presenting site and soil rehabilitation plans; providing practical approaches to the site improvement process; and understanding the concepts of the chapter by providing two practical examples;

5.1 Introduction to site effectivity in building performance levels Earthquake waves are undergoing changes as they move away from the earthquake focus and pass through alluvial layers. The factors related to the distance from the earthquake focus are known as “track impact” and the factors associated with the alluvial layers on the bedrock are known as “site effects.” The effects of the site are manifested by the intensification of earthquake waves and changes in the characteristics of seismic waves such as amplitude, frequency, and durability of the strong movement. For example, on 19 September 1985, an earthquake measuring 8.1 on the Richter scale occurred in Mexico, although it caused moderate damage at its center (Pacific coast) but sustained severe damage at 350 km in Mexico City. Following an earthquake, 12 November 2017 at Sarpol-e-Zahab in Kermanshah and dispatching various expert groups to evaluate different aspects of this earthquake, it was observed that the distribution of damages in this area was not uniform and varied significantly in different parts of the city even with the type of structures. Two distinct demolition trends were seen in the city. For example, at the western end of the city, toward the Ghasr-e-shirin at the foot of the mountain slopes to the river, two sets of MEHR housing complexes, one in the vicinity of the stone elevation and the other in the slope. The proximity of the built river had shown quite Seismic Rehabilitation Methods for Existing Buildings. DOI: https://doi.org/10.1016/B978-0-12-819959-6.00005-1

© 2020 Elsevier Inc. All rights reserved.

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Figure 5.1 An image of site effects in the Kermanshah earthquake 2017.

different behaviors. The complex adjacent to the river was heavily damaged by structural components and severely damaged by nonstructural components, while the other complex was slightly damaged without structural damage and nonstructural damage. In this regard, the study of geotechnical hazards is an essential issue in seismic recovery operations (Fig. 5.1).

5.1.1 Determination of site properties The information needed to determine and evaluate structural features is divided into two main groups: foundation information and site hazards. According to the following algorithm, other required features are provided. The following is a description of each of the items listed (Figs. 5.2 and 5.3).

5.1.2 Impact of the site on earthquake Unfortunately, in local the country’s seismic and geotechnical bylaws, there are brief references to the enormous impacts of the site's impact on changing bed behavior. Based solely on the average of the mechanical properties of the alluvial layers, bed behavior has been incorporated into several different soil types. During earthquake, the energy accumulated in the focal area is released in the form of seismic waves and alluviums with different structures have different responses. Research has also shown that responses to different earthquakes at different stations are different because the characteristics of the sites vary. Also for different earthquakes a building shows almost the same mapping. The geological characteristic of the site is the most important factor affecting seismic responses, for example, when the structure of the environment is in horizontal layers, only volumetric waves moving up and down in the surface layers are trapped. But when the two- or

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Figure 5.2 Monitoring the site properties.

Figure 5.3 Scheme of the site threat at a glance. Source: From https://commons.wikimedia.org/wiki/Main_Page

three-dimensional structure, that is, lateral heterogeneity, also exists, the surface waves created by this dissonance are also trapped. The interference between these waves results in an intensified phenomenon whose shape and frequency depend on the geometrical and mechanical properties of the structure in question. The main parameters that are effective in identifying the structure are the geometry of the layers (thickness and discontinuity of the layers), topographic shape, physical, dynamic, and mechanical properties of the rock materials, and soil properties. The results of various studies indicate that, in general, softer soils have a larger reinforcement function. It should be noted, however, that in the

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case of a soil having a high special stiffness whose natural frequency is the same as that of the bedrock, the preceding sentence is not true and this hard soil is harder to obtain a larger reinforcement function. In this case, the above-mentioned soil is exacerbated and the shaking time at ground level is usually longer than that of bedrock, which is proportional to the amount of soil softness and thickness. Studies of different earthquakes have confirmed that shaking time has a major role in the rate of damage due to liquefaction and in this respect it can be said that the rate of damage in soft soil is more than damage on hard soil. According to research using computer simulation software, soil stratification close to the surface has a significant impact on amplification or weakening earthquake forces. Keep in mind that in the soil of the construction site, with the changes made in the layers close to the earth's surface and its change from sand to clay, the response curve of the earth's motion intensifies, due to the less dampness of the soft soil. This is evident in the curve in Fig. 5.4 (diagram (a) hard layer) Also by increasing the soil thickness by two times, assuming the coarsegrained soil near the surface, it was observed that the movement on the surface is weakened; this can be explained by increasing the thickness of the soil depleting layers (gravel and sand). The wave of the earthquake decreases until it reaches the earth's surface, and we see a decrease in amplification ratio of earthquake. Another comparison was made with changes in the acceleration of the earthquake inlet. Earthquake inlet acceleration changes affect ground response. Thus, as the input acceleration decreases, the ground response intensifies. Mild earthquakes have more amplification ratio than strong earthquakes. To justify this, the damp factor can be attributed, as in small earthquakes, small strains are created, and in small strains, little damp is activated, but in large earthquakes, large strains are created that produce large damp and reduces ground motion. This is evident in the curve in Fig. 5.4 (diagram (b) acceleration).

Figure 5.4 Diagram of soil behavior on seismic waves.

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Finally, as a cases study, a comparison of the types of soils is provided in Iranian earthquake Code 2800. For Sarpol-e-Zahab, by decreasing shear wave velocity and in other words, soil softening, responses at low frequencies have more amplification ratio, because at low frequencies, small strains are created, and at low strains, little attenuation is activated and earthquake motion. The ratio of inlet movement to bedrock increases. This is evident in the curve in Fig. 5.4 (diagram (c) soil type). It has been observed that in a particular earthquake such as Kermanshah in a small town such as West Islamabad, extensive devastation has occurred in some areas and minor devastation elsewhere, implying the importance of the site's local impacts. According to the responses obtained from computer simulation analyzes, the following results were obtained: • An earthquake can be aggravated or attenuated at certain frequencies depending on soil characteristics. • By changing the soil profile close to the ground surface, the response curve of the ground motion spectrum changes due to differences in the damp of different soils. • Mild earthquakes are more aggravating than strong earthquakes and are more dangerous. Because the earthquake inlet acceleration changes the ground response and decreases the input acceleration which increases the response at the ground level. • Gravel soils generally have higher initial hardness than sand. Sand also has a higher initial hardness than clay. As a result, the damping of gravel and sand is greater than clayey soils.

5.1.3 Rational behind seismic rehabilitation of the site The philosophy behind seismic rehabilitation of site starts with following question. Why and when do we rehabilitate foundation site? If the geotechnical conditions of ground are not appropriate for constructing any types of structures, it is necessary to: • change the place of project; • replace imperfect natural materials with perfect ones; • carry out perfect design of this situation (floating foundations, deep foundation, etc.); and • rehabilitate the existing soil. Annually, considerable amount of money is spent to construct foundation in weak and imperfect grounds. Using rehabilitation methods leads to considerable reduction in time and expense of projects.

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5.2 Understanding the potential damage of site treatment Considering the topography of some areas, it is necessary to study and evaluate the structures on the slope ground. Therefore, the stabilization of trenches is very important depending on their condition. The origin of these instabilities can be generally attributed to the material (shear strength), weathering and alteration of rock properties (tuff rocks), and the change in layering. It is necessary to study the exact cause of instability in each section carefully and according to geotechnical and geometrical conditions, a suitable plan should be presented. Based on local surveys and surveys, the problems related to the stabilization of structural trenches can be summarized as in the following sections.

5.2.1 Instability of downstream trenches of buildings This phenomenon is due to the high slope of some areas and considering the geometrical dimensions of existing buildings, proximity of buildings, steep slopes of high altitude, which need to be stabilized. These instabilities will be problematic during construction and operation (Fig. 5.5).

5.2.2 Instability of trenches under building’s foundation This is unavoidable due to the location constraints of existing buildings and the location of adjacent buildings on either side of the slope ground crown with stone and soil. In these conditions, high siting and general instability under the buildings were very likely, thus making the operation of buildings difficult (Fig. 5.6).

Figure 5.5 Instability of downstream trenches of buildings.

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Figure 5.6 Instability of trenches under buildings.

Figure 5.7 Trench instability of access roads.

5.2.3 Trench instability of access roads Trenches adjacent to the access roads should also be adequately protected to maintain operating conditions. The instability that has occurred is mainly due to the low resistivity properties of the soil and rock layers, weathering of the layers, and change of layering, examples of which are shown in Fig. 5.7.

5.2.4 Problems with soil foundation capacity modification under foundation Aggregates with different parameters of bearing capacity and low strength, cause problems of sitting and bearing capacity instability. In the other case, the presence of soil materials near the rock layers, as well as the hardness of the adjacent rock layers in the subfoundation area, is the major

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cause of problems with subsoil-bearing capacity. It is important for us to know the maximum bearing capacity of soils because the sum of all structural loads will eventually have to be transferred to the soil on which the structure is built. Soil-bearing capacity is the maximum load that can be applied per unit area of the soil without any breakage in the soil. For seismic, rehabilitation of existing foundation structures should take into account the maximum soil-bearing capacity. Occasionally, existing settlement in buildings may indicate a lower soil load capacity under the foundation, which should be appropriately improved.

5.2.5 Soil liquefaction Soil liquefaction is a phenomenon that often occurs in small to medium sands. In sandy soils, sand particles are retained by bonding between particles and the force can be transmitted through these joints. During lubrication, these joints break down and the force between them becomes cavity pressure and the soil shear strength becomes zero. Sandy soil behaves like a liquid whose specific gravity equals saturated soil. The main mechanism of liquefaction in saturated and loose sand layers is the gradual increase of pore water pressure due to cyclic stresses caused by earthquake shear wave propagation. If the sand is sufficiently loose and the loading intensity large enough, the pore pressure may be equivalent to the effective stress between the particles. At this moment, the forces between the particles disappear and the particles become suspended and submerged. In such circumstances, the soil of the site should be appropriately seismically improved

5.2.6 Damages that lead to the rehabilitation of the subsoil • • • • • • • •

Lifting force Instability of the structural site, especially for buildings on sloping ground Insufficient flexural and shear capacity of the foundation section Invasion of harmful chemicals in soil and groundwater into concrete Insufficient lateral resistance to withstand the forces applied to the foundation of the building Apply more compressive or tensile force to the pile Creating many unacceptable meetings under the foundation of the building Liquefaction potential of sand

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5.3 One method of rapid vulnerability for soilbearing capacity 5.3.1 What is the safe bearing capacity of soil? This field experiment is designed to investigate the capacity of soil to resist loads. For example, consider a small plastic chair, made for children and with a carrying capacity of (10 kg) 22 lbs, suppose an adult sits on that chair, the chair will fail. The same applies to the soil, if the soil becomes fractured and settles if the soil exceeds the load capacity. To avoid this, the safe bearing capacity of the soil is calculated, which is done for the various parts of the structure and its foundation. Most of the time the unit area of the soil can tolerate without any deformation and settlement is considered as safe soil-bearing capacity (Fig. 5.8).

5.3.2 How to calculate safe soil-bearing capacity? Soil safety handling capacity 5

Final soil-loading capacity (5.1) Cross-sectional area 3 Confidence factor

5.3.3 Final soil-bearing capacity Where the soil begins to move and changes, it is named after the soil's ultimate bearing capacity (Fig. 5.9). For example, consider a rubber cushion that is pulled in two opposite directions, as long as it is able to return to its original state, with its elastic properties. If the cache is stretched too much it will break. The reason

Figure 5.8 Effectivity of filling soil under the foundation.

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Figure 5.9 Effectivity of filling soil under the foundation.

for the rupture is that the cache has lost its elasticity properties and is no longer able to return to its original state. The same is true for soil, when the load on the soil exceeds a certain limit, the soil is in the final capacity. After this step, the soil begins to settle, this point is known as the ultimate bearing capacity of the soil. The ultimate bearing capacity varies for different types of soils, depending on the weather and climate. Depending on the conditions and type of numerical construction, the confidence factor is considered to be between 2 and 3. For tall builders, this number is 3.

5.3.4 Procedures for testing determination of safe soilbearing capacity by rapid in situ method There are many theories that each has somehow explained the method of calculating the safe soil-bearing capacity, all of which are considered the most convenient and reliable experiments on falling weights on the soil.

5.3.5 Weight loss method This method is used to determine the soil-bearing capacity. First, drill a hole to the required depth (preferably the same depth as the foundation depth). Next, take a cubic weight of the specified weight and dimensions and drop the weight from a certain height on the drilled holes. Then, measure the effect of the weight falling on the soil. To obtain more accurate results, weights must be dropped several times in the same pit and the depth (d) taken from all of them.

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5.3.6 Example If the weight is 0.6 kg and its fall height is 120 cm, the average depth is 0.8 cm, the cross section is 20 cm, and the confidence factor is 2, the amount of safe soil-bearing capacity can be calculated as follows: Final bearing capacity-ð0:6 3 120Þ=0:8 5 90 kg Soil safety bearing capacity-ð90=20 3 2Þ 5 2:25 kg=cm2 The values in Table 5.1 are suitable for preliminary design. The exact bearing capacity of each type of soil should be calculated in accordance with regulatory procedures (Fig. 5.10). Table 5.1 Soil safety bearing capacity for Eq. (5.1). Row Soil type Soil safety bearing capacity (kg=cm2 )

1 2 3 4 5 6 7 8 9 10

Soft and wet clay Dark organic soil Loose sand (nondense) Clay—high density Soft stone Sand—high density Hard rock Sand with coarse aggregate Medium-grained sand Sand with fine grading

Figure 5.10 Soil safety bearing capacity.

0.5 1.5 2.5 4.5 4.5 4.5 3.3 4.4 2.45 4.45

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5.4 Comprehensive assessment of vulnerabilities for defining soil-bearing capacity 5.4.1 Methods for computer modeling of site component capacity Evaluation of soil-bearing capacity coefficients following earthquake loads has always been of interest to various researchers under the earthquake. In all the studies and analyzes, earthquake loads have been considered in various ways with quasistatic performance and have produced different results. In this regard, the evaluation of soil load capacity coefficients under earthquake loads has been performed using limited components software such as PLAXIS and the results have been evaluated and compared with the results presented by other researchers. In addition, the effect of inertial soil mass inertia on soil-bearing capacity coefficients in quasistatic modeling was numerically modeled and compared with other researchers. On the other hand, considering the inertial effect of subsoil mass inertia, the results of the evaluation of bearing capacity coefficients due to quasistatic load in numerical modeling are more conservative and in all cases more reliable than the results obtained from other researchers. Finally, given that quasistatic load is not an ideal alternative criterion for earthquake load impact, the effect of the following soil mass on how earthquake waves are transmitted to the substrate is also evaluated.

