Chapter 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? 6
1.5 Main Standards for the Seismic Evaluation of Existing Structures 7
1.6 References 10
Chapter 2 Know Your Building: The importance of accurate knowledge of the structural configuration 12
2.1 Introduction 12
2.2 What Old RC Buildings are like 12
2.2.1 Lack of Stirrups 14
2.2.2 Unconventional Reinforcement in the Members 15
2.2.3 Large, Lightly Reinforced Shear Walls or Lack of Shear Walls 16
2.2.4 Lap Splices 16
2.2.5 Corrosion 17
2.2.6 Geometry: Location of Structural Members 18
2.2.7 Geometry: Bad Alignment of the Columns 18
2.2.8 Geometry: Arbitrary Alterations during Construction or during the Lifetime of the Building 18
2.2.9 Bad Practices with respect to the Mechanical and Electrical Installations 19
2.2.10 Soft Ground Storeys 20
2.2.11 Short Columns 20
2.2.12 Different Construction Methods 21
2.2.13 Foundation Conditions 22
2.2.14 Discussion 22
2.2.15 One Final Example 24
2.3 How come our Predecessors were so Irresponsible? 25
2.4 What the Codes say - Knowledge Level and the Knowledge Factor 26
2.5 Final Remarks 29
2.6 References 30
Chapter 3 Measurement of Existing Buildings, Destructive and Non-destructive Testing 31
3.1 Introduction 31
3.2 Information needed for the measured drawings 31
3.3 Geometry 34
3.4 Details - Reinforcement 36
3.5 Material Strengths 39
3.6 Concrete Tests – Destructive Methods 40
3.7 Concrete Tests – Non-destructive Methods, NDT 41
3.7.1 Rebound Hammer Test 41
3.7.2 Penetration Resistance Test 42
3.7.3 Pull-off Test 42
3.7.4 Ultrasonic Pulse Velocity Test, UPV 43
3.8 Steel Tests 43
3.9 Infill Panel Tests 44
3.10 What is the Typical Procedure for Monitoring an Existing Building? 44
3.11 Final Remarks 47
3.12 References 47
Chapter 4 Methods for Strengthening Reinforced Concrete Buildings 49
4.1 Introduction 49
4.2 Literature Review 50
4.3 Reinforced Concrete Jackets 53
4.3.1 Application 53
4.3.2 Advantages and Disadvantages 55
4.3.3 Design Issues: Modelling, Analysis and Checks 56
4.4 Shotcrete 57
4.4.1 Introduction 57
4.4.2 Dry mix vs. Wet mix Shotcrete 58
4.4.3 Advantages and Disadvantages of Shotcrete 59
4.4.4 What is it actually called, Shotcrete or Gunite? 60
4.4.5 Materials, Proportioning, and Properties 61
4.4.6 Mix Proportions for the Dry-mix Process 64
4.4.7 Equipment and Crew 65
4.4.8 Curing and Protection 67
4.4.9 Testing and Evaluation 67
4.5 New Reinforced Concrete Shear Walls 67
4.5.1 Application 67
4.5.2 Foundation Systems of new Shear Walls 70
4.5.3 Advantages and Disadvantages 71
4.5.4 Design Issues: Modelling and Analysis 72
4.6 RC Infilling 73
4.6.1 Application 73
4.6.2 Advantages and Disadvantages 73
4.7 Steel Bracing 74
4.7.1 Application 74
4.7.2 Advantages and Disadvantages 77
4.7.3 Design Issues: Modelling Analysis and Checks 78
4.8 Fibre-Reinforced Polymers (FRPs) 78
4.8.1 FRP Composite Materials 78
4.8.2 FRP composites in Civil Engineering and Retrofit 79
4.8.3 FRP Composite Materials 81
4.8.4 FRP Wrapping 82
4.8.5 FRP Laminates 85
4.8.6 Near Surface Mounted FRP Reinforcement 86
4.8.7 FRP Strings 87
4.8.8 Sprayed-FRP 88
4.8.9 Anchoring Issues 89
4.8.10 Advantages and Disadvantages of FRP systems 90
4.8.11 Design Issues 91
4.9 Steel Plates and Steel Jackets 92
4.9.1 Advantages and Disadvantages 94
4.9.2 Design Issues 95
4.10 Damping Devices 95
4.11 Seismic Isolation 96
4.11.1 Type of Base Isolation Systems 99
4.11.2 Advantages and Disadvantages 100
4.11.3 Design Issues 101
4.12 Selective Strengthening and Weakening through Infills 101
4.13 Strengthening of Infills 103
4.13.1 Glass or Carbon FRPs 103
4.13.2 Textile Reinforced Mortars TRM 104
4.13.3 Shotcrete 105
4.14 Connecting New and Existing Members 106
4.14.1 Design issues 107
4.15 Strengthening of individual members 108
4.15.1 Strengthening of RC Columns or Walls 108
4.15.2 Strengthening of RC Beams 109
4.15.3 Strengthening of RC Slabs 111
4.15.4 Strengthening of RC Ground Slabs 111
4.16 Crack Repair - epoxy injections 112
4.17 Protection against corrosion, repair mortars and cathodic protection 113
4.18 Foundation Strengthening 114
4.19 Concluding Remarks Regarding Strengthening Techniques 116
