Understand the complexities and challenges of retrofitting building infrastructure
Across the world, buildings are gradually becoming structurally unsound. Many were constructed before seismic load capacity was a mandatory component of building standards, and were often built with low-quality materials or using unsafe construction practices. Many more are simply aging, with materials degrading, and steel corroding. As a result, efforts are ongoing to retrofit existing structures, and to develop new techniques for assessing and enhancing seismic load capacity in order to create a safer building infrastructure worldwide.
Seismic Retrofit of Existing Reinforced Concrete Buildings provides a thorough book-length discussion of these techniques and their applications. Balancing theory and practice, the book provides engineers with a broad base of knowledge from which to approach real-world seismic assessments and retrofitting projects. It incorporates knowledge and experience frequently omitted from the building design process for a fuller account of this critical engineering subfield.
Seismic Retrofit of Existing Reinforced Concrete Buildings readers will also find: - Detailed treatment of each available strengthening technique, complete with advantages and disadvantages - In-depth guidelines to select a specific technique for a given building type and/or engineering scenario - Step-by-step guidance through the assessment/retrofitting process
Seismic Retrofit of Existing Reinforced Concrete Buildings is an ideal reference for civil and structural engineering professionals and advanced students, particularly those working in seismically active areas.
Table of Contents
Foreword by Rui Pinho xvii
Acknowledgments xvix
1 Introduction 1
1.1 General 1
1.2 Why Do Old RC Buildings Need Strengthening? 3
1.3 Main Differences Between Assessment and Design Methodologies 4
1.4 Whom Is this Book For? 7
1.5 Main Standards for the Seismic Evaluation of Existing Structures 8
References 12
2 Know Your Building: The Importance of Accurate Knowledge of the Structural Configuration 15
2.1 Introduction 15
2.2 What Old RC Buildings Are Like 16
2.2.1 Lack of Stirrups 17
2.2.2 Unconventional Reinforcement in the Members 18
2.2.3 Large, Lightly Reinforced Shear Walls or Lack of Shear Walls 19
2.2.4 Lap Splices 22
2.2.5 Corrosion 22
2.2.6 Geometry: Location of Structural Members 25
2.2.7 Geometry: Bad Alignment of the Columns 25
2.2.8 Geometry: Arbitrary Alterations During Construction or During the Building’s Lifetime 26
2.2.9 Bad Practices with Respect to the Mechanical and Electrical Installations 26
2.2.10 Soft Ground Stories 28
2.2.11 Short Columns 28
2.2.12 Different Construction Methods 30
2.2.13 Foundation Conditions 30
2.2.14 Discussion 32
2.2.15 One Final Example 34
2.3 How Come Our Predecessors Were So Irresponsible? 34
2.4 What the Codes Say - Knowledge Level and the Knowledge Factor 36
2.5 Final Remarks 39
References 39
3 Measurement of Existing Buildings, Destructive and Nondestructive Testing 41
3.1 Introduction 41
3.2 Information Needed for the Measured Drawings 41
3.3 Geometry 44
3.4 Details - Reinforcement 46
3.5 Material Strengths 52
3.6 Concrete Tests - Destructive Methods 54
3.7 Concrete Tests - Nondestructive Methods, NDT 55
3.7.1 Rebound Hammer Test 56
3.7.2 Penetration Resistance Test 56
3.7.3 Pull-Off Test 57
3.7.4 Ultrasonic Pulse Velocity Test, UPV 57
3.8 Steel Tests 58