5.5 Seismic rehabilitation methods for soil of site The problem of soil consolidation using a variety of methods of improvement is nowadays one of the most important applications of geotechnical science. The construction of structures on unsuitable subgrade and problem soils requires that prioritizing the design and execution of structures for refining operations is a priority. In the case of structures under construction or in operation, if the bed conditions are not properly considered in the design, implementation and subsequent occurrence of subsidence and damage caused by ignoring geotechnical conditions, it will be necessary to implement soil consolidation. So, in this section, a brief description of some soil remediation methods is given.

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Figure 5.11 Seismic rehabilitation methods for soil of site method at the glance.

A suitable subgrade from a geotechnical engineering point of view is a subgrade in which the soil has sufficient bearing capacity and shear strength against design loading and consolidation sessions and expansion and shrinkage volumetric changes due to loading in the soil mass within the permissible range. Therefore, the construction of such an appropriate context in general projects, especially projects on vulnerable soils, will consider the priority of soil consolidation projects in seismic rehabilitation projects [1] (Fig. 5.11).

5.5.1 Know the density of the soil Soil compaction is an important topic in soil mechanics and geotechnical engineering, it is obvious that the soil is an important parameter in construction, as it is necessary to evaluate the current conditions of the site for the project to meet the project purpose. In general, soil compaction is the process of increasing soil density, which will be accompanied by the outflow of air between the soil particles and the attainment of target resistance. But consolidation is a process by which the amount of water in the saturated soil is reduced without air being replaced by water. The major difference between these two phenomena is that soil compaction is carried out by interfering with external forces and applying them to the soil, resulting in a decrease in the space between the soil particles and ultimately a decrease in soil volume. Consolidation, on the other hand, is the process of condensing or reducing volume without the intervention of foreign forces. So soil compaction is a process that can be achieved naturally or by mechanical and artificial techniques. In the natural compaction process, the mechanical forces exerted by the machinery are not interfered with and the soil is compressed by natural forces such as animal and

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human traffic, pressure of the top soil layers, evaporation of water between soil particles and other natural effects over time.

5.5.2 The importance of soil compaction in the construction industry Soil characteristics in the land area vary according to climatic and geographical conditions. So obviously with the change of location the soil profile will also be different. The soil of a site may not have all the characteristics required for construction for some reason, but these properties can be altered by methods and processes. In general, the local soil selected for a construction project must be sufficiently resilient, relatively compressible to prevent future meetings, be resistant to volume change, and persist against chemical attacks and permeability. Have a good time. Soil under a structure, under pavement of roads, dams, power plants, tunnels, etc. must be compacted prior to construction (Fig. 5.12).

5.5.3 Definition of site rehabilitation Controlled rehabilitation of in situ soil is to use it in a new geotechnical structure. In seismic rehabilitation of site soil, following characteristics are considered as main criteria. • In situ soil is modified. • Its characteristics reach the acceptable level. • Ground becomes a part of soil structure system.

5.5.4 Seismic/replacement methods of compaction rehabilitation These are widely used in static, dynamic, and earthquake loading modes. In these methods, by using deep vibrators the soil is compacted or reinforced.

Figure 5.12 The importance of soil compaction in the construction industry.

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5.5.5 Compaction stages The process of seismic compaction in the soil vibratory method consists of three stages of permeation, compaction, and soil filling (Fig. 5.13).

5.5.6 Dynamic compaction Dynamic compaction is a method that is used to increase the density of the soil when certain subsurface constraints make other methods inappropriate. The process involves dropping a heavy weight repeatedly on the ground at regularly spaced intervals. Dynamic compaction is the increase in soil density deep below the ground by the impact of a heavy object. The loading weight is approximately 010 tons, which is released from a height of 1530 m and compresses the ground in a 2.5 3 2.5 to 6.5 3 6.5 grid (Fig. 5.14). This type of compaction creation includes the applications and constraints presented in the below information. Applications of dynamic contraction are: • Reduce in foundation settlement • Possibility of made grounds

construction

• Compaction of landfill for construction on • Modification of mining surplus storage sites

Determining the maximum depth of ground improvement (D) The most compacted part is the two-third of upper part of effective depth, where energy level of each impact is weight 3 drop height. In this regard, power intensity factor is a combination of energy level, impact

Figure 5.13 Compaction stages of soil.

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Figure 5.14 Dynamic compaction of soil.

Figure 5.15 Dynamic compaction of soil.

intervals, and number of impacts.

pffiffiffiffiffiffiffiffiffi D 5 α WH

(5.2)

W the weight of the Kent ledge (ton); H drop height of the weight (m); and α the modification factor between 0/3 and 0/7, depended to the soil type (Fig. 5.15).

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5.5.7 Preloading One of the oldest methods in rehabilitating fine-grained lands is preloading. In this method, by applying temporary load to the soil through the embankment to the extent of the minimum load of the structure, soil settles and its strength increases. If the soil settling time is long, it is accelerated by preloading using vertical drainage (Fig. 5.16).

5.5.8 Seismic rehabilitation with grouting Another method that increases the permissible load-bearing capacity of soil and also prevents water leakage in structures such as dams is soil rehabilitation by grouting method. The basis of this method is to fill gaps, voids, and ground pores with grout that prevents excessive settlements and retrofits the soil base below. Other applications of this method include increasing the lateral loading strength of piles, fixing gables, increasing soil-bearing strength and its bearing capacity, permeability change and reducing water absorption percentage, preventing swelling, and settlement. Cement is the most used material in the soil grouting industry. In general, in this grouting method, the soil is first drilled to the desired depth to the usual diameter of 90 mm. The fluid used during drilling is water, air, bentonite, and cement grout (if necessary). In the second step, the jet is applied at a pressure of 400600 times from 1 to 4 nozzles with a diameter of 1.54.0 mm perpendicular to the lower part of the drilling radar. The grout is injected into the nozzle at a speed of 250 m/s and thus combines with the soil around it. During this operation, the rod is rotated upward with a constant speed. As a result, these operations are accomplished by creating columns of soil rehabilitation grout. Improving the grout column

Figure 5.16 Preloading of soil.

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diameter can be done by changing the parameters such as grout velocity and angle, rotation and pulling speed, and number and diameter of the nozzles. Jet grouting method allows to improve various soils from cohesive soils to granular soil such as clay to sandy soils like aggregate. Among effective issues in soil grouting method are purpose of grouting, pressure, type of grouting material, material, and grading existing materials. Therefore, soil grouting methods are divided into the following categories: 1. compaction grouting; 2. permeation grouting; 3. jet grouting; and 4. hydro fracture grouting. 5.5.8.1 General methods of grouting in soil and rock Grouting is a method in which liquid is flowed into pores and cracks (slurry, permeation, chemical, fission, and compaction grouting) with pressure, or by disintegrating poor soil and rocks with slurry (high-pressure grouting) mixes with them and makes the physical and mechanical properties of soil and rock change. The range of application of different grouting methods is determined by the size of the soil grains (Fig. 5.17). 5.5.8.1.1 Permeation grouting in soil

This method is one of the oldest methods of grouting in soil. Seams, fissures, or fractures in the rock and voids in the soil are filled with slurry, without disturbing the structure of the rock or soil with minimal pressure by the slurry. The slurry fluid is grouted with minimum grouting pressure over a period of time in the voids between the soil particles or in the rock slits to prevent new fractures. The main purpose of permeation is to

Figure 5.17 General methods of grouting in soil and rock at the glance.

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reduce the permeability and control of groundwater flow and increase soil strength and to create a more integrated and coherent mass. Grouting of cement into the soil and chemical grouting are of this category. Application of permeation grouting includes: • stone base rehabilitation of dams; • implementing waterproof membrane; • implementing grouting anchors; and • stabilization of sand and stone materials. Grouting materials: • cement, clay and bentonite, sand, concrete additives, fine cement, volcanic ash, lime, and water. 5.5.8.1.2 Chemical grouting

Chemicals are used in grouting if the pore size is too small that ordinary cement cannot permeate the pores. Chemical grouting is performed for two purposes: increasing the resistance to provide higher load-bearing capacity or reducing permeability for sealing. Chemical grouting offers the advantages of being easily performed where access and space are limited, and where no structural connection to the foundation being underpinned is required. A common application of chemical grouting is to provide both excavation support and underpinning of existing structures adjacent to an excavation. It can typically be accomplished without disrupting normal facility operations. Application of chemical grouting includes: • structural protection of wall; • retrofitting foundation; • retrofit and stabilization of tunnel; • excavation below groundwater; • implementing waterproof membrane; and • retrofit and stabilization of piping. Chemical slurry: • sodium silicate, acrylate, acrylamide, polyurethane, and fine-grained silicate cement. 5.5.8.1.3 Compaction grouting in soil

In compaction grouting in soil, by grouting high-viscosity and highpressure slurry in various stages bubbles of slurry are created, causing the soil to be displaced and compacted. This method is applicable to very

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loose and collapsible sandy and fine-grained soils and is applicable to almost all types of soils. This method rarely results in partial displacement at ground level and should be used cautiously in the case of a sensitive site. Some tips for this method are as follows: • The mix design is a special slurry mixture to prevent penetrating into the soil nor to be mixed with it. Instead, it is replaced in the soil being grouted. • Size of voids decreases and the media becomes compacted. • The mortar is hardly grouted into loose soil, and the bubble is made up of grouted mortar and replaced in soil and compacts the surrounding ground without permeating the soil cavities. • In gravel media the compaction is not maximal, but it is more effective in loose fine media. • It is often used in shallow foundations to lift settled slabs. Compaction grouting involves the injection of a low slump, mortar grout to densify loose, granular soils and stabilize subsurface voids or sinkholes (Fig. 5.18). 5.5.8.1.4 Fissure grouting

In this method, building settlement is controlled by grouting slurry into the soil and causing hydraulic fracture in that building. By entering the fissures, controlled slurry cause the soil uplift and compensate previously formed settlements. Grouting is done in several steps at various levels and by doing so, the soil is reinforced and retrofitted (Fig. 5.19). Application of fissile grouting includes: • reduce or reverse the process of the settlement variance; • reduce or reverse the whole process of the settlement; and • prevent buildings from collapsing due to tunneling operations.

Figure 5.18 Compaction grouting in soil methods.

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Figure 5.19 Fissure grouting vertical and horizontal methods.

5.5.8.1.5 High-pressure grouting

When the grouting pressure is greater than the tensile strength of the soil or rock, it causes hydraulic fracturing, failure, and cracking, and the slurry permeates rapidly into the cracked area. This method is used to compact and stiffen the ground or to access other cavities that are not accessible. This method is useful when disrupting soil structure and causing pressure displacement at ground level is not a problem. 5.5.8.1.5.1 Application of high-pressure grouting 1. This method is a good choice for replacement with cement grouting, chemical grouting, slurry walls, geotechnical remediation, or compressed air and freezing systems in tunneling. 2. High-pressure grouting is a good option if groundwater control, excavation in unstable soils with or without groundwater is considered (Fig. 5.20).

5.5.9 Soil mixing This method is the mechanical mixing of in situ soil with additives such as lime cement by hollow augers. The purpose of soil mixing is to achieve modified geotechnical parameters such as compressive strength, shear strength, or permeability. Soil mixing is also used to limit or fix harmful chemicals in the soil (Fig. 5.21).

5.5.10 Underground walls for controlling water level (cutoff) The underground walls are created using shovels, draglines, grub and shoring, and hydro fraise machines. It is used to stabilize the bentonite slurry wall, and after excavation, engineering materials (plastic concrete, cement

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Figure 5.20 Application of high-pressure grouting.

Figure 5.21 Type of soil mixing machine. Source: From https://commons.wikimedia. org/wiki/Main_Page

slurrybentonite, reinforced concrete, and soilbentonite mix) replace slurry. Types of underground walls include a cutoff wall and a diaphragm (structural). The cutoff wall is mainly used to control water in deep excavations, the cutoff wall in dams and flood walls, to control contaminated groundwater, and to create barrages at the disposal site (Fig. 5.22). Diaphragm walls are mainly used for retaining walls, heavy foundations, combined retaining wall and foundation, combined retaining wall and barrage, and for the construction of deep basements top-down method after wall execution (Fig. 5.23).

5.5.11 Nailing (nailing in soil) One of the common methods of soil rehabilitation is wall nailing, and the purpose of such doing is to in situ reinforce of soil mass by installing steel bars (nails) vertically at close intervals on a sloped surface or in an

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Figure 5.22 Underground walls for controlling water level (cutoff).

Figure 5.23 Underground walls for controlling water level (cutoff).

excavation site and filling the cement slurry to prevent corrosion of the bars and better transfer of force. Due to the applicability of this method, it has become very popular in recent years, and in Iran the use of nailing method has been significantly developed and is one of the most applicable methods especially in urban construction [1]. The nailing method creates a stable reinforced section that is capable of holding its back soil. Nails also tend to react in tension, but under certain conditions, their bending and shear performances are also considered. The effect of nailing reinforcement to improve wall stability is achieved by the following two functions: • increasing the vertical force and consequently increasing the shear strength of the slip surface in frictional soils; and • reduction of slip surface thrust in frictional and cohesive soils (Fig. 5.24). A thin, shallow layer including shotcrete and light steel reinforcement as bar fabric is implemented after installing nailing bars on the gable wall

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Figure 5.24 Drilling and mounting operation on retaining wall system for nailing.

Table 5.2 Advantages and disadvantages of nailing method.