4.20 Evaluation of Different Seismic Retrofitting Solutions: A Case Study 116
4.20.1 Building Configuration 116
4.20.2 Effects of the Infills on the Structural Behaviour 119
4.20.3 Strengthening with Jacketing 121
4.20.4 Strengthening with new RC Walls (entire building height) 122
4.20.5 Strengthening with new RC Walls (ground level only) 124
4.20.6 Strengthening with Braces 126
4.20.7 Strengthening with FRP Wrapping 127
4.20.8 Strengthening with Seismic Isolation 128
4.20.9 Comparison of the Methods 129
4.21 References 130
Chapter 5 Criteria for Selecting Strengthening Methods – Case Studies 156
5.1 Things are Rarely Simple.... 156
5.2 Criteria for Selecting Strengthening Method 157
5.3 Basic Principles of Conceptual Design 159
5.4 Some rules of thumb 161
5.5 Case Studies 164
5.5.1 Case Study1: Seismic upgrade of a 5-storey hotel 164
5.5.2 Case Study2: Seismic upgrade of a 4-storey hotel 166
5.5.3 Case Study 3: Seismic upgrade of a 4-storey hotel 167
5.5.4 Case Study 4: Seismic upgrade of a 3-storey residential building 168
5.5.5 Case Study 5: Seismic upgrade of a 3-storey residential building for the addition of two new floors 168
5.5.6 Case Study 6: Seismic strengthening of an 11-storey building 170
5.5.7 Case Study 7: Seismic strengthening of a 5-storey building 170
5.5.8 Case Study 8: Seismic strengthening of a 3-storey building 171
5.5.9 Case Study 9: Strengthening a building damaged by a severe earthquake 171
5.5.10 Case Study 10: Strengthening of an 11-storey building 172
5.5.11 Case Study 11: Strengthening of a two storey building with basement 173
5.5.12 Case Study 12: Strengthening of a weak ground storey with FRP wraps 174
5.5.13 Case Study 13 (several examples): Strengthening of RC slabs 175
5.5.14 Case Study 14: Strengthening of a ground slab 176
5.5.15 Case Study 15: Strengthening of beam that has failed in shear 176
5.5.16 Case Study 16: Demolition and reconstruction of a RC beam 177
5.5.17 Bonus Case Study 1: Strengthening of an industrial building 177
5.5.18 Bonus Case Study 2: Strengthening of an industrial building 177
5.5.19 Bonus Case Study 3: Strengthening of a residential building 178
5.6 References 178
Chapter 6 Performance Levels & Performance Objectives 179
6.1 Introduction 179
6.1.1 Selection of Performance Objectives in the Design of New Buildings 179
6.1.2 Selection of Performance Objectives in the Assessment of Existing Buildings 180
6.2 Seismic Assessment and Retrofit Procedures 180
6.2.1 Seismic Assessment Procedures 180
6.2.2 Seismic Retrofit Procedures 181
6.3 Understanding Performance Objectives 182
6.3.1 Target Building Performance Levels 182
6.3.2 Seismic Hazard Levels 187
6.3.3 Performance Objectives 188
6.3.4 Eurocode 8, Part-3 and other Standards 189
6.3.5 The Rationale for Accepting a Lower Performance Level for Existing Buildings 191
6.4 Choosing the correct Performance Objective 192
6.5 References 194
Chapter 7 Linear and Nonlinear Methods of Analysis 195
7.1 Introduction 195
7.2 General Requirements 197
7.2.1 Loading Combinations 197
7.2.2 Multidirectional Seismic Effects 198
7.2.3 Accidental torsional effects 198
7.3 Linear Static Procedure 199
7.4 Linear Dynamic Procedure 199
7.5 Nonlinear Structural Analysis 201
7.5.1 Nonlinear Structural Analysis in Engineering Practice 201
7.5.2 Challenges Associated with Nonlinear Analysis 204
7.5.3 Some Theoretical Background 204
7.5.4 Implications from the Basic Assumptions of Nonlinear Analysis 210
7.5.5 How Reliable are Numerical Predictions from Nonlinear Analysis Methods? 212
7.5.6 Closing Remarks 213
7.6 Nonlinear Static Procedure 213
7.6.1 Pushover Analysis 213
7.6.2 Information Obtained with Pushover Analysis 214
7.6.3 Theoretical Background on Pushover Analysis 215
7.6.4 Target Displacement 216
7.6.5 Applying Forces vs. Applying Displacements 217
7.6.6 Controlling the Forces or the Displacements 218
7.6.7 Control Node 219
7.6.8 Lateral Load Patterns 220
7.6.9 Pushover Analysis Limitations 220
7.7 Nonlinear Dynamic Procedure 221
7.7.1 Information Obtained with Nonlinear Dynamic Analysis 223
7.7.2 Selecting and Scaling Accelerograms 223