3.9 Infill Panel Tests 58
3.10 What Is the Typical Procedure for Monitoring an Existing Building? 59
3.11 Final Remarks 61
References 62
4 Methods for Strengthening Reinforced Concrete Buildings 63
4.1 Introduction 63
4.2 Literature Review 64
4.3 Reinforced Concrete Jackets 67
4.3.1 Application 67
4.3.2 Advantages and Disadvantages 74
4.3.3 Design Issues: Modeling, Analysis, and Checks 76
4.4 Shotcrete 77
4.4.1 Introduction 77
4.4.2 Dry Mix vs. Wet Mix Shotcrete 79
4.4.3 Advantages and Disadvantages of Shotcrete 80
4.4.4 What Is It Actually Called - Shotcrete or Gunite? 81
4.4.5 Materials, Proportioning, and Properties 81
4.4.5.1 Cement 81
4.4.5.2 Pozzolans 82
4.4.5.3 Silica Fume 82
4.4.5.4 Aggregates 82
4.4.5.5 Water 83
4.4.5.6 Fiber Reinforcement 83
4.4.5.7 Chemical Admixtures and Accelerators 85
4.4.5.8 Reinforcing Steel 85
4.4.6 Mix Proportions for the Dry-Mix Process 85
4.4.7 Equipment and Crew 86
4.4.7.1 Dry-Mix Process 86
4.4.7.2 Wet-Mix Process 87
4.4.8 Curing and Protection 87
4.4.9 Testing and Evaluation 88
4.5 New Reinforced Concrete Shear Walls 89
4.5.1 Application 89
4.5.2 Foundation Systems of New Shear Walls 97
4.5.3 Advantages and Disadvantages 98
4.5.4 Design Issues: Modeling and Analysis 98
4.6 RC Infilling 99
4.6.1 Application 99
4.6.2 Advantages and Disadvantages 100
4.7 Steel Bracing 101
4.7.1 Application 101
4.7.2 Advantages and Disadvantages 105
4.7.3 Design Issues: Modeling, Analysis, and Checks 106
4.8 Fiber-Reinforced Polymers (FRPs) 106
4.8.1 FRP Composite Materials 106
4.8.2 FRP Composites in Civil Engineering and Retrofit 107
4.8.3 FRP Composite Materials 109
4.8.4 FRP Wrapping 110
4.8.5 FRP Laminates 115
4.8.6 Near Surface Mounted FRP Reinforcement 119
4.8.7 FRP Strings 120
4.8.8 Sprayed FRP 122
4.8.9 Anchoring Issues 123
4.8.10 Advantages and Disadvantages of FRP Systems 123
4.8.11 Design Issues 125
4.9 Steel Plates and Steel Jackets 127
4.9.1 Advantages and Disadvantages 130
4.9.2 Design Issues 131
4.10 Damping Devices 131
4.11 Seismic Isolation 133
4.11.1 Type of Base Isolation Systems 136
4.11.2 Advantages and Disadvantages 138
4.11.3 Design Issues 138
4.12 Selective Strengthening and Weakening Through Infills 139
4.13 Strengthening of Infills 141
4.13.1 Glass or Carbon FRPs 142
4.13.2 Textile Reinforced Mortars TRM 143
4.13.3 Shotcrete 145
4.14 Connecting New and Existing Members 145
4.14.1 Design Issues 147
4.15 Strengthening of Individual Members 148
4.15.1 Strengthening of RC Columns or Walls 148
4.15.2 Strengthening of RC Beams 149
4.15.3 Strengthening of RC Slabs 153
4.15.4 Strengthening of RC Ground Slabs 154
4.16 Crack Repair - Epoxy Injections 157
4.17 Protection Against Corrosion, Repair Mortars, and Cathodic Protection 158
4.18 Foundation Strengthening 160
4.19 Concluding Remarks Regarding Strengthening Techniques 163
4.20 Evaluation of Different Seismic Retrofitting Solutions: A Case Study 164
4.20.1 Building Configuration 164
4.20.2 Effects of the Infills on the Structural Behavior 170
4.20.3 Strengthening with Jacketing 175
4.20.4 Strengthening with New RC Walls (Entire Building Height) 177
4.20.5 Strengthening with New RC Walls (Ground Level Only) 182
4.20.6 Strengthening with Braces 189
4.20.7 Strengthening with FRP Wrapping 192
4.20.8 Strengthening with Seismic Isolation 195
4.20.9 Comparison of the Methods 198
References 200
5 Criteria for Selecting Strengthening Methods - Case Studies 221
5.1 Things Are Rarely Simple 221