Advantages of nailing method

Disadvantages of nailing method

• Stabilizing slopes, gables, and trenches

• In the case of low-volume excavation, the cost of equipping and dismantling the site is high • Requires specialized drilling equipment and specialized workforce • Creates noise pollution • Needs adjacent neighbors’ consent to get started

• Increasing load-bearing capacity and decreasing deformations • Making the least disturbance • Ability to move equipment in low space • Ability to modify design during implementation • Less deformations of the wall (ability of implementation close to structures sensitive to settlement) • Synchronization of excavation and stabilization operations • Less costly than other constructing methods especially fixed protective structures

or well surface to prevent soil surface erosion and create a more suitable surface for construction. A more important purpose of these walls is to increase the efficiency of the reinforced soil system performance, especially in the areas close to the well wall and to better transfer the driving forces to the reinforcing elements. The advantages and disadvantages of the nailing method are summarized in Table 5.2.

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5.5.12 Stone and soil anchoring Soil and rock anchoring is one of the load-transfer systems used to brace stable ground, long tendons, and connect to structures. Applications of this type of stability include side lateral bracing of the wall, hydraulic lift resistance, landslide stabilization, and retrofitting against collapse (Fig. 5.25).

5.5.13 Soil shoring with piling Soil shoring with piling is one of the most important methods of modifying soil rehabilitation and retrofit. In facing with weak soil-load-bearing capacity or high compatibility of the top layers, so that the surface layer cannot be used to distribute the load, there is a need to increase the loadbearing capacity or to transfer power to the lower soil surfaces. In this regard, the excess force is transmitted to the lower surface of the soil by means of a pile or a so-called shoring. In lower level, compaction and friction are higher, so the structure will have the sufficient strength against settlement and existing forces. If the piles are affected by the horizontal force, while still capable of carrying vertical loads, they can also carry horizontal forces by bending. This is often the case in foundations of soilretaining structures that are tasked with resisting lateral soil pressure or tall buildings affected by wind or earthquake forces.

5.5.14 Methods of piling in soil 5.5.14.1 In situ pile The in situ candle is made of concrete and is without any displacements. In situ pile has the most wide application and variety among the used

Figure 5.25 Stone and soil anchoring for upgrading soil capacity.

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Figure 5.26 In situ pile.

technology in this field due to its unlimited diameter and depth of drilling. This method has some advantages that are: • Possibility of increasing the section of the pile at the end and increasing the load-bearing capacity and unlimited diameter. • Completion of studies and identification of soil during drilling and easy supply of required machinery. • Suitable for implementing in urban areas due to low noise and disturbance (Fig. 5.26). 5.5.14.2 Precast piles Precast piles are made with a square section and usually have ordinary bars. Bars are used to retrofit pile against generated bending during transloading, lifting, and applying lateral force to the pile, as well as increasing compressive strength. Precast piles are made in desired length and are operated under humid conditions to achieve the desired strength then they are moved to the site. Shoring operation of precast is done by Schmidt pile hammers to the depth specified in the working designs (Fig. 5.27).

5.5.15 Micropiles One of the most advanced methods in soil rehabilitation is micropile, which, in addition to being added as a load-bearing and resistant element to soil, improves the mechanical (strength and behavioral) properties of the soil following grouting of cement slurry [1] (Fig. 5.28). Engineers have always used two ways to rehabilitate and retrofit soil, including the use of bearing elements in the soil and modification of

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Figure 5.27 Precast piles method.

Figure 5.28 Micropiles method for soil under building foundation.

physical-mechanical properties by adding materials to the soil. Each of these includes specific ways and methods, including the use of micropiles along with cement slurry, which has the benefits of both. Micropiles are piles less than 300 mm in diameter that are often accompanied by light steel reinforcement and grouting of cement slurry. The history of using this method dates back to World War II. With the passage of time due to its efficiency and applicability in damaged buildings as well as its high speed of repair and reinforcement of structures, micropiles became more popular (Fig. 5.29). 5.5.15.1 Applications of micropile method To do a project, first the geotechnical characteristics of the project site have to be studied, then the liquefaction of different depths and potential

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Figure 5.29 Micropiles method for soil under bridge foundation.

Figure 5.30 Micropiles method for soil under foundation.

of liquefaction in the event of an earthquake must be analyzed. Because with occurrence of liquefaction, the shear strength of soil decreases drastically and large settlements occur on the surface of the foundation that causes serious damages and ultimately destruction. In some other projects, the goal is to provide bearing of the columns on the foundations and transfer the load to deeper layers (Fig. 5.30). Micropiles have been suggested as a desirable option in both types of functions. In the first application, regarding the conditions, usually at depths of 10 m near surface liquefaction is dangerous and at depths of over 10 m its effects will be reduced. Therefore, in implementing micropiles, the depth of rehabilitation should be selected in such a way as to be economical while ensuring proper soil behavior in critical conditions such as earthquakes and providing consistent foundation strength against imposed overloads and preventing heterogeneous settlements. Other criteria for

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Figure 5.31 Application of soil rehabilitation methods with micropile.

determining the appropriate depth of micropile implementation are field observations of micropile drive in the soil and recording penetration velocity changes based on the number of drive (input energy). Therefore, as work progresses, the design depth can be adjusted to suit the ground conditions. In the second application, the micropiles implement as well as slurry grouting, in addition to improving soil strength properties, provide for the load bearing of columns on the foundation and leads transfer of load to deeper layers. Therefore, the length of micropile will be calculated according to the required load-bearing capacity. In this regard, the arrangement of piles in the plan and the calculation of their optimum depth are of great importance. Because the order in the arrangement of the micropiles will cause a uniform distribution of the support reaction under the building foundation and the upper structural foundation will also be optimally and homogeneously designed. Factors such as position of columns and foundations, distribution and amount of distributed and concentrated loads, resistance parameters and load-bearing capacity of soil, soil permeability, and depth of micropiles and geometrical and structural properties of foundations are influential in the layout of micropiles (Fig. 5.31). Applications of site seismic rehabilitation are foundation seismic rehabilitation, control groundwater level, quality improvement of ground, stabilization of trenches, and pollution control. Methods of rehabilitation by compacting, making cohesion, reinforcing, physical and chemical changes, excavation and refilling the earth, and biological conversions all try to improve site soil. Table 5.3 provides an overview of soil seismic rehabilitation practices with regard to performance and damage requirements for rapid review (Fig. 5.32).

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Table 5.3 Methods of soil improvement according to purpose. Purpose Method

 Vibrio  Penetration compaction, grouting vibrato  Jet grouting  Stone columns  Compaction  Deep dynamic grouting compaction  Sand and gravel  Gravel drains compaction piles  Deep soil mixing Stabilize structures that have  Compaction  Jet grouting undergone differential settlement grouting  Minipiles  Penetration grouting Increase resistance to cracking,  Compaction  Jet grouting deformation, and/or deferential grouting  Minimiles  Penetration grouting Reduce immediate settlement  Vibrio  Deep soil mixing compaction,  Jet grouting vibrato  Sand and gravel  Deep dynamic compaction piles compaction  Explosive compaction  Compaction grouting Reduce consolidation settlement  Precompression  Stone columns  Jet grouting  Deep soil Increase rate of consolidation  Vertical drains, with or without settlement surcharge fills  Sand and gravel compaction piles Improve stability of slop  Buttress fills  Soil nailing  Compaction  Jet grouting grouting  Gravel drains  Sand and gravel  Deep soil compact mixing  Piles  Penetration grouting Improve seepage barriers  Jet grouting  Deep soil mixing  Penetration  Slurry trenches grouting Increase resistance to liquefaction reduce movements

(Continued)

Site pathology and seismic rehabilitation methods

Table 5.3 (Continued) Purpose

Strengthen and/or seal interfaces between embankments/ abutments/foundations Seal leaking conduits and/or reduce piping along conduits Reduce leakage through joints or cracks Increase erosion resistance

Stabilize dispersive clays

Stabilize expansive soils Stabilize collapsing soils

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Method

 Penetration grouting  Jet grouting  Penetration grouting  Compaction grouting  Penetration grouting  Roller  Concrete compacted  Admixture  Biotechnical stabilization stabilization  Add lime or cement during construction  Protective filters  For existing dams, add lime at upstream face to be conveyed into the dam by flowing water  Lime treatment  Soil replacement  Prewetting—hydro blasting  Vibrio compaction  Deep dynamic compaction  Grouting

Figure 5.32 Application of soil rehabilitation methods with respect to the type of soil.

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5.6 Practical example of site seismic rehabilitation and identify potential damage 5.6.1 Evaluation and define rehabilitation methods trenches of urban development site To accommodate the residents' urban development plan, a residential complex has been built on a steep slope near the residential town. Unfortunately, in this location due to the steep slope of the mountain slopes, it is inevitable that soil and rocky bedding will be placed next to each other. Due to using different stone materials such as hard igneous and tuff, the different stiffness in them has caused extreme geotechnical problems. Due to the topographic effects of the area, the placement of the building blocks and access roads require high volume and high-level excavation and stone-cutting, which takes into account the distance between buildings and access roads, the formation of steep slopes with high altitude is inevitable. Therefore, in this project, concrete wall has been used to provide slope stability. It is important to note the lack of manual soil and bed characteristics for the retaining walls and blocks, which neglecting this issue and not taking into account the weight of the structures and parking lots in the area causes a large displacement in the wall and the structural cracks in the wall and adjacent buildings (Fig. 5.33). In the downstream of the residential complex, reinforced concrete walls are built in the trench area to hold the soil back, are driven off-plate due to soil weathering, and some detaches have occurred in some in-plate parts. The capacity of the wall is evaluated, and finally a rehabilitation

Figure 5.33 Slope with heights more than 10 m with instability potential adjacent to the building.

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method is chosen. The above design provides a static rehabilitation of the wall and prevents possible off-plate drifts. Due to the inaccessibility of the retaining wall structural logbook, and the lack of accurate knowledge of the strength parameters considered for the soil and the structure, according to objective observations, the project seems to be unqualified. In this example, we attempted to examine the structural damage and rehabilitation of concrete trench walls and ways to rehabilitate the bed. 5.6.1.1 Overview of problems Main problems include overdisplacement, structural cracks, total instability of the built wall, deformation, cracks on the buildings, and soil drift. 5.6.1.2 Instability of downstream trenches of buildings Due to the high slope of the topography of the area and considering the geometrical dimensions of the building blocks, steep slopes of high elevation are formed in the vicinity of the buildings, which are necessary for their stabilization. These instabilities will be problematic during construction. 5.6.1.3 Instability of soil trenches under buildings As mentioned, locating adjacent buildings on either side of the slope or at the top of stone and soil slope is inevitable because of the location constraints of the buildings. Under these conditions, the occurrence of high subsidence and general instability under the buildings are very likely, making the operation of buildings difficult (Fig. 5.34). 5.6.1.4 Trench instability access roads Trenches adjacent to the access roads should also be adequately protected to maintain operating conditions. The instability that occurred was mainly due to the low strength properties of the soil and rock layers, weathering of the layers, and change in layering (Fig. 5.35). 5.6.1.5 Problems of foundation-bearing capacity modification Materials with different load-bearing parameters or low strength lead to problems such as subsidence and instability related to load-bearing capacity. Soil materials adjacent to stone layers and changes in stone layer stiffness adjacent to each other under the foundation are the main reasons for problems related to load-bearing capacity of the ground (Fig. 5.36).

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Figure 5.34 Placing the building on a trench and destroying the foundation basement and falling stone.

Figure 5.35 Incidence of instability in slope overlooking the access roads due to weathering and stone layering.

Figure 5.36 Intact soil layers under building foundation.

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5.6.1.6 Stability of soil slope To present an appropriate stabilization plan, the existing information is first collected and the results of the local surveys are summarized. In the next step, by examining the feasible options for protecting the trench walls and comparing the different options technically, economically and runtime, the best option is selected. At this stage, by considering the rules of the bylaws, a blueprint for each of the possible options is prepared. After selecting the appropriate option, complementary numerical analyzes and evaluation of the designs are carried out. The following is an introduction to suitable alternatives for stabilizing soil and rock trenches based on the status of the project. Different methods can be used to stabilize slope and to rehabilitate subsurface soil (Table 5.4). In projects near trenches, the main concern of builders is to provide structure safety near the trench and the trench itself against probable collapse and impermissible displacements. Choosing the right method for stabilization depends on different factors, also choosing the most appropriate and optimized method economically and in terms of runtime needs accurate knowledge about the project and careful study of stabilization methods. Different stabilization methods for trenches are thoroughly explained in the previous chapters, and advantages and disadvantages for each are explained. Here, each of these methods is generally studied without paying attention to details. 5.6.1.7 Examine damage to retain walls that prevent trench displacement The origin of these instabilities and the deformations created in the retaining walls behind the trench and under the parking lot blocks can generally be in terms of materials (shear strength), weathering and alteration of rock properties (tuff stones), and direction change. It is necessary to study the cause of instability in each section carefully and according to geotechnical and geometrical conditions, an appropriate plan should be presented. This example provides an example of seismic rehabilitation of concrete walls that were executed to maintain an existing trench and that are vulnerable. 5.6.1.8 Investigation of the general status of trench design in retaining walls According to field observations, the upper concrete retaining wall has shifted outward from the concrete wall plate about 40 cm above the

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Table 5.4 Improvement and stabilization practices for soil slope. Row Method Row Method

1 2 3 4 5 6 7

Implementation of nailing or anchorage Executing a combined brace or wall Braced walls by bulkhead Bracing by cast-in-place micropile Braced walls by tensile elements Walls braced with diaphragm wall Building retaining wall

8

Executing reinforced soil system

9

Excavation and engineering embankment Cast-in-place micropile Micropile

10 11 12 13 14

Consolidation injection to improve soil performance Building stone columns In-place combination of soil and cementsoil columns

Figure 5.37 Damages in the project.

crown, which causes structural cracks on the wall as well as asymmetric subsidence in adjacent buildings (Fig. 5.37). 5.6.1.9 Introducing seismic rehabilitation methods for existing retain wall (Fig. 5.38) 5.6.1.10 Retrofitting with prepost tensioned cables—anchoring Considering the wall conditions and the preliminary analysis, the use of retaining wall and anchoring is recommended as one of the seismic rehabilitation options. According to preliminary assumptions, the minimum

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Figure 5.38 Introducing seismic rehabilitation methods for existing retain wall.

length of braces is 18 m on average and they are placed 3 m distance from each other vertically and horizontally. The braces used are six intertwined strands and their number is 4 at the height of the wall. An example of this wall is shown below. Due to the existence of the made ground behind the wall and the height of about 15 m of the wall, excavation is not economically justified. 5.6.1.11 Retrofitting with construction of new restrained building Construction of a load-bearing block adjacent to the vulnerable wall is suggested as another seismic rehabilitation option. For this purpose, excavation is carried out at the specified distance in the design and concrete reinforced block of certain dimensions is executed. The soil behind the wall is then removed and the wall and block are joined by a restraint (brace/strap). Finally, the soil is layered and compacted. Because of the upstream building and the double surcharge behind the wall, this project is not possible.