7.7.3 Advantages and Disadvantages of Nonlinear Dynamic Analysis 226
7.8 Comparative Assessment of Analytical Methods 227
7.8.1 Advantages and Disadvantages of the Analytical Methods 227
7.8.2 Selection of the Best Analysis Procedure for Structural Assessment 228
7.9 References 230
Chapter 8 Structural Modelling in Linear and Nonlinear Analysis 233
8.1 Introduction 233
8.2 Mathematical Modelling 233
8.3 Modelling of Beams and Columns 234
8.3.1 Material Inelasticity 234
8.3.2 Geometric Nonlinearities 235
8.3.3 Modelling of Structural Frame Elements 236
8.4 Modelling of Shear Walls 244
8.5 Modelling of Slabs 244
8.6 Modelling of Stairs 246
8.7 Modelling of Infills 247
8.7.1 A simple Example: infilled frame vs. bare frame 248
8.7.2 Another Example: partially infilled frame (soft storey) vs. bare frame 249
8.7.3 Problems in the Modelling of Infills 250
8.8 Modelling of Beam-Column Joints 251
8.9 Modelling of Bar Slippage 252
8.10 Shear Deformations 252
8.11 Foundation Modelling 253
8.12 How Significant are our Modelling Decisions? 253
8.13 References 254
Chapter 9 Checks and Acceptance Criteria 256
9.1 Introduction 256
9.2 Primary and Secondary Members 257
9.3 Deformation-Controlled & Force-Controlled Actions 258
9.4 Expected vs. Lower-Bound Material Strengths 260
9.5 Knowledge Level & Knowledge Factor 261
9.6 Capacity Checks 261
9.6.1 Capacity Checks for Linear Methods – ASCE 41 262
9.6.2 Capacity Checks for Nonlinear Methods – ASCE 41 264
9.6.3 Capacity Checks for Linear Methods – Eurocode 8, Part-3 265
9.6.4 Capacity Checks for Nonlinear Methods – Eurocode 8, Part-3 266
9.7 Main Checks to be Carried out in an Assessment Procedure 266
9.7.1 Bending Checks 266
9.7.2 Shear Checks 268
9.7.3 Beam-Column Joints 269
9.8 References 270
Chapter 10 Practical Example: Assessment and Strengthening of a 6-storey RC Building 271
10.1 Introduction 271
10.2 Building Description 271
10.3 Knowledge of the Building and Confidence Factor 272
10.3.1 Geometry 272
10.3.2 Reinforcement 272
10.3.3 Material Strengths 273
10.4 Seismic Action and Load Combinations 274
10.5 Structural Modelling 276
10.6 Eigenvalue analysis 277
10.7 Nonlinear Static Procedure 278
10.7.1 Lateral Load Patterns 278
10.7.2 Selection of the Control Node 279
10.7.3 Capacity Curve and Target Displacement Calculation 279
10.7.4 Safety Verifications 282
10.7.5 Chord rotation checks 282
10.7.6 Example of the calculation of Chord rotation capacity 283
10.7.7 Shear Checks 284
10.7.8 Example of the Calculation of Shear Capacity 285
10.7.9 Beam-column Joint Checks 286
10.7.10 Example of the Checks for beam-column Joints 286
10.8 Strengthening of the Building 288
10.8.1 Strengthening with Jackets 288
10.8.2 Designing the Interventions 289
10.8.3 Deliverables 290
10.8.4 Strengthening with Shear Walls 291
10.9 References 292
Appendix A Standards and Guidelines 294
A.1 EUROCODES 294
A.1.1 Performance Requirements 294
A.1.2 Information for Structural Assessment 295
A.1.3 Safety Factors 297
A.1.4 Capacity Models for Assessment and Checks 297
A.1.5 Target Displacement Calculation in Pushover Analysis 301
A.2 ASCE 41-17 304
A.2.1 Performance Requirements 304
A.2.2 Information for Structural Assessment 305
A.2.3 Safety Factors 306
A.2.4 Capacity Models for Assessment and Checks 307
A.2.5 Target Displacement Calculation in the Nonlinear Static Procedure 309
A.3 References 311
Appendix B Poor Construction & Design Practices in Older Buildings 313
B.1 Stirrup Spacing 313
B.2 Lap Splices 313
B.3 Member Alignment 313
B.4 Pipes inside RC Members 313
B.5 Bad Casting of Concrete 313
B.6 Footings 314
Appendix C Methods of Strengthening 315
C.1 Reinforced Concrete Jackets 315
C.2 New Shear Walls 315
C.3 Fibre-reinforced Polymers 315
C.3.1 FRP Wrapping of Columns 315
C.3.2 FRP Wraps in Slabs 315
C.3.3 FRP Wraps for Shear Strengthening 315
C.3.4 FRP Laminates 315
C.3.5 FRP Strings 315
C.4 Steel Braces 315
C.5 Steel Jackets 315
C.6 Steel Plates 316
C.7 Infills 316
C.8 Foundations 316
C.9 Dowels and Anchorages 316
C.10 Demolition with Concrete Cutting 316
C.11 Reinforcement Couplers 316
C.12 Epoxy Injections 316
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