5.2 Criteria for Selecting Strengthening Method 222
5.3 Basic Principles of Conceptual Design 224
5.4 Some Rules of Thumb 226
5.5 Case Studies 231
5.5.1 Case Study 1: Seismic Upgrade of a Five-Story Hotel 232
5.5.2 Case Study 2: Seismic Upgrade of a Four-Story Hotel 236
5.5.3 Case Study 3: Seismic Upgrade of a Four-Story Hotel 237
5.5.4 Case Study 4: Seismic Upgrade of a Three-Story Residential Building 241
5.5.5 Case Study 5: Seismic Upgrade of a Three-Story Residential Building for the Addition of Two New Floors 241
5.5.6 Case Study 6: Seismic Strengthening of an 11-Story Building 244
5.5.7 Case Study 7: Seismic Strengthening of a Five-Story Building 247
5.5.8 Case Study 8: Seismic Strengthening of a Three-Story Building 247
5.5.9 Case Study 9: Strengthening a Building Damaged by a Severe Earthquake 248
5.5.10 Case Study 10: Strengthening of an 11-Story Building 251
5.5.11 Case Study 11: Strengthening of a Two-Story Building with Basement 253
5.5.12 Case Study 12: Strengthening of a Weak Ground Story with FRP Wraps 255
5.5.13 Case Study 13 (Several Examples): Strengthening of RC Slabs 257
5.5.14 Case Study 14: Strengthening of a Ground Slab 260
5.5.15 Case Study 15: Strengthening of Beam That Has Failed in Shear 260
5.5.16 Case Study 16: Demolition and Reconstruction of a RC Beam 260
5.5.17 Bonus Case Study 1: Strengthening of an Industrial Building 261
5.5.18 Bonus Case Study 2: Strengthening of an Industrial Building 262
5.5.19 Bonus Case Study 3: Strengthening of a Residential Building 263
References 268
6 Performance Levels and Performance Objectives 269
6.1 Introduction 269
6.1.1 Selection of Performance Objectives in the Design of New Buildings 269
6.1.2 Selection of Performance Objectives in the Assessment of Existing Buildings 270
6.2 Seismic Assessment and Retrofit Procedures 270
6.2.1 Seismic Assessment Procedures 270
6.2.2 Seismic Retrofit Procedures 271
6.3 Understanding Performance Objectives 272
6.3.1 Target-Building Performance Levels 272
6.3.1.1 Structural Performance Levels 273
6.3.1.2 Nonstructural Performance Levels 276
6.3.1.3 Target Building Performance Levels 279
6.3.2 Seismic Hazard Levels 280
6.3.3 Performance Objectives 282
6.3.4 Eurocode 8, Part 3, and Other Standards 284
6.3.5 The Rationale for Accepting a Lower Performance Level for Existing Buildings 286
6.4 Choosing the Correct Performance Objective 287
References 289
7 Linear and Nonlinear Methods of Analysis 291
7.1 Introduction 291
7.2 General Requirements 294
7.2.1 Loading Combinations 294
7.2.2 Multidirectional Seismic Effects 295
7.2.3 Accidental Torsional Effects 295
7.3 Linear Static Procedure 296
7.4 Linear Dynamic Procedure 296
7.5 Nonlinear Structural Analysis 298
7.5.1 Nonlinear Structural Analysis in Engineering Practice 298
7.5.2 Challenges Associated with Nonlinear Analysis 300
7.5.3 Some Theoretical Background 301
7.5.3.1 Introduction 301
7.5.3.2 Sources of Nonlinearity 301
7.5.3.3 Solving Nonlinear Problems in Structural Analysis 302
7.5.3.4 Convergence Criteria 305
7.5.3.5 Numerical Instability, Divergence, and Iteration Prediction 306
7.5.4 Implications from the Basic Assumptions of Nonlinear Analysis 307
7.5.5 How Reliable Are Numerical Predictions from Nonlinear Analysis Methods? 309
7.5.6 Final Remarks on Nonlinear Analysis 310
7.6 Nonlinear Static Procedure 311
7.6.1 Pushover Analysis 311
7.6.2 Information Obtained with Pushover Analysis 312