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5.6.1.12 Retrofitting with existing retain wall and added new buttresses To maintain the stability of the above retaining wall, concrete spacers with specified spacing are used. According to the original design, the strut columns run every 3 m from the retaining wall. In the foundation bed, the above wall uses a micropile. Due to downstream traffic and limited space, this project cannot be implemented. 5.6.1.13 Retrofitting by increasing wall section In the downstream area of residential communities, it has been observed that reinforced concrete walls have been constructed to maintain soil 15 m outside the downstream access level that is under pressure by soil, buried 4 m into the ground, and completely enclosed with soil from the two sides. These walls consist of 3-m panels consisting of 2-m stands and the rest of the cross-sectional area of the wall is 25 cm. It is assumed that the grade of concrete consumed is 250 kg/m3 and its compressive strength due to cracks and deformations is between 150 and 200 kg/cm2. In this regard, to increase the bearing capacity of these walls to prevent trench drift, the retain wall thickness is increased. Drift control in the crest of the wall indicates the inability of the wall against overturning. In this regard, we investigate the overturning capacity of the wall. Ka :0:63; ϕ:22; γ:1920

kg ; Mo :136; 080 kg m; MR :106; 875 kg m m3

MR :0:78 , 1:75-Not ok Mo In this case, the wall will overturn. According to the inspection, it is observed that this deformation has occurred in the retaining wall structure and might overturn at any time. Rehabilitation for the wall reinforcement structure due to the lack of stability of the existing wall, a new reinforced concrete wall must be constructed in the area between the two legs with a thickness of 75 cm as a reinforced concrete wall. At the level of the heel access path 1 m in thickness of the wall 1.2 m from the wall. In some cases, the decision to build a micropile is required.

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Ka :0:63; ϕ:22; g:1920

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kg ; Mo :136; 080 kg m; MR :242; 250 kg m m3

MR :1:78 . 1:75-ok Mo Considering the location of the building blocks and the access roads, the necessity of temporary and permanent trench stability was considered. In addition, due to the deformation of the walls and the surcharge of parking and buildings and the creation of structural cracks in the buildings located above, seismic stabilization and rehabilitation of the retaining wall due to proximity to the building blocks is required. 5.6.1.14 Conclusion This section introduces the general specifications of the project, considering the importance of the project and the deformations created in the retaining wall, structural sustainability control has been carried out and a suitable design has been provided according to the project needs to provide seismic stability and rehabilitation. The use of retaining wall cross section and heel implementation are suggested as the options due to the low level of information (Fig. 5.39).

5.6.2 Improvement of the site against the scouring and fluidization phenomena in the structures around the river 5.6.2.1 Introduction The example is for several residential buildings, built in the seasonal riverside. The observation of heterogeneous subsidence in existing structures

Figure 5.39 Retain wall divided component for retrofitting.

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Figure 5.40 Sample of execution of buildings in seasonal rivers.

near the riverfront led to special studies on the underlying soil structure under foundation. In the process of studies, it was found that the water permeability in the lower layer increased over time, which eventually led to an increase in soil saturation. In this case, the initial bearing capacity of the soil under foundation is drastically reduced. This has led to cracks in the walls of buildings near the river and the saturation process is in progress. In this regard, soil rehabilitation studies have been carried out as described below for the project and finally the appropriate rehabilitation method has been presented (Fig. 5.40). 5.6.2.2 Technical specifications of influential elements in the improvement process 5.6.2.2.1 Technical specifications of existing buildings

Buildings in this complex are two-story buildings with concrete structures and strip foundations. Fortunately, structural and architectural plans are available. The length and width of the building are 1000 cm 3 1000 cm. As a result, the following information was extracted from the plans. The height of the floors is 350 cm for the first floor and the height for the second floor is 350cm550cm. The building, according to the accompanying image, consists of eight columns. All columns are square by 45 cm 3 45 cm in dimensions (Fig. 5.41). The dimensions of the side beams are 45 cm 3 45 cm and the midbeam is 45 cm 3 65 cm. The first floor roof is of concrete block joists and the second floor is of concrete slab structure. The foundation of this building is spread type 100 cm 3 100 cm in depth 60 cm with horizontal ties 50 cm 3 50 cm according to the attached image. The middle column

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Figure 5.41 Plan of existing building.

connected together with strip foundation. Live loading in this building is for residential purposes. Also, the area's snow load is semiheavy. 5.6.2.2.2 Technical characteristics of the soil structure

Given that no information is available on soil mechanical properties. Therefore, in the catheterization and testing agenda, borehole drilling was used to determine these parameters. 5.6.2.2.3 Technical characteristics of the site

As shown in the image below, the buildings under study (zone two) are located 3500 cm from the river and some of the buildings were damaged within area (zone one) 3000 cm of the river (Fig. 5.42). 5.6.2.3 Determination of mechanical properties required by tests for site soil Two boreholes were drilled at a depth of 2000 cm to determine the soil profile. The information is presented in Table 5.5. 5.6.2.4 Evaluation of soil-bearing capacity Based on the existing foundations dimensions and the characteristics extracted from the results of drilled boreholes, we have to use the TERZAGI equations. 1 qu 5 C:NC 1 q:Nq 1 γBNγ -qu 5 178:43 Kpa-1:81 kg=cm2 2

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Figure 5.42 Plan of existing site.

Table 5.5 Mechanical properties of subfoundation soil for quantitative capacity assessment. Row Height (cm), t Type of layer φ C γ ðKN=m3 Þ

1 2 3

0300 3001000 10002000

S.M (organic clay) S.W, S.P (medium density) S.W, S.P (high density)

27 30 40

0 0 0

15.7 18.1 19.4

! 2

Nq 5

e

ϕ 3π 4 22

0

tanf

1 5 15:89 π f 2 cos2 @ 1 A 4 2

NC 5 cotϕðNq 2 1Þ 5 29:23

0 1 1 @ KPγ 2 1A 5 11:6 Nγ 5 2 cos2 ϕ

5.6.2.5 According to building weight (Table 5.6)

5.6.2.6 Rehabilitation method According to the results presented in Table 5.6, it is recommended to use micropiles in the following areas to prevent immediate and potential building meetings and to attach the structure to the appropriate soil layer by micropiles. In this project, micropiles with a diameter of 100 mm and l2 m length were used to rehabilitation the soil and increase the capacity of the foundation soil basement. According to the Meyer-Hoff method, the capacity of each micropile is about 25 KN. In this regard, for the improvement of two columns in the middle of the north and south sides of the building, four

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Table 5.6 Consider the need for soil rehabilitation with micropiles for the example above. Row Elevation P ðKpaÞ for column qallow ðKpaÞ Result

1 2

1,3(A,C) 1,3 (B)

3

2

33.75 66.5

59.47 59.47

134.375

59.47

It’s ok Need rehabilitation by build pile Need rehabilitation by build pile

Figure 5.43 Soil seismic rehabilitation methods sample with micropile.

micropiles should be placed under each foundation. Also in the eastern and western part of the building under the middle columns should be done to make sure that there are two micropiles. The micropiles were properly attached to the old foundation by creating a suitable drill [1] (Fig. 5.43).

Reference [1] Federal Highway Administration Design Manual: Deep Mixing for Embankment and Foundation Support, Publication No. FHWA-HRT-13-046, October 2013.

Further Reading American Federal Emergency Management Agency (FEMA) (356). Prestandard and Commentary for the Seismic Rehabilitation of Buildings. Islamic Republic Vice Presidency for Strategic Planning and Supervision Office of Deputy for Strategic Supervision, Department of Technical Affairs, Code. No (360), First revision, Instruction for Seismic Rehabilitation of Existing Buildings.

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Chapter at the glance

CHAPTER SIX

Seismic rehabilitation: infographics Aims By reading this chapter, you are introduced to: • • • • •

learning how to choose a building at a glance using the infographic method; learning about seismic rehabilitation of existing masonry buildings at a glance using the infographic method; learning about seismic rehabilitation of existing steel buildings at a glance using the infographic method; learning about seismic rehabilitation of existing concrete buildings at a glance using the infographic method; and learning about seismic rehabilitation of nonstructural components using the infographic method.

Seismic Rehabilitation Methods for Existing Buildings. DOI: https://doi.org/10.1016/B978-0-12-819959-6.00006-3

© 2020 Elsevier Inc. All rights reserved.

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Index Note: Page numbers followed by “f” and “t” refer to figures and tables, respectively.

A Acceleration, nonstructural components that sensitive to electrical and telecommunication equipment, 583 elevator, 584 liquid reservoirs and water heaters, 582 583 pipes and connections, 583 shelters, sides, and chimneys, 581, 582f shelves, 583 stepped ceiling, 581 stepped floors, 581 thermal and cooling installations, 582 Acceptance criteria, 52, 222 223, 249 260, 447 454, 458 461, 466 467, 469 472, 484 for beams, 449 for CBF brace and EBF brace, 477 for column in linear and dynamic static analysis method, 251 for columns, 449 450 connection in FR moment frame, 452 454 connection between foundation and base plate, 454 for connections, 467 deformation-controlled members, 447 448 force-controlled members, 449 for nonstructural on seismic rehabilitation objective nonstructural components sensitive to acceleration, 581 584 nonstructural components sensitive to deformation, 578 581 for panel zone, 450 451 for primary members, 466 in static and dynamic linear methods, 252 255 for structural components capacity, 146

for linear methods, 146 for nonlinear methods, 146 Accessories, 569 570 Accidental torsion, 165 Accidents, rehabilitation from perspective of, 5 Acoustic emission, 108 109 test, 108 109 testing method, 108 109 Adaptive precast concrete frames, 320 Adjacent buildings, 214 Adjoining components, attachment to, 183 Alkali-aggregate reaction, 81, 81f Alkali-carbonate reaction, 81 Alkali-silica reaction, 81 Anticorrosion substances, 84 85 ASTM standard, 98 Axial stiffness in deep foundation, 350 353

B Backstay effect, 176 Balanced-base foundation, 31 32 Base isolation units, building retrofit by seismic separation using, 506 508 Baseplate, 86 “Basic” rehabilitation, 43 Basic shear force on building, 215 Bauschinger effect, 505 Beam-column concrete moment frames beams control by flexural, 320 column control, 320 321 connections, 321 323 reinforced concrete moment frames, 311 312 beams, 326 column, 326 327 connections, 327 329 Beam-to-column connection strength evaluation, 446

647

648 Beam(s), 13 acceptance criteria, 250 251 foundation, 32 strength, 445 446 BECOME SEISMIC REHABILITATION, 1 2 Bending test, 104, 105f Binary force linear behavior model, 394 Bleeding concrete, 82, 82f Block joints, 15 Boiling smooth sand, 57, 57f Border crack, 236 Boundary elements, 479 Brace frame, 472 479 acceptance criteria for CBF brace and EBF brace, 477 bracing systems, 474 linear analysis method, 474 475 nonlinear analysis and evaluation method for CBF brace, 478 479 Brazilian test, 100 Brick, 88, 88f arched vault roof and floor form, 18 19, 18f compressive strength test, 112, 112f foundation, 35 36, 36f Brick walls, examining methods for analyzing of frames with, 239 260 analysis method, 241 compressive strength of existing masonry materials, 239 evaluation of masonry infill wall, 241 260 expected elastic constant, 240 expected shear modulus, 240 expected shearing strength, 240 tensile strength in bending, 240 Brickwork of interior partitions or partitioning, 578 580 Brinell stiffness, 106 Building frame system, 28, 28f separation in seismic rehabilitation, 183 184, 184f specifications, 40 41 types and constituent elements, 12 39, 13f

Index

foundations, 30 37 materials and evaluating with criteria, 13 nonstructure components, 38 39 seismic lateral and gravity structure main systems, 26 29 structural roof, 14 26 types in seismic rehabilitation grouping, 39 weight, 634

C Carbon dioxide, 80 Carbonation, 80, 80f Carbonization process, 80 Catastrophes, 2 3 Categorizing buildings, 45 Categorizing structural systems, 27 Cathode protection, 86 CBF brace, linear analysis method for, 474 475 Ceiling diaphragm, 175 design criteria, 175 177 Ceiling evaluation in masonry building, 229 openings in ceiling, 229 ratio of ceiling for span to width, 229 support of length of ceiling beams, 229 thrust force control on floor arch, 229 Cement, 609 610 Centralized rehabilitation, 187, 187f Charpy impact test, 105, 106f Checklist architectural components, 568 570 accessories and permanent interior and exterior ornaments, 569 570 doors and exit paths, 568 569 embedded partition wall, 568 lightings, 568 stepped ceilings and soffit/intrados coverings, 568 windows, 569 Checklist for nonstructural component hazards in earthquake first part of checklist, 563, 564t second part of checklist, 563 572 of components of facilities, 564 565

Index

electrical devices, 565 emergency power generating equipment, 564 565 fire communications and extinguish system, 565 liquid gas storage, 565 567 Checklist furniture and interior content of building communication systems and emergency communication systems, 570 document storage room, 571 furniture and interior decoration, 572 hazardous materials, 572 kitchen and laundry appliance, 572 office supplies and computer equipment, 570 571 Chemical grouting, 611 Chimneys, 581 Chloride attacks, 78, 78f Chord components, 174 in diaphragm, 173 178, 174f Circular slippage, 58 Civil engineering sciences, 1 2 COBIAX roof, 23 24, 24f Codification of modern regulations, 11 Coefficient of P Δ effects, 160 161, 171 value, 171, 171t Coefficient of variation (C.O.V), 311 Collapse occupancy, structural performance level of, 47 49, 48f Collectors in diaphragm, 173 178, 174f Columns, acceptance criteria, 249 250 Combined concrete systems, 303 304 Combined foundation, 32, 33f Combined system, 29, 29f Compaction grouting in soil, 611 612, 612f stages, 607, 607f Components strength, 445 447, 463 466 beam-to-column connection strength evaluation, 446 beams strength, 445 446 column base plate strength evaluation, 447 determination, 315

