Earthquake risk reduction

Preface xiii 1 Earthquake risk reduction 1 1.1 Introduction 1 1.2 Earthquake risk and hazard 1 1.3 The social and economic consequences of earthquakes 3 1.3.1 Earthquake consequences and their acceptability 3 1.3.2 Economic consequences of earthquakes 7 1.4 Earthquake risk reduction actions 10 2 The nature of earthquakes 15 2.1 Introduction 15 2.2 Global seismotectonics 16 2.3 The strength of earthquakes—magnitude and intensity 20 3 Determination of site characteristics 27 3.1 Introduction 27 3.2 Local geology and soil conditions 27 3.3 Ground classes and microzones 31 3.4 Site investigations and soil tests 34 3.4.1 Introduction 34 3.4.2 Field determination and tests of soil characteristics 35 3.4.3 Laboratory tests relating to dynamic behaviour of soils 40 4 Seismic hazard assessment 45 4.1 Introduction 45 4.2 Crustal strain and moment release 45 4.3 Regional seismotectonics 47 4.4 Faulting 50 4.4.1 Location of active faults 50 4.4.2 Types of fault 51 4.4.3 Degree of fault activity 51 4.4.4 Faults and earthquake magnitudes 56 4.5 Earthquake distribution in space, size and time 61 4.5.1 Introduction 61 4.5.2 Spatial distribution of earthquakes—maps 62 4.5.3 Earthquake distribution in time and size 65 4.5.4 Models of the earthquake process 68 viii Contents 4.6 The nature and attenuation of ground motions 72 4.6.1 Earthquake source models 72 4.6.2 The characteristics of strong ground motion 74 4.6.3 Spatial patterns of ground motions 82 4.6.4 Attenuation of ground motions and spectral response 91 4.6.5 Attenuation of displacement 96 4.6.6 Other conditions that influence ground motions 96 4.7 Design earthquakes 100 4.7.1 Introduction 100 4.7.2 Defining design events 102 4.7.3 Sources of accelerograms and response spectra 105 4.7.4 Response spectra as design earthquakes 106 4.7.5 Accelerograms as design earthquakes 109 4.8 Faults—hazard and design considerations 111 4.8.1 Introduction 111 4.8.2 Probability of occurrence of fault displacements 111 4.8.3 Designing for fault movements 112 4.9 Probabilistic seismic hazard assessment (PSHA) 113 4.10 Probabilistic vs. deterministic seismic hazard assessment 116 5 Seismic response of soils and structures 123 5.1 Introduction 123 5.2 Seismic response of soils 123 5.2.1 Dynamic properties of soils 123 5.2.2 Site response to earthquakes 131 5.3 Seismic response of soil-structure systems 142 5.3.1 Introduction 142 5.3.2 Dynamic analysis of soil-structure systems 144 5.3.3 Soil models for dynamic analysis 145 5.3.4 Useful results from soil-structure interaction studies 157 5.4 Seismic response of structures 162 5.4.1 Elastic seismic response of structures 162 5.4.2 Non-linear seismic response of structures 166 5.4.3 Mathematical models of non-linear seismic behaviour 169 5.4.4 Level of damping in different structures 172 5.4.5 Periods of vibration of structures 173 5.4.6 Interaction of frames and infill panels 174 5.4.7 Methods of seismic analysis for structures 177 6 Earthquake vulnerability of the built environment 189 6.1 Introduction 189 6.2 Qualitative measures of vulnerability 189 6.3 Quantitative measures of vulnerability 191 6.3.1 Introduction 191 6.3.2 Vulnerability of different classes of buildings 198 6.3.3 Vulnerability of contents of buildings 202 Contents ix 6.3.4 Damage models as functions of ground motion measures 208 6.3.5 Microzoning effects on vulnerability functions 209 6.3.6 Upper and lower bounds on vulnerability 220 6.3.7 Earthquake risk reduction potential 221 6.3.8 Human vulnerability to casualties 222 6.3.9 Inter-earthquake effects 224 7 Earthquake risk modelling and management 227 7.1 Earthquake risk modelling 227 7.2 Material damage costs 227 7.2.1 Damage costs directly due to ground shaking using empirical damage ratios 228 7.2.2 Damage costs due to earthquake-induced fires 229 7.2.3 Damage cost estimation using structural response parameters 230 7.3 Estimating casualties 231 7.4 Business interruption 235 7.5 Reduction of business interruption 237 7.6 Planning for earthquakes 239 7.7 Earthquake insurance 242 7.8 Earthquake risk management in developing countries 242 7.9 Impediments to earthquake risk reduction 244 7.10 Further reading 245 8 The design and construction process—choice of form and materials 247 8.1 The design and construction process—performance-based seismic design 247 8.2 Criteria for earthquake resistant design 249 8.2.1 Function, cost and reliability 249 8.2.2 Criteria for reliability of performance 249 8.3 Principles of reliable seismic behaviour—form, material and failure modes 253 8.3.1 Introduction 253 8.3.2 Simplicity and symmetry 254 8.3.3 Length in plan 255 8.3.4 Shape in elevation 256 8.3.5 Uniform and continuous distribution of strength and stiffness 257 8.3.6 Appropriate stiffness 258 8.3.7 Choice of construction materials 261 8.3.8 Failure mode control 262 8.4 Specific structural forms for earthquake resistance 267 8.4.1 Moment-resisting frames 267 8.4.2 Framed