7.6.3 Theoretical Background on Pushover Analysis 313
7.6.4 Target Displacement 314
7.6.5 Applying Forces vs. Applying Displacements 316
7.6.6 Controlling the Forces or the Displacements 317
7.6.6.1 Load Control 317
7.6.6.2 Response Control 318
7.6.7 Control Node 318
7.6.8 Lateral Load Patterns 319
7.6.9 Pushover Analysis Limitations 319
7.7 Nonlinear Dynamic Procedure 320
7.7.1 Information Obtained with Nonlinear Dynamic Analysis 322
7.7.2 Selecting and Scaling Accelerograms 322
7.7.2.1 Natural Scaled and Matched Accelerograms 324
7.7.2.2 Artificial and Synthetic Accelerograms 326
7.7.3 Advantages and Disadvantages of Nonlinear Dynamic Analysis 327
7.8 Comparative Assessment of Analytical Methods 328
7.8.1 Advantages and Disadvantages of the Analytical Methods 328
7.8.2 Selection of the Best Analysis Procedure for Structural Assessment 329
References 330
8 Structural Modeling in Linear and Nonlinear Analysis 333
8.1 Introduction 333
8.2 Mathematical Modeling 333
8.3 Modeling of Beams and Columns 334
8.3.1 Material Inelasticity 334
8.3.2 Geometric Nonlinearities 336
8.3.3 Modeling of Structural Frame Elements 337
8.3.3.1 Concentrated Plasticity Elements 338
8.3.3.2 Advantages and Disadvantages of Concentrated Plasticity Models 339
8.3.3.3 Distributed Plasticity Elements - Fiber Modeling 339
8.3.3.4 Types of Distributed Plasticity Elements 340
8.3.3.5 Advantages and Disadvantages of Distributed Plasticity Models 341
8.3.3.6 Considerations Regarding the Best Frame Model for Structural Members 342
8.4 Modeling of Shear Walls 344
8.5 Modeling of Slabs 345
8.6 Modeling of Stairs 347
8.7 Modeling of Infills 348
8.7.1 A Simple Example: Infilled Frame vs. Bare Frame 349
8.7.2 Another Example: Partially Infilled Frame (Soft Story) vs. Bare Frame 351
8.7.3 Problems in the Modeling of Infills 354
8.8 Modeling of Beam-Column Joints 356
8.9 Modeling of Bar Slippage 358
8.10 Shear Deformations 359
8.11 Foundation Modeling 359
8.12 How Significant Are Our Modeling Decisions? 359
References 360
9 Checks and Acceptance Criteria 363
9.1 Introduction 363
9.2 Primary and Secondary Members 364
9.3 Deformation-Controlled & Force-Controlled Actions 365
9.4 Expected Vs. Lower-Bound Material Strengths 366
9.5 Knowledge Level and Knowledge Factor 368
9.6 Capacity Checks 369
9.6.1 Capacity Checks for Linear Methods - ASCE 41 369
9.6.1.1 Component Demands 369
9.6.1.2 Component Capacities 370
9.6.2 Capacity Checks for Nonlinear Methods - ASCE 41 372
9.6.2.1 Component Demands 372
9.6.2.2 Component Capacities 372
9.6.3 Capacity Checks for Linear Methods - Eurocode 8, Part 3 372
9.6.3.1 Component Demands 372
9.6.3.2 Component Capacities 372
9.6.4 Capacity Checks for Nonlinear Methods - Eurocode 8, Part 3 374
9.6.4.1 Component Demands 374
9.6.4.2 Component Capacities 374
9.7 Main Checks to Be Carried Out in an Assessment Procedure 374
9.7.1 Bending Checks 375
9.7.1.1 Eurocode Framework (EC8: Part 1 and EC8: Part 3) - Nonlinear Methods 375
9.7.1.2 US Framework (ASCE 41 and ACI 318) - Nonlinear Methods 376
9.7.2 Shear Checks 376
9.7.2.1 Eurocodes Framework (EC8, Part 1, and EC8, Part 3) 376
9.7.2.2 US Framework (ASCE 41 and ACI 318) 378
9.7.3 Beam-Column Joints 378
References 378
10 Practical Example: Assessment and Strengthening of a Six-Story RC Building 381
10.1 Introduction 381
10.2 Building Description 381
10.3 Knowledge of the Building and Confidence Factor 383
10.3.1 Geometry 383
10.3.2 Reinforcement 383
10.3.3 Material Strengths 384