649 evaluation of, 446 panel zone strength evaluation, 446 Composite frame, 232 233 roof, 24 25 Compound ceilings, 21 roof, 20, 20f, 21f Comprehensive assessment of vulnerabilities digging required in quantitative evaluation and modeling of building structures, 309 310 methods, 573 577 classification of nonstructural components, 573 574, 574f investigating requirements of nonstructural components rehabilitation, 573 nonstructural components analytical procedure, 573 quantitative assessment of nonstructural components vulnerability, 575 577 seismic load for evaluation of nonstructural components, 574 575 number of tests required based on seismic rehabilitation objectives, 310 311 quantitative evaluation of concrete buildings components, 311 354 for soil-bearing capacity, 604 specification of materials, 308 309 expected strength of concrete materials, 309 lower-bound strength of concrete materials, 309 Comprehensive level of information, 117 118 Compressive strength, 112 113 of bricks in walls, 281 of existing masonry materials, 239 Computer equipment, 570 571 Computer modeling methods of site component capacity, 604

650 Computer modeling of site component capacity, 604 Concoctions, 441 Concrete, 427 braced frames, 312 infill, 359 jackets, 357 masses, 123 molding type, 20 21 seismic rehabilitation of concrete ceiling, 360 separation of concrete particles, 81 shear walls, 331 340 simple frame, 301, 302f with shear wall, 303 slabs, 15 roof, 21 23, 22f strength, 97 104, 97f structure column, 303 Concrete frame with infill, 331 340 modeling of, 332 static and dynamic linear method, 333 336 static and dynamic nonlinear analysis method, 336 340 types of reinforced concrete shear wall, 332 333 with pin connection and precast sections, 301 302 structures, 301 302 Concrete materials, 84, 85f buildings with, 39 pathology in, 76 82 alkali-aggregate reaction, 81 bleeding, 82 carbonation, 80 chloride attacks, 78 construction errors, 76 de-icing salts, 79 designing errors, 76 fire, 77 78 frost action, 79 ingress of salts, 76 separation of concrete particles, 81 sulfate attacks, 78

Index

Concrete moment frame, 301, 302f, 311 331 acceptance criteria beam-column concrete moment frames, 320 323 precast moment frame, 324 slab-column moment frame, 324 evaluating capacity of components, 316 320 connections evaluation in linear limitation, 317 318 flexural strength of slab, 318 319 slab-column connections strength, 319 320 strength evaluation for beams, 316 317 strength evaluation in columns in linear analysis method, 317 linear analysis and evaluation method, 313 315 calculation DCR of components, 313 connections, 315 determining components’ strength, 315 determining stiffness of components, 313 314 nonlinear analysis and evaluation method acceptance criteria, 326 331 determination of stiffness of components, 324 determination of strength of components, 325 326 including shear wall, 304 tall 22-story concrete moment frame building, 396 435 three-story concrete moment frame building, 368 396 seismic rehabilitation steps for project, 369 396 types, 311 312 Concrete structure frame buildings comprehensive assessment of vulnerabilities, 308 354 rapid vulnerability assessment, 306 308 seismic rehabilitation techniques, 354 367 types, 301 304

651

Index

combined or dual concrete systems, 303 304 concrete frame structures, 301 302 frame less structures with shear wall and rigid diaphragm, 302 303 understanding potential structural damage, 304 306 corrosion in concrete and rebars, 305f system weakness in concrete buildings, 306 Concurrency effect of earthquake component in linear dynamic analysis, 168 169 Condition acceptance criteria methods, 452 454 Connections evaluation in linear limitation, 317 318 seismic rehabilitation of, 361 362 Consolidation process, 605 606 Construction, 4 5 errors, 76, 77f soil compaction in construction industry, 606 Continuity plate, 452, 494 495 Controlling overturning effects, 146 150, 147f, 148f overturning criteria in nonlinear methods, 149 150 Coring concrete, 98f zone position, 121f Corner crushing mode, 236 237 Corner failure strength, 247 248 Corrosion, 83 86 corrosion of steel inside concrete and masonry material, 84 corrosion steel buried in soil, 86 of inner-structure steel in building, 84 metal corrosion in facilities of building, 84 85 of steel outside building structure, 83 84 Coupling beams, 336, 339f C.O.V. See Coefficient of variation (C.O. V) CQC method, 53 Crisis management buildings, 558

Crisis-stricken people through rehabilitation and precrisis management, 6 Crystallization, 78

D Damage to beams (D.B), 490 Damage to column flanges (D.C), 490 491 Damage to panel zone (D.P), 490, 493 connection failures, 493 Damage to shear coupling plate of beam web, 491 492 Damage to shear web plate (D. S), 490 Damage to Welding (D. W), 490 Dampers, seismic rehabilitation method using, 505 506 D.B. See Damage to beams (D.B) DBE. See Design base earthquake (DBE) D.C. See Damage to column flanges (D.C) DCR. See Demand-capacity-ratio (DCR) DE. See Design base earthquake (DBE) De-icing salts, 79, 80f Dead load, 282 Decision-making process, 2 Decorative dome, 543 Decorative stones, 580 Deep foundation axial stiffness in, 350 353 evaluation stiffness parameters on, 346 347 rotational stiffness in, 353 Deep foundation, 34 Defects evaluation and identification of defects in traditional masonry buildings, 210 211 identification and analysis in building, 209 212 Deformation controlled by, 140 141, 140f nonstructural components sensitive to brickwork of interior partitions or partitioning, 578 580 decorative stones, wood, and interior mirrors, 580 equipment conveyors, 581

652 Deformation (Continued) staircase, 580 walls, exterior walls, façade, 580 Deformation-controlled members, 170, 447 448 Demand for buildings evaluation, 282 285 controlling foundation of building, 282 283 modeling for analysis, 282 vulnerable wall detection, 284 285 Demand modifier factor (m) on nonlinear behavior, 144 Demand-capacity-ratio (DCR), 252, 313 Demolishing volume of executive options, 289 Density of soil, 605 606 Depolarizing agents, 83 Design base earthquake (DBE), 50 Design spectrum, 51 52 designing spectrum preparation, 50 51 of specific site design, 51 52 standard design spectrum, 51 Designing errors, 76 in steel structure, 87, 87f “Desirable” rehabilitation, 43 Destruction, 90 93, 91t Destructive methods, 94, 96t Destructive tests on masonry materials, 110 113 Deterioration in materials, 41 Development length, 315 Diagonal compression failure mode, 237 Diagonal compressive force, 100 Diagonal/tensile diagonal cracking mode, 237 Diaphragm, 14 18, 16f, 18f analysis, 175 chords and collectors in, 173 178, 177t, 178t ceiling diaphragm design criteria, 175 177 chord components, 174 distributer element, 174 175 ties, 177 178 digging roof in, 93 rigidity, 216, 282 Differential settlement, 56, 56f

Index

Digging, 71, 90 93, 91t beams, 92, 93f building components, 91 of ceilings, 275 columns and vertical tie, 92, 93f condition of members and components evaluation, 277 278 connections, 92 and experiments, 273 281 foundation digging, 275 masonry material sections, 275 276 required tests to determine site specifications, 276 vertical and horizontal ties and connections, 275 foundation, 92, 92f masonry material component, 93 maximum and minimum of strength of material, 279 281 plans and agenda, 118 required in concrete building, 309 310, 310f roof in diaphragm, 93 stage, 120 122 and tests, 375 380 building configuration based on digging and tests, 377 380 examining number and adequacy of project building experiments, 376 minimum and maximum material strength regarding test results, 380 rapid qualification of vulnerability, 377 soil and foundation, 380 specification by service and test consultant, 380 underground water and fluidity background, 279 Displacement-dependent devices, 506 Distributed rehabilitation, 187, 188f Distributer element, 174 175, 175f Document storage room, 571 Doors and exit paths, 568 569 Downstream trenches instability of buildings, 598, 598f, 625 D.P. See Damage to panel zone (D.P) Draught water forces, 59, 59f

Index

Drilled piers. See Drilled shaft foundation Drilled shaft foundation, 349 354, 352f. See also Shallow foundation accept criteria, 354 capacity parameters, 353 354 stiffness parameters, 350 353 D.S. See Damage to shear web plate (D. S) Dual concrete systems concrete moment frame including shear wall, 304 concrete simple frames with shear wall, 303 Ductility, 139 141 structural component’s action control, 140 141 D.W. See Damage to Welding (D. W) Dynamic compaction, 607 608, 608f Dynamic linear method, 333 336 acceptance criteria for components, 335 336, 337t determining stiffness of components, 333 334 determining strength of components, 334 nominal shear strength of shear walls, 334 335 Dynamic nonlinear analysis method, 336 340 Dysfunction, 4 5

E E-beam, 475 Earth-accelerated stimulus, 53 Earthquake, 1 2, 6, 65 66, 556, 560 earthquake-related parameters, 74 75 forces, 10 11, 16 18 hazard analysis and designing spectrum preparation, 50 51 design spectrum, 51 52 level in seismic rehabilitation, 50 52 loads, 146 nonstructural component hazards in, 563 572 perspective of designing buildings against, 7

653 simultaneous impact in orthogonal direction, 151 site on, 594 597 soil behavior on seismic waves, 596f site specifications in earthquake risk, 374 375 vertical component effect, 151 vertical effects, 185 waves, 593 594 Eccentric braced frames, 475 linear analysis method for, 475 476 steel eccentric braced frames, 475 stiffness of components for EBF brace frame, 476 strength of components, 476 Economic project-based considerations, 68 69 Economic value for seismic rehabilitation for existing buildings, 187 189, 189f Effective fundamental period, 157 Effective parameters and operations, 135 152 acceptance criteria for structural components capacity, 146 controlling overturning effects, 146 150 demand modifier factor (m), 144 ductility, 139 141 effects of P delta, 151 152 effect of vertical component of earthquake, 151 knowledge factor, 143 load distribution, 144 145 simultaneous impact of earthquake in orthogonal direction, 151 soil and structure interaction, 150 stiffness, 137 139 strength, 142 143 18-story steel special moment frame building 1 concrete shear wall, 525 551 additional information to evaluate qualitative vulnerability, 533 536 building modeling for simulation, 531 compiling and extracting comprehensive structural information, 531 533 evaluating situation in building plan, 536

654 18-story steel special moment frame building 1 concrete shear wall (Continued) interpretation, 542 547 interpreting seismic rehabilitation methods, 547 551 irregularities in building height, 536 542 three-dimensional simulation in computer software, 533 Elastic fundamental period, 155 Elastic modulus, 137 Electrical devices, 565 equipment, 583 machinery, 110 system, 557 558 Electrochemical process, 78, 83 Electromagnetic test, 110 Elevators, 566 567, 584 Embedded partition wall, 568 Emergency power generating equipment, 564 565 Energy amount, 105 106 Environment preservation, 5 6 Equipment conveyors, 581 Equivalent static analysis, 52 Escalators, 566 567 Essential rehabilitation to confront decaying effect of time, 5 Execution control of masonry units, 226 228 controlling load-bearing beams of ceiling, 228 controlling openings distance from bottom of wall, 228 free wall length control, 227 of height to wall thickness ratio, 227 pipes and chimneys inside load-bearing wall, 228 of toothing, 228 of vertical bound of brickwork, 227 wall density control, 227 228 wall height control, 227 Existing building components, 94 125 experiments of material, 95 114

Index

material strength experiments, 96 114 mechanical specification of materials, 96 number of experiments, 114 118 methods of experimenting, 94 95 destructive methods, 94 nondestructive methods, 95 Existing buildings, seismic rehabilitation of methodology for developing seismic rehabilitation strategies, 185 191 economic value for seismic rehabilitation, 187 189 intervention in architecture, 189 190 performance pattern in seismic rehabilitation targets, 191 seismic rehabilitation philosophy in compilation of metallurgy, 185 187 seismic rehabilitation studies with applied approach, 65 75 product and documentation of seismic rehabilitation studies, 66 73 seismic rehabilitation regulation and scope, 73 75 strength of materials in existing buildings, 75 125 vulnerability of existing buildings, 125 185 Existing buildings, technical specifications of, 632 633, 633f Existing retain wall, seismic rehabilitation methods for, 628, 629f Expected compression strength of CBF brace, 474 475 Expected elastic constant, 240 Expected lateral strength (QCE), 220 Expected masonry shear strength capacity (Vme), 219 Expected material specifications, 442 Expected shear modulus, 240 Expected shearing strength, 240 Expected strength of concrete materials, 309 for materials, 281 Expected tensile strength for brace for CBF brace, 475

655

Index

Extensive (MAT) foundation, 32 33, 33f Exterior walls, 580

F Façade, 580 damage, 38f Fault distance from of site, 55 risk, 55 FEMA 310, 306 308 FEMA 356, 431 Fiber reinforced polymer (FRP) composites, 504 seismic rehabilitation method using, 504 505 fibers, 355, 362 363 Filling digging place with concrete masses, 123 Fire, 77 78 communications and extinguish system, 565 in steel construction, 87, 87f Fissure grouting, 612, 613f Flat slippage in stone, 58 Flexibility, 313 314 Flexible diaphragm, 17 Flexural members in frame, 485 Flexural strength of moment frame, 316 317 of slab, 318 319 Floor ceiling, 275 Force force-controlled behavior, 183 force-controlled function, 177 179 force-controlled members, 449 force-delivery reduction factor, 144, 145t force deformation curve, 138 139 on wall, 182 post, 181 182 Foundation(s), 30 37, 31f analysis, 340 354 access and height restrictions, 344 general objectives of seismic rehabilitation, 340 343 restrictions due to existing mechanical installations, 344

digging, 92, 275, 278 evaluation, 431 foundation-bearing capacity modification, 625 626, 626f modeling, 382 regarding consumable materials, 34 37 brick foundation, 35 36 mortar foundation, 35 reinforced concrete foundation, 37 steel foundation, 36 stone foundation, 35 rehabilitation, 394 395 soil and, 380 types, 344 354 in buildings, 30 34 drilled shaft foundation, 349 354 foundation condition, 344 349 regarding consumable materials, 34 37 shallow foundation, 30 34 Frame collapse mode, 242 243 Frame less structures concrete structure column and rigid diaphragm structure, 303 shear wall, 302 Framed structures, 437 438 Free wall length control, 227 Freezing, deterioration factor, 79 Friction separators, 508 FRMF. See Fully restrained moment frame (FRMF) Frost action, 79, 79f Fully restrained moment frame (FRMF), 438, 444 461 fully special restrained steel moment frame, 511 512 linear analysis method, 444 454 nonlinear evaluation method, 454 461 Functional sensitivity, 573 574 Fundamental period of structural oscillation, 155 158, 156t Furniture and interior decoration, 572