tube structures 268 8.4.3 Structural walls (shear walls) 268 8.4.4 Concentrically braced frames 268 8.4.5 Eccentrically braced frames 269 8.4.6 Hybrid structural systems 270 x Contents 8.5 Passive control of structures—energy isolating and dissipating devices 270 8.5.1 Introduction 270 8.5.2 Isolation from seismic motion 271 8.5.3 Seismic isolation using flexible bearings 273 8.5.4 Isolation using flexible piles and energy dissipators 275 8.5.5 Rocking structures 279 8.5.6 Energy dissipators for seismically-isolated structures 281 8.5.7 Energy dissipators for non-isolated structures 281 8.6 Construction and the enforcement of standards 282 8.7 Developing countries 284 9 Seismic design of foundations and soil-retaining structures 287 9.1 Foundations 287 9.1.1 Introduction 287 9.1.2 Shallow foundations 288 9.1.3 Deep box foundations 289 9.1.4 Caissons 290 9.1.5 Piled foundations 290 9.1.6 Foundations in liquefiable ground 301 9.2 Soil-retaining structures 304 9.2.1 Introduction 304 9.2.2 Seismic soil pressures 305 10 Design and detailing of new structures for earthquake ground shaking 313 10.1 Introduction 313 10.1.1 Strength-based vs. displacement-based design 314 10.2 Steel structures 318 10.2.1 Introduction 318 10.2.2 Seismic response of steel structures 319 10.2.3 Reliable seismic behaviour or steel structures 320 10.2.4 Steel beams 323 10.2.5 Steel columns 326 10.2.6 Steel frames with diagonal braces 332 10.2.7 Steel connections 337 10.2.8 Composite construction 342 10.2.9 Further reading 343 10.3 Concrete structures 343 10.3.1 Introduction 343 10.3.2 Seismic response of reinforced concrete 344 10.3.3 Reliable seismic behaviour of concrete structures 344 10.3.4 Reinforced concrete structural walls 355 10.3.5 In situ concrete design and detailing—general requirements 365 10.3.6 Foundations 369 10.3.7 Walls 370 10.3.8 Columns 370 Contents xi 10.3.9 Beams 374 10.3.10 Beam-column joints in moment-resisting frames 375 10.3.11 Structural precast concrete detail 377 10.3.12 Precast concrete cladding detail 385 10.3.13 Prestressed concrete design and detail 388 10.4 Masonry structures 394 10.4.1 Introduction 394 10.4.2 Seismic response of masonry 395 10.4.3 Reliable seismic behaviour of masonry structures 397 10.4.4 Design and construction details for reinforced masonry 398 10.4.5 Construction details for structural infill walls 402 10.4.6 URM in low seismic hazard regions 405 10.5 Timber structures 405 10.5.1 Introduction 405 10.5.2 Seismic response of timber structures 407 10.5.3 Reliable seismic behaviour of timber structures 410 10.5.4 Foundations of timber structures 412 10.5.5 Timber-sheathed walls (shear walls) 413 10.5.6 Timber horizontal diaphragms 415 10.5.7 Timber moment-resisting frames and braced frames 417 10.5.8 Connections in timber construction 420 10.5.9 Fire resistance of timber construction 420 11 Earthquake resistance of services, equipment and plant 429 11.1 Seismic response and design criteria 429 11.1.1 Introduction 429 11.1.2 Earthquake motion—accelerograms 430 11.1.3 Design earthquakes 430 11.1.4 The response spectrum design method 430 11.1.5 Comparison of design requirements for buildings and equipment 432 11.1.6 Equipment mounted in buildings 433 11.1.7 Material behaviour 433 11.1.8 Cost of providing earthquake resistance of equipment 434 11.2 Seismic analysis and design procedures for equipment 434 11.2.1 Design procedures using dynamic analysis 435 11.2.2 Design procedures using equivalent-static analysis 436 11.3 Seismic protection of equipment 443 11.3.1 Introduction 443 11.3.2 Rigidly mounted equipment 444 11.3.3 Equipment mounted on isolating or energy-absorbing devices 445 11.3.4 Light fittings 448 11.3.5 Ductwork 449 11.3.6 Pipework 449 12 Architectural detailing for earthquake resistance 457 12.1 Introduction 457 xii Contents 12.2 Non-structural infill panels and partitions 458 12.2.1 Introduction 458 12.2.2 Integrating infill panels with the structure 459 12.2.3 Separating infill panels from the structure 459 12.2.4 Separating infill panels from intersecting services 461 12.3 Cladding, wall finishes, windows and doors 461 12.3.1 Introduction 461 12.3.2 Cladding and curtain walls 462 12.3.3 Weather seals 462 12.3.4 Wall finishes 462 12.3.5 Windows 463 12.3.6 Doors 463 12.4 Miscellaneous architectural details 464 12.4.1 Exit requirements 464 12.4.2 Suspended ceilings 464 13 Retrofitting 467 13.1 Introduction 467 13.2 To retrofit or not? 468 13.3 Cost-benefit of retrofitting 474 13.4 Retrofitting lifelines 475 13.5 Retrofitting structures 477 13.6 Retrofitting equipment and plant 482 13.7 Performance of retrofitted property in earthquakes 484 13.7.1 Introduction 484 13.7.2 Earthquake performance of retrofitted URM buildings 484 13.7.3 Earthquake performance of retrofitted reinforced concrete buildings 485 Appendix A Modified Mercalli intensity scale (NZ 1996) 489 Appendix B Structural steel standards for earthquake resistant structures 495 Index 497