10.4 Seismic Action and Load Combinations 386
10.5 Structural Modeling 387
10.6 Eigenvalue Analysis 391
10.7 Nonlinear Static Procedure 393
10.7.1 Lateral Load Patterns 393
10.7.2 Selection of the Control Node 394
10.7.3 Capacity Curve and Target Displacement Calculation 394
10.7.4 Safety Verifications 398
10.7.5 Chord Rotation Checks 398
10.7.6 Example of the Calculation of Chord Rotation Capacity 399
10.7.7 Shear Checks 400
10.7.8 Example of the Calculation of Shear Capacity 401
10.7.9 Beam-Column Joint Checks 403
10.7.10 Example of the Checks for Beam-Column Joints 403
10.8 Strengthening of the Building 406
10.8.1 Strengthening with Jackets 406
10.8.2 Designing the Interventions 407
10.8.3 Deliverables 415
10.8.4 Strengthening with Shear Walls 415
References 421
Appendix A Standards and Guidelines 423
A.1 Eurocodes 423
A.1.1 Performance Requirements 423
A.1.1.1 Limit State of Near Collapse (NC) 423
A.1.1.2 Limit State of Significant Damage (SD) 423
A.1.1.3 Limit State of Damage Limitation (DL) 423
A.1.2 Information for Structural Assessment 424
A.1.2.1 KL1: Limited Knowledge 424
A.1.2.2 KL2: Normal Knowledge 424
A.1.2.3 KL3: Full Knowledge 425
A.1.2.4 Confidence Factors 425
A.1.3 Safety Factors 425
A.1.4 Capacity Models for Assessment and Checks 425
A.1.4.1 Deformation Capacity 425
A.1.4.2 Shear Capacity 428
A.1.4.3 FRP Wrapping 429
A.1.5 Target Displacement Calculation in Pushover Analysis 429
A.1.5.1 Transformation to an Equivalent Single Degree of Freedom (SDOF) System 430
A.1.5.2 Determination of the Idealized Elasto-Perfectly Plastic Force-Displacement Relationship 430
A.1.5.3 Determination of the Period of the Idealized Equivalent SDOF System 431
A.1.5.4 Determination of the Target Displacement for the Equivalent SDOF System 431
A.1.5.5 Determination of the Target Displacement for the MDOF System 432
A.2. ASCE 41-17 432
A.2.1 Performance Requirements 432
A.2.1.1 Performance Level of Operational Level (1-A) 433
A.2.1.2 Performance Level of Immediate Occupancy (1-B) 433
A.2.1.3 Performance Level of Life Safety (3-C) 433
A.2.1.4 Performance Level of Collapse Prevention (5-D) 433
A.2.2 Information for Structural Assessment 433
A.2.2.1 Minimum Knowledge 434
A.2.2.2 Usual Knowledge 434
A.2.2.3 Comprehensive Knowledge 434
A.2.3 Safety Factors 434
A.2.4 Capacity Models for Assessment and Checks 434
A.2.4.1 Deformation Capacity 435
A.2.4.2 Shear Capacity 435
A.2.4.3 FRP Wrapping 441
A.2.5 Target Displacement Calculation in the Nonlinear Static Procedure 441
A.2.5.1 Determination of the Idealized Elasto-Perfectly Plastic Force-Displacement Relationship 443
A.2.5.2 Determination of the Fundamental Period 444
References 444
Appendix B Poor Construction and Design Practices in Older Buildings 445
B.1 Stirrup Spacing 445
B.2 Lap Splices 445
B.3 Member Alignment 445
B.4 Pipes inside RC Members 445
B.5 Bad Casting of Concrete 449
B.6 Footings 449
Appendix C Methods of Strengthening 455
C.1 Reinforced Concrete Jackets 455
C.2 New Shear Walls 465
C.3 Fiber-Reinforced Polymers 468
C.3.1 FRP Wrapping of Columns 468
C.3.2 FRP Fabrics in Slabs 473
C.3.3 FRP Wraps for Shear Strengthening 473
C.3.4 FRP Laminates 476
C.3.5 FRP Strings 482
C.4 Steel Braces 485
C.5 Steel Jackets 487
C.6 Steel Plates 488
C.7 Infills 491
C.8 Foundations 493
C.9 Dowels and Anchorages 500
C.10 Demolition with Concrete Cutting 502
C.11 Reinforcement Couplers 506
C.12 Epoxy
Injections 507
Index 509