G Gamma, 109 Geotechnical hazards, 593 594 Geotechnical tests, 204 207

656 Geotechnical tests (Continued) results, 215 Global engineering society, 65 66 Gravity bearing members, 14 and lateral load structure, 272 273 evaluating regularity in plan in terms of quality, 272 evaluation of regularity in elevation in terms of quality, 272 273 load, 520 gravity load-bearing system, 372 Grouting, seismic rehabilitation with, 609 613 methods of grouting in soil and rock, 610 613

H Hazardous materials, 572 Heating and air-conditioning system, 567 Heating systems face corrosion, 84 85 Heterogeneous settlement, 56 Hidden intervention, 189 High subsidence, 55 56 High-pressure grouting, 613, 614f Homogeneous materials, 104 Honeycomb phenomenon, 76 Horizontal bracing, 474 Hybrid system, 29, 29f Immediate occupancy, structural performance level of, 46, 47f

I In situ pile, 617 618, 618f In-depth manner, 1 2 In-place shear wall, 332 In-plate behavior of walls and bases of masonry materials, 218 223 Inconsistency in vertical direction, 214 Indicators and criteria for seismic rehabilitation, 39 54 general status of building to evaluate vulnerability, 40 42 building and future uses, 41 42 building specifications, 40 41 defects in designing and construction problems, 41

Index

deterioration in materials, 41 nonstructural components, 42 methods of structure analysis, 52 54 target performance level for seismic rehabilitation, 42 52, 44f categorizing buildings, 45 earthquake hazard level in seismic rehabilitation, 50 52 performance levels, 45 49 Infill, 243 244 control in linear behavior, 251 255 control within range of nonlinear behavior, 251 252 frames, 232 233 analyzing behavior of, 180 181, 180f, 181f with opening area, 244 245 walls, 179, 179f, 180f Infographics, 637 Ingress of salts, 76, 76f Inner-structure steel in building, 84, 85f Integrated slabs, 32 Integration of building parts, 182 184 attachment to adjoining components, 183 building separation in seismic rehabilitation, 183 184 parts of building, 182 183, 183f and consistency in accessible areas, 515 Integrity of masonry building, 212 213 Interfacial strength in linear and nonlinear behavior range of materials, 248 Interior mirrors, 580 International Society of Rock Mechanics, 101 102 Intervention in architecture, 189 190 hidden intervention, 189 obvious intervention, 189 190 Iron particles, 109 Irregularities in geometry, 213 in height, 213 in mass, 214 in plan, 213

Index

J Joist-block roof, 19, 19f, 20f

K Kanto¯ , Japan, 10, 10f Kermanshah earthquake, 65 66, 66f, 596f, 597 Kitchen appliance, 572 Knowledge factor, 143, 143f, 143t, 270 271

L Land type and underground water surface, 61 Landslide, 60 61, 61f Lateral bearing members, 14 Lateral force distribution, 15, 163f resisting systems, 14, 14f Lateral load-bearing system, 372 Lateral spread and sequential fracture, 59 60, 60f Lateral-torsional buckling of beam, 485 Laundry appliance, 572 Libraries, 164 Life safety (LS), 326 327 structural performance level of, 47, 47f Life span, 5 Lightings, 568 Linear analysis. See also Nonlinear analysis load combinations, 144 methods, 152 169, 317, 444 454, 463 467 acceptance criteria, 447 454, 466 467 for CBF brace, 474 475 components strength, 445 447, 463 466 for eccentric braced frames, 475 476 linear dynamic analysis, 166 169 linear static analysis, 152 166 stiffness of components, 444 445, 463 for moment frame components, 313 315 Linear dynamic analysis, 53, 166 169. See also Nonlinear dynamic analysis

657 application of, 169 effect of concurrency of earthquake component, 168 169 types of, 167 168 Linear methods, 52 53. See also Nonlinear methods acceptance criteria for, 146 linear (equivalent) static analysis, 52 linear dynamic analysis, 53 spectrum analysis method, 53 stiffness in, 138, 138f time history analysis method, 53 Linear static analysis, 52 53, 152 166. See also Nonlinear static analysis assumptions, 152 154 fundamental period of structural oscillation, 155 158 major and unessential components, 154 ratio of application for linear static analysis method, 154 155 seismic force in vertical distribution method, 161 163 seismic lateral load (V) for linear static analysis, 158 161 torsion, 164 166 Lintel beams, 198 Liquefaction history, 55 56 Liquescence phenomenon, 57 Liquid gas storage in emergency power system, heating, or culinary, 565 567 elevators and escalators, 566 567 heating and air-conditioning system, 567 minor mechanical machines, 567 piping system in building, 566 Liquid reservoirs, 582 583 Lisbon earthquake, 9, 9f Live load, 282 Load bearing system, 38 Load bearing wall system, 27 28, 28f Load calculation on building, 207 208 Load combinations for linear analysis, 144 for nonlinear static analysis, 144 145 Load distribution, 27, 144 145 load combinations for linear analysis, 144

658 Load distribution (Continued) for nonlinear static analysis, 144 145 Load path, control of, 212 Load-bearing capacity, 620 621 of foundations, 345 structure, 88 Load-bearing walls, 204 207 connections of building components, 230 connection between load-bearing walls and ceiling, 230 connection between nonstructural wall, 230 connection between walls and ceiling perpendicular to wall plate, 230 connections between load-bearing crossed walls, 230 defects in, 210, 211f evaluating ties components in masonry building, 231 232 evaluating existence of horizontal foundation ties, 231 evaluation of connection of ties, 231 evaluation of ties system through detachment, 231 evaluation of ties through passing pipe, 232 evaluation of wall connection and ties, 232 quality evaluation of concrete ties materials, 231 ties dimension, 232 specifications evaluation, 224 232 of ceilings in masonry building, 229 execution control of masonry units, 226 228 Load-transfer systems, 617 Low-bound specifications of materials, 442 Lower-bound strength of concrete materials, 309 determination of, 281 Lower-bounded compression strength (PCL), 222 Lower-bounded lateral strength (QCL), 220 222 LS. See Life safety (LS)

Index

M Magnetic particle test, 109 Masonry infill, 359 Masonry infill wall, 232 260 bylaws, 236 condition of wall for infill performance, 234 235 distribution of stress in fill frame, 235 236 evaluation, 241 260 frame collapse mode, 242 243 stiffness, 243 246 strength, 246 260 infill frame creating soft story, 235 interaction between frames and infill frames, 235 mechanism of action of infill frames against earthquake force, 236 238 problems of neglecting infill effective of frames stiffness, 233 234 Masonry materials, 84, 85f buildings with, 39 destructive tests on, 110 113, 110f quality control of masonry materials units, 212 Masonry structure buildings comprehensive assessment of vulnerabilities, 203 232 adjacent buildings, 214 analysis of foundations and existing retain wall, 223 224 evaluation of load-bearing walls specifications, 224 232 evaluation of structural components, 204 207, 205t examining methods for analyzing of frames with brick walls, 239 260 foundation, 214 preparing as-built plans, 203 204 quantitative numerical vulnerability evaluation, 214 223 quantitative vulnerability evaluation and analysis, 207 214 methods, 261 267 potential structural damage, 196 202 damages related to integrity of components, 200, 200f

659

Index

damages related to material quality, 198 199 damages related to roof structures, 200 201, 201f damages related to structural walls, 197 198 weakness in foundation as common element of structure and soil, 201 202, 201f weakness in noninstrumental walls and infill, 202 rapid vulnerability assessment, 202 203 real case study examples, 268 298 seismic rehabilitation of components in ceiling level, 265 266 in components in story level, 263 265 of existing buildings, 261 262 in foundation level, 267 types, 193 195 scope of implementing content, 194 195 Material quality, damages related to, 198 199, 199f Material strength in existing buildings, 75 125 quantity evaluation with experiments and digging results, 89 125 visual assessment of quality of materials, 75 89 tests, 204 Maximum earthquake (ME), 51 Maximum probable earthquake (MPE), 50 MDOF system. See Multi-degree freedom system (MDOF system) ME. See Maximum earthquake (ME) Mechanical specification of layers of soil, 280 281 of materials, 96 Mental disorders and stress in crisis-stricken people through rehabilitation, 6 Messina and Reggio earthquake, 9, 9f Metal corrosion in facilities of building, 84 85, 86f Metal joists, 19

Metallurgy of seismic rehabilitation, 185 187, 185f centralized rehabilitation, 187 damage to choose the type of seismic rehabilitation, 186 distributed rehabilitation, 187 prescriptive rehabilitation, 186 Meyer-Hoff method, 634 635 Micropiles, 618 623, 619f, 620f applications of micropile method, 619 623, 621f, 622t Minimum level of information, 114 Minor mechanical machines, 567 Modeling structural load-bearing walls, 208 209 break walls in flexible diaphragm buildings, 209f difference between rigid and flexible diaphragms, 209f Modern masonry buildings, 195 with ties, 196f, 208 evaluation and identification of defects in, 211 212 without ties, 196f Mold-bearing capacity, 20 Moment-centered effect, 137 138 Mortar, quality control of, 212 Mortar foundation, 35 Mortar Shear capacity test, 279 Mortar shear strength capacity, 111f MPE. See Maximum probable earthquake (MPE) Multi-degree freedom system (MDOF system), 171

N Nailing in soil, 614 616, 616f, 616t NDT. See Nondestructive testing (NDT) Nondestructive methods, 95, 95t, 96t methods, 107 Nondestructive testing (NDT), 107, 108t Nonlinear analysis, 169f. See also Linear analysis and evaluation method for CBF brace, 478 479 acceptance criteria, 479

660 Nonlinear analysis (Continued) stiffness of components for CBF brace, 478 stiffness of components for EBF brace, 479 strength of components for CBF brace, 479 strength of components for EBF brace, 479 for final seismic rehabilitation method, 392 393 for moment frame components, 324 331 nonlinear dynamic analysis, 172 173 nonlinear static analysis, 169 171 Nonlinear behavior, 144 Nonlinear dynamic analysis, 54, 172 173. See also Linear dynamic analysis Nonlinear dynamic method, 326, 336 340 component acceptance criteria, 340, 343t determining components strength, 336 339, 341t Nonlinear evaluation method, 454 461, 467 472 acceptance criteria, 458 461, 469 472 nonlinear dynamic method, 458 nonlinear static analysis method, 454 458 stiffness of components, 454 457, 467 468 strength evaluation tips, 458 strength of components, 457 458, 469 Nonlinear methods, 54. See also Linear methods acceptance criteria for, 146 nonlinear dynamic analysis, 54 nonlinear static analysis, 54 overturning criteria in, 149 150 stiffness in, 138 139, 139f Nonlinear static analysis, 54, 138 139, 144 145, 169 171, 421 422. See also Linear static analysis load combinations for, 144 145 Nonlinear static method, 325 326 Nonlinear structure response evaluation, 385

Index

Nonlinear vulnerability assessment, 383 Nonprismatic section beam for cantilever, 411 Nonreinforced masonry infill frames, 260 Nonstructural components, 38 39, 38f, 42, 555 557 acceptance criteria for nonstructural on seismic rehabilitation objective, 578 584 comprehensive assessment of vulnerabilities methods, 573 577 damage to, 557 form for sensitivity determination of vulnerability, 563t hazards in earthquake, 563 572 nonstructural component behavior algorithm in building, 589 591, 590t potential damage, 557 560 assessing nonstructural components careful placement/layout, 559 560 lack of proper bracing of important hospital equipment, 558f lack of proper restraint, 559f long, unbraced cantilever roof at main entrance, 558f rapid vulnerability assessment methods, 560 572 rehabilitation, 573 seismic rehabilitation and evaluation-bearing capacity, 586 589 and reducing danger, 584 585 separation and fall of, 557f structural stability and complete demolition, 556f Nonstructural components Assessment, 559 560 detach facade from wall, 560f proper layout and proper bracing of mechanical installations, 559f Nonstructural connection components, 71 Normal bending interaction, 255 257 Northridge earthquake, 11 Numerical vulnerability analysis, 208 209 modeling structural load-bearing walls, 208 209

Index

O Obvious intervention, 189 190, 190f Office supplies, 570 571 On-site evaluation of concrete strength, 97 One-story unreinforced historical masonry building with nonrigid diaphragm, 290 298 adobe buildings, 290 292 configuring and recognizing existing building specifications, 293 295 mechanical properties of materials, 295 296 progressive damage mechanism in adobe buildings, 293 quantitative assessment of adobe loadbearing wall capacity, 296 297 restoration and rehabilitation in adobe buildings, 293 seismic rehabilitation plan, 298 site specifications, 295 weight of building and effective period, 295 Ophthalmic exam, 109 Orthogonal direction, earthquake simultaneous impact in, 151 Out-of-plane strength, 182f force on wall, 182 force on wall post, 181 182 Overturning effect, 146 148

P Pad foundation, 31, 32f, 33f Paddle foundations, seismic rehabilitation of, 367, 368f Panel zone effects, 452 453 strength evaluation, 446 Parapet wall, 183 Partially restrained moment frame (PRMF), 444, 462 472 linear analysis method, 463 467 nonlinear evaluation method, 467 472 steel moment frame, 512 P Δ effects, 151 152, 153f coefficient of, 160 161, 171 Peak ground acceleration (PGA), 268, 374 Penetrant testing method, 109 110

661 Performance level, 5, 45 49, 144 regulations, 12 structural performance level of collapse occupancy, 47 49 of immediate occupancy, 46 of life safety, 47 Performance pattern in seismic rehabilitation targets, 190f, 191 Permanent interior and exterior ornaments, 569 570 Permanent molding, 20 Permeation grouting in soil, 610 611 PGA. See Peak ground acceleration (PGA) Phosphates, 84 85 Pile foundation, 349, 352f Piling methods in soil, 617 618 precast piles, 618 in situ pile, 617 618 soil shoring with, 617 Pipes and connections, 583 Piping system in building, 566 Plans availability of, 563 geometry, 17, 17f unavailability of, 563 Plastic joints of elements, 419 Pliability, 313 314 Podiums, 176, 176f Polyethylene, 23 24 Polypropylene, 23 24 Postearthquake social damages and crimes, 6 Postinstalled connection systems, 315 Power intensity factor, 607 609 Precast concrete frames, 312 concrete moment frames with pin connection, 320 moment frame, 324, 331 piles, 618, 619f shear wall, 332 333 Precrisis management, crisis-stricken people through rehabilitation and, 6 Prefabricated concrete frames, 319 320 Preliminary information collection in visiting building, 68, 68f

662 Preloading, 609 of soil, 609f Prescriptive regulations, 12 Prescriptive rehabilitation, 186, 186f Prestress technology, 25 26 Prestressed joist, 19 Prestressed roof slab and floor form, 25 26, 26f Pretensioned moment frames, 311 312 Pretensioned reinforced concrete frame, 318 Pretensioning method, 357, 358f PRMF. See Partially restrained moment frame (PRMF) Product and documentation of seismic rehabilitation studies, 66 73 collecting preliminary information in visiting building, 68 experiments and digging, 71 preparation of qualitative evaluation, 68 71 report providing on three-method for seismic rehabilitation of existing building, 72 report of quantities evaluation, 71 72 Progressive/further liquefaction of soil, 56, 57f Pulse penetration rate, 104

Q Qualitative evaluation preparation, 68 71, 69f, 70f of regularity in height, 373 375 in plan, 372 Qualitative vulnerability assessment, 370 372 adjacent buildings, 371 geometric specifications of building, 370 gravity and lateral load-bearing system, 372 groundwater level and history of liquefaction, 371 height to building dimensions’ ratio, 371 identifying seismic rehabilitation objective, 371 inconsistency of building, 372

Index

protrusion and intrusion in plan, 372 specifying knowledge factor, 371 status of opening surfaces and proximpity to floor diaphragm, 372 symmetry in building plan, 371 type of ceiling and structures in existing building, 370 Quality control of masonry materials units, 212 of mortar, 212 Quality/qualitative assessment, 69 70, 562 563 availability of plans, 563 unavailability of plans, 563 Quantitative assessment calculating deformations, 576 577 αp and Rp for architected nonstructural components, 577t αp and Rp for furniture and interior equipment nonstructural components, 578t αp and Rp for mechanical equipment nonstructural components, 579t αp and Rp for electrical and communications nonstructural components, 579t necessary parameters for calculating deformation, 576t for higher than life safety performance level, 576t for life safety performance level, 575t of nonstructural components vulnerability, 575 577 Quantity/quantitative evaluation of building structures, 309 310 of concrete buildings components concrete moment frame, 311 331 concrete shear walls and concrete frame with infill, 331 340 with experiments and digging results, 89 125, 90t destruction and digging, 90 93 experiments and identification of existing building components, 94 125 report, 71 72

Index

R Radiographic examination, 109 Rapid in situ method, safe soil-bearing capacity by, 602 Rapid qualitative assessment of vulnerability, 125 135 rapid qualification of vulnerability, 134 135 Rapid vulnerability assessment, 306 308 methods for nonstructural components behavior assessment to reach expected performance level, 562 characteristics of nonstructural components, 560 561 checklist for nonstructural component hazards in earthquake, 563 572 samples for complete and qualitative assessment, 562 563 visual inspection, 561 562 Ratio span to depth of beam, 453 Real torsion, 165, 165f Rebound (Schmidt) hammer, 101, 101f, 163f Recrystallization, 78 Refining operations, 604 Regulation standards of seismic analysis over time, 8 12 damage to John Muir School, 11f performance level regulations, 12 prescriptive regulations, 12 Rehabilitation, 2 7, 2f essential rehabilitation to confront decaying effect of time, 5 necessity of time, 6 from perspective of accidents, 5 from perspective of designing buildings against earthquake, 7 prevention of mental disorders and stress, 6 and prevention of postearthquake social damages and crimes, 6 regulation standards of seismic analysis over time, 8 12 retrofitting in civil engineering science, 7 8 strategy, 355 356 in terms of preserving environment, 5 6

663 Rehabilitation method, 634 635, 635f of existing building, three-method for, 72 retrofitting with construction of new restrained building, 629 with existing retain wall and added new buttresses, 630 by increasing wall section, 630 631 with pre post tensioned cables, 628 629 trenches of urban development site, 623f, 624 631, 624f damage to retain walls that prevent trench displacement, 627 foundation-bearing capacity modification, 625 626 instability of downstream trenches of buildings, 625 instability of soil trenches under buildings, 625 problems, 625 seismic rehabilitation methods for existing retain wall, 628 stability of soil slope, 627 trench design in retaining walls, 627 628 trench instability access roads, 625 Reinforced concrete coverings, 357 foundation, 37, 37f shear wall types, 332 333 in-place shear wall, 332 precast shear wall, 332 333 Reinforcement, 2 3, 4f, 100 positions for removing, 124 splice of, 315, 316f Renovation, 2 3 Repair, 2 3, 4f method, 187 Retraction method, 357 Retrofitting, 631f in civil engineering science, 7 8 seismic rehabilitation of existing buildings, 7 8 with construction of restrained building, 629

664 Retrofitting (Continued) with existing retain wall and added new buttresses, 630 by increasing wall section, 630 631 with pre post tensioned cables, 628 629 solutions fully restrained moment connection with bolt or weld, 498 of steel beams with external tension by tensile cable, 497 498 Rigid diaphragm, 17 structure, 303 Rigid spread footing, 31 Rockwell stiffness, 106, 107f Roof brick arched vault roof and floor form, 18 19 in civil engineering, 14 COBIAX, 23 24 compound, 20 concrete slab, 21 23 damages related to roof structures, 200 201, 201f diaphragm, 40 joist-block, 19 prestressed roof slab and floor form, 25 26 steel metal deck, 21 traditional composite, 21 Waffle slab, 23 ROOFIX roof and floor form, 24 25, 25f Rotational stiffness in deep foundation, 353 Rotatory slippage, 58 Rubber separators, 508

S Safe bearing capacity of soil, 601 602, 601f Safety margin, 3 5, 4f, 9f Salts ingress, 76 Sampling stage, 120 122 Schmidt hammer, 102 103 Schmidt Hammer test, 279 SDOF system. See Spectral displacement of one-degree freedom system (SDOF system)

Index

Section area of net mortared/grouted section of wall or pier, 218 Seismic acceleration/gravity ratio, 9 10 Seismic force in vertical distribution method, 161 163 Seismic hazard zone, 135 Seismic isolation systems, 585 Seismic isolators and damper, 363 Seismic lateral and gravity structure main systems, 26 29, 27f building frame system, 28 combined or hybrid system, 29 load bearing wall system, 27 28 simple moment frame system, 28 29 structural systems, 29 Seismic lateral load (V) for linear static analysis, 158 161 Seismic lateral restrained system, 532 533 Seismic loads, 146 for evaluation of nonstructural components, 574 575 analytical procedure, 574 575 prescriptive procedure, 574 Seismic recovery process, 188 Seismic rehabilitation, 2, 589f, 637 acceptance criteria for nonstructural on seismic rehabilitation objective, 578 584 building types in seismic rehabilitation, 39 buildings with concrete materials, 39 buildings with masonry materials, 39 buildings with steel materials, 39 of components in ceiling level, 265 266 in components in story level, 263 265 correction of cracked spots, 263 using FRP fibers, 264 installing concrete shear wall, 264 installing steel brace with new frame, 265 procured of wall shotcrete, 263 retrofitting with vertical and horizontal secondary ties, 263 of concrete building, 310 311, 310f of concrete structures, 308 of connections against damage, 494 499 continuity plates, 494 495

Index

length of end plate and use of hardener, 498 499 retrofitting of steel beams with external tension, 497 498 retrofitting solutions fully restrained moment, 498 seismic rehabilitation of base plate, 499 welding steel connections reinforcement solution, 495 497 and evaluation-bearing capacity of nonstructural components, 586 589 assessed nonstructural components of building, 587t impact of earthquake force, 587f rehabilitation by link between lightweight elements, 586f of existing buildings, 261 262 concrete structure frame buildings, 301 masonry structure buildings, 193 steel structure frame buildings, 437 of foundation, 340 343 in foundation level, 267 indicators and criteria for seismic rehabilitation, 39 54 methods of steel skeleton building, 499 508 building retrofit by seismic separation using base isolation units, 506 508 using dampers, 505 506 executional procedure of compressive and tensile brace, 504 executional procedure of new beam between present columns, 504 using FRP composites, 504 505 improving stiffness for building potential of soft story, 499 501 procedure of adding new braces to existing building, 501 procedure of adding new infill wall to existing frame, 503 504 procedure of retrofitting by adding new column to existing building, 501

665 procedure of retrofitting by adding new shear wall, 502 process, 1 2 and reducing danger of nonstructural components, 584 585, 585f bracing of mechanical and quasimechanical components, 586f rehabilitation and concepts, 2 7 site specifications to investigate threats during, 54 61 for soil of site, 604 623 solution for building, 285 289 advantages and disadvantages of seismic rehabilitation plans, 288 consistency in arch ceilings, 287 288 demolishing volume of executive options, 289 execution cost, 288 execution time, 288 inconveniency for users or temporary suspension of building usage, 289 lateral stiffness, 286 287 required facilities and equipment and skills of local labor, 289 structural steelwork frame buildings, 485 508 structure or building, 354 367 adding extended moment frames, 363 calculation methods for seismic rehabilitation of shallow foundation, 364 using concrete or masonry infill, 359 effective width of foundation, 364 367 using FRP fibers, 362 363 increasing shear capacity of column using cross brace, 361 installing steel/concrete shear wall in concrete existing structures, 357 358 methods of local strengthening, 355 retraction or pretensioning method, 357 using seismic isolators and damper, 363 seismic rehabilitation of concrete ceiling, 360

666 Seismic rehabilitation (Continued) seismic rehabilitation of connections, 361 362 using steel braces, 358 steel jacket usage, 356 357 structure retrofitting and rehabilitations strategy, 355 356 use of concrete jackets or reinforced concrete coverings, 357 techniques, 354 367, 485 508 local seismic rehabilitation of members, 354 types of buildings and constituent elements, 12 39 Seismic retrofitting, 505 Seismic separation, 506 507 Seismic separators, 508 Seismic zone, 135 Seismic zoning maps, 51 Seismic/replacement methods of compaction rehabilitation, 606 Seismicity assessment, 561 Semideep foundations, 34 Semirigid diaphragm, 18 Semiseparate modeling, 348 Separation of concrete particles, 81, 82f load-bearing system, 183 modeling, 348 separating wall, 179 181 analyzing behavior of infill frames, 180 181 Separators, 179 181 Serviceability earthquake, 50 51 Sewage disposal systems, 84 85 Shallow foundation, 30 34, 344 349. See also Drilled shaft foundation balanced-base foundation, 31 32 calculation methods for seismic rehabilitation of, 364 combined foundation, 32 deep foundation, 34 determining capacity by prescriptive analysis, 346 evaluation stiffness parameters on, 346 347 extensive (MAT) foundation, 32 33

Index

and foundation modeling, 347 349 modeling of foundation and soil, 349 pile foundation, 349 semiseparate modeling, 348 separate modeling, 348 simultaneous complete modeling, 349 foundation strength and stiffness, 345 geotechnical conditions, 345 load-bearing capacity, 345 346 of foundations, 345 pad foundation, 31 semideep foundations, 34 strip foundation, 31 structural conditions of foundation, 345 Shear capacity, 215 223 of walls, 216 223 diaphragm rigidity, 216 shear force, 217 steps in calculating, 217 223 Shear expected strength capacity, 111 112 Shear failure in column, 237 Shear force, 15 Shear strength, 317 Shear wall, 302 concrete moment frame in, 304 concrete simple frames with, 303 Shear-centered effect, 137 138 Sheet pile foundation, 34, 34f Shell structures, 437 439 Shelves, 557 558, 581, 583 Short column, 197, 197f, 198f break, 238 Silicates, 84 85 Simple moment frame system, 28 29, 29f Simple slippage, 57 58, 58f Simultaneous complete modeling, 349 Simultaneous impact of earthquake in orthogonal direction, 151, 152f Site against scouring and fluidization phenomena, 631 635 technical specifications of influential elements of existing buildings, 632 633 technical characteristics of site, 633 technical characteristics of soil structure, 633

Index

Site component capacity, computer modeling of, 604 Site effectivity in building performance levels, 593 597 rational behind seismic rehabilitation of site, 597 site on earthquake, 594 597 site properties, 594, 595f scheme of site threat at glance, 595f site effects in Kermanshah earthquake, 596f Site pathology and seismic rehabilitation methods comprehensive assessment of vulnerabilities for soil-bearing capacity, 604 potential damage of site treatment, 598 600 rapid vulnerability for soil-bearing capacity, 601 603 seismic rehabilitation methods for soil of site, 604 623 site effectivity in building performance levels, 593 597 site seismic rehabilitation and identify potential damage, 624 635 Site rehabilitation, 606 Site seismic rehabilitation and identify potential damage building weight, 634, 635t evaluation of soil-bearing capacity, 633 634 mechanical properties required by tests for site soil, 633, 634t rehabilitation method, 634 635 rehabilitation methods trenches of urban development site, 624 631 site against scouring and fluidization phenomena, 631 635 Site specifications in earthquake risk, 374 375 to investigate threats during seismic rehabilitation, 54 61 differential settlement, 56 draught water forces, 59 fault risk, 55 faults distance from of site, 55

667 landslide, 60 61 lateral spread and sequential fracture, 59 60 liquefaction history, high subsidence, 55 56 liquescence phenomenon, 57 progressive/further liquefaction of soil, 56 slipping phenomenon and slip types of mountain range, 57 59 talus slope slippage, 60 type of land and underground water surface, 61 Site treatment, potential damage of, 598 600 damages that lead to rehabilitation of subsoil, 600 instability of downstream trenches of buildings, 598 instability of trenches under building’s foundation, 598 soil foundation capacity modification under foundation, 599 soil liquefaction, 600 trench instability of access roads, 599 Slab foundation, 32 Slab roof without support beam, 23, 23f Slab-column moment frame, 324, 330 331. See also Beam-column, concrete moment frames Slab-column moment frames, 312, 318 Slenderness effects in acceptance criteria, 453 454 Sliding shear failure mode, 237 strength, 246 247 Slip types of mountain range, 57 59 Slipping phenomenon and slip types of mountain range, 57 59 Soft or weak story strength of building, 213 Software, modeling components in, 173 Soil corrosion steel buried in, 86, 86f and foundation, 380 foundation capacity modification under foundation, 599 600

668 Soil (Continued) instability of soil trenches under buildings, 625, 626f liquefaction, 55 56 mixing, 613, 614f piling methods in, 617 618 shoring with piling, 617 slope stability, 627, 628t technical characteristics of soil structure, 633 vibratory method, 607 Soil and rock, grouting methods in, 610 613, 610f chemical grouting, 611 compaction grouting in soil, 611 612 fissure grouting, 612 high-pressure grouting, 613 permeation grouting in soil, 610 611 Soil and structure interaction, 150, 150f analyzing interaction of soil and structure, 150, 151f Soil compaction in construction industry, 606, 606f process, 605 606 Soil of site, seismic rehabilitation methods for, 604 623, 605f compaction stages, 607 density of soil, 605 606 dynamic compaction, 607 608 methods of piling in soil, 617 618 micropiles, 618 623 nailing in soil, 614 616 preloading, 609 seismic rehabilitation with grouting, 609 613 seismic/replacement methods of compaction rehabilitation, 606 site rehabilitation, 606 soil compaction in construction industry, 606 soil mixing, 613 soil shoring with piling, 617 stone and soil anchoring, 617 underground walls for controlling water level, 613 614 Soil-bearing capacity, 599 602, 602f

Index

comprehensive assessment of vulnerabilities, 604 evaluation of, 633 634 rapid vulnerability example, 603, 603f, 603t safe bearing capacity of soil, 601 602, 601f testing determination of safe soilbearing capacity, 602 weight loss method, 602 Spectral displacement of one-degree freedom system (SDOF system), 171 Spectrum analysis method, 53 of specific site design, 51 52 Square-based pyramid, 106 Stability coefficient, 161 Staircase, 580 Standard design spectrum, 51 Static linear method, 333 336 acceptance criteria for components, 335 336, 337t determining stiffness of components, 333 334 determining strength of components, 334 nominal shear strength of shear walls, 334 335 Static nonlinear analysis method, 336 340 coupling beams, 336, 339f determining stiffness of components, 336 foundation, 340 354 Steel braces, 358 concentric braced frame, 474 475 stiffness of components for CBF brace, 474 strength of CBF brace, 474 475 decks, 15 eccentric braced frames, 475 foundation, 36, 37f jacket usage, 356 357, 358f joist or section with I shape profile, 124 125, 125f members, 279 metal deck roof, 21, 22f

Index

moment frames, 443 472 outside building structure, 83 84, 84f plates shear wall, 479 484 acceptance criteria, 484 stiffness for shear wall, 482 strength of steel shear wall, 482 484 steel structure, designing error in, 87 strength evaluation, 104 110 Steel materials buildings with, 39 pathology in, 83 87 corrosion, 83 86 designing error in steel structure, 87 fire in steel construction, 87 Steel structure frame buildings, 437 440 comprehensive assessment of vulnerabilities for existing building, 442 484 brace frame, 472 479 specifications of materials, 442 steel moment frames, 443 472 steel plates shear wall, 479 484 tests, 443 framed structures, 438 potential structural damage, 440 441 rapid vulnerability assessment, 442 real case study example, 508 551 seismic rehabilitation techniques, 485 508 shell structures, 438 439 suspension structures, 440 truss structures, 440 Stepped ceilings and soffit/intrados coverings, 568 Stepped floors, 581 Stiffness, 137 139, 137t, 138f, 257 258 of components, 313 314, 314t, 444 445 of masonry infill, 243 246 in linear method, 138 within nonlinear behavior range of materials, 245 246 in nonlinear method, 138 139 parameters using for, 244t within range of linear behavior of materials, 243 245 for shear wall, 482

669 stiffness-centered effect, 137 138 Stone and soil anchoring, 617, 617f Stone foundation, 35, 36f Strength of material, 142 143, 258 capacity of structural components, 142 143 in components, 142 of masonry infill, 246 260 acceptance criteria, 249 260 corner failure strength, 247 248 interfacial strength in linear and nonlinear behavior range of materials, 248 sliding shear strength, 246 247 of steel shear wall, 482 484 Strip foundation, 31, 32f Structural components, 555 556 action control, 140 141 controlled by deformation, 140 141 controlled by force, 141 Structural connection components, 71 Structural function number, 46 Structural oscillation, fundamental period of, 155 158 Structural performance level of collapse occupancy, 47 49 of immediate occupancy, 46 of life safety, 47 Structural roof, 14 26 diaphragm, 14 18 types of roof, 18 26 Structural steelwork frame buildings, seismic rehabilitation of, 485 508 steel sections, 486 508 column and beam, 487 489 damage to connection in steel structures, 490 493 seismic rehabilitation methods of steel skeleton building, 499 508 seismic rehabilitation of connections against damage, 494 499 Structural systems, 29, 30f Structural wall, 179 damages related to, 197 198 cracks in masonry wall, 199f lintel and tie in masonry building, 199f

670 Structural wall (Continued) opening problem in wall, 198f Structure analysis methods, 52 54, 52f linear methods, 52 53 nonlinear methods, 54 Structure retrofitting, 355 356 Structure wall and infill panels, 179 184 Sulfate attacks, 78, 79f Surface restoration cases, 124 Suspension structures, 437, 440

T Tabriz historical masonry building, 193 194, 194f Talus slope slippage, 60, 61f Target displacement calculation for rehabilitated structures, 420 421 Target relocation, 420 Telecommunication equipment, 583 system, 557 558 Temporary molding, 20 10-story steel special moment frame building 1 center brace frame, 508 551 ceiling structure and function, 513 foundation structure type, 513 qualities evaluations for existing building, 514 525 building configuration, 517 519 construction site of current building, 516 evaluating consistency of building, 514 evaluating opening areas within diaphragm, 515 evaluating regularity in height of existing structure and plan, 514 evaluating symmetry condition in plan, 514 515 existing deterioration, decay, recession, 515 expected and lower bound strength of material, 519 extract and present analysis results, 524 foundation modeling, 521 gravity load, 520

Index

integration and consistency in accessible areas, 515 methods, 524 primary and secondary components, 520 primary controls of building structure, 521 quantitative vulnerability of floors, 516 seismic evaluation parameters of building vulnerability, 522 523 seismic rehabilitation by changing stairway location, 525 seismic rehabilitation of long cantilevers and façade components, 525 seismic rehabilitation plan, 524 525 soil and foundation, 519 tests and digging, 516 valuating height to dimensions of building, 515 structural system, 511 512 fully special restrained steel moment frame, 511 512 partially restrained steel moment frame, 512 partially restrained steel moment frame 1 infill concrete shear walls, 513 Tensile strength in bending, 240 Tension test, 104 105, 105f Thermal and cooling installations, 582, 582f, 586f Thermography test, 110 Three-story concrete moment frame building with semirigid diaphragm, 368 396. See also Two-story reinforced masonry building seismic rehabilitation steps for project, 369 396 basic controls of building structures, 382 383 binary force linear behavior model, 394 combined gravity and lateral loading, 383 384 comparing options, 395 396

Index

comparison of foundation rehabilitation for upper methods, 390 391 control of nonlinear structural analysis results, 384 defining gravity load, 381 descriptive evaluation of buildings needs for rehabilitation, 381 determining lateral stiffness required for building, 386 387 determining main structural and nonstructural components, 382 digging and tests, 375 380 evaluation of nonlinear structure response, 385 evaluation of underlying soil compatibility, 386 fixing or reducing irregularities in the existing building, 386 foundation evaluation and analysis, 385 386 foundation modeling, 382 foundation rehabilitation, 394 395 increase stiffness of building, 387 increasing stiffness of building by incorporating shear walls, 388 increasing stiffness of system, 388 389 increasing strength by adding shear walls, 387 388 nonlinear analysis for final seismic rehabilitation method, 392 393 nonlinear vulnerability assessment, 383 preparation of primary methods of seismic rehabilitation, 386 qualitative evaluation of regularity in height, 373 375 qualitative evaluation of regularity in plan, 372 qualitative vulnerability assessment, 370 372 relative comparison of costs, 396 selecting analysis model, 381 Time history analysis method, 53 Time-consuming execution, 24 Torsion, 164 166, 164f, 165f strength, 317 Track impact, 593 594

671 Traditional masonry buildings, 194 195 with adobe material, 196f evaluation and identification of defects in, 210 211 connection of structural components, 211 defects in load-bearing walls, 210 defects of materials used in building, 210 defects of structural system of building, 210 diaphragm of ceiling, 211 nonstructural elements of masonry materials, 211 with stone materials, 195f Traditional masonry materials, pathology in, 88 89 Transferring slippage, 57 58, 58f Transverse reinforcement, 139 140 Trapezoidal galvanized sheets, 21 Trench design in retaining walls, 627 628, 628f Trench instability of access roads, 599, 599f access roads, 625, 626f Trenches under building’s foundation instability, 598, 599f Truss structures, 438, 440 22-story concrete moment frame building, 396 435 analysis average PMM stress of columns on floors, 414 effect of component stiffness on structure stiffness, 413 414 output results from computer modeling, 413 results for soil stress, 432 building in current status, 406 407 calculation connection profile of crucifix and concrete column, 423 424 number of shear-head components needed, 424 comparison of two behaviors of mixed columns, 427 430

672 22-story concrete moment frame building (Continued) conclusions from foundation examination, 435 controlling transfer of steel column shear to concrete bottom column, 424 designing steel cantilever for new concept changes, 425 426 destructive part specification, 409 determination basic level for basic shear of applying earthquake level, 406 concrete material specifications, 404 405 figure of building, 404 material specification, 404 steel material specifications, 405 diaphragm stiffness considering slab on cement block and joist, 417 418 evaluation of soil and foundation of structure, 432 examination effects of P Δ, 407 structure weight, 408 visible defects of building, 402 404 existing building architecture specifications, 402 relate to new floors and new elements of building facade, 422 structure specifications, 402 expected soil capacity, 430 431 explaining results from seismic separation analysis, 414 415 final analysis of structure through nonlinear method, 418 419 foundation evaluation, 431 structure evaluation, 432 general characteristics of floors, 401 402 interpretation of result of evaluating nonlinear static analysis, 421 422 introducing seismic rehabilitation objective for building, 404 investigation of foundation structure, 433 434 of metal jacket design for vulnerable columns, 426 427

Index

key recommendation, 408 modeling existing foundation, 431 materials, elements, and components, 419 421 part I of seismic rehabilitation studies, 401 practical example, 396 399 process of seismic rehabilitation studies, 400 qualitative assessment of example, 399 400 results of analyzing and evaluating computer modeling, 407 408 of foundation analysis, 432 sample analysis of vulnerability on first floor, 414 solution recommended to increase number of floors, 408 specifications for attached structure, 409 status of technical documents, 404 steel structure part of project, 411 413 steps to seismic rehabilitation in project, 416 417 strengthen seismic system and installing secondary system, 409 411 Two-story reinforced masonry building, 268 290. See also Three-story concrete moment frame building with semirigid diaphragm digging and experiments, 273 281 practical example, 268 qualitative vulnerability evaluation, 268 273 building’s components cohesion, 272 evaluation of changes in existing building plan, 273 executive weaknesses in components and connections, 271 general specifications of site, 273 geometric properties of building, 269 gravity and lateral load structure, 272 273 knowledge factor, 270 271 qualitative investigation of minimum shear strength, 270

673

Index

ratio of height to width and length dimensions of building, 269 roof system and building structure, 269 status of openings and proximity to floor diaphragm, 272 symmetry status of building plans, 272 rapid qualification of vulnerability, 273

U Ultrasonic experimenting, 103 Ultrasonic pulse velocity (UPV), 103 104, 103f Ultrasonic pulse wave velocity. See Ultrasonic experimenting Ultrasound test, 109 Underground walls for controlling water level, 613 614, 615f Underground water surface, 61 Uniform distribution type 2, 145 Unreinforced masonry material, 111 112 UPV. See Ultrasonic pulse velocity (UPV) Urban development site, rehabilitation methods trenches of, 624 631

V Variable distribution, 145 Vertical bracing, 474 Vertical component effect of earthquake, 151 Vertical distribution method, seismic force in, 161 163 Vickers stiffness, 106, 107f Visual assessment of quality of materials, 75 89 pathology in concrete materials, 76 82 in steel materials, 83 87 in traditional masonry materials, 88 89 Visual inspection, 561 562 Vulnerability comprehensive assessment of, 308 354 of existing buildings, 125 185 comprehensive and detailed vulnerability assessment, 135 185

rapid qualitative assessment of vulnerability, 125 135, 137t methods for analyzing nonstructural component, 573 577 of shear capacity of floor, 218 vulnerable wall detection, 284 285 Vulnerability assessment chords and collectors in diaphragm, 173 178 earthquake vertical effects, 185 effective parameters and operations, 135 152 integration of building parts, 182 184 introduction to analysis methods linear analysis methods, 152 169 modeling components in software, 173 nonlinear analysis, 169 173 out-of-plane strength, 181 182 structure wall and infill panels, 179 184

W Waffle slab, 23, 24f Wall(s), 179, 179f, 580 density control, 227 228 height control, 227 strength in linear method, 219 222 strength in nonlinear method, 222 Warehouses, 164 Water cycle, 62f heaters, 582 583 pipes, 86 Weight loss method, 602 Welding disadvantages and defects of, 491 steel connections reinforcement solution, 495 497 Wet concrete, 79 Wind loads, 146 Windows, 569 Wood, 580 Wooden joists, 19

X X-rays, 109