Fire Safety Engineering Design of Structures
Fire Safety Engineering Design of Structures
Contents
Chapter 1: Fire safety engineering 1
1.1 Design concerns 2
1.1.1 Control of ignition 3
1.1.1.1 Control of flammability 3
1.1.1.2 Control of growth of fire 3
1.1.1.3 Fire safety management 4
1.1.2 Means of escape 4
1.1.3 Detection and control of the fire 6
1.1.3.1 Fire detection 6
1.1.3.2 Smoke control 7
1.1.3.3 Fire-fighting systems 8
1.1.4 Compartmentation 9
1.1.5 Fire spread between structures 10
1.1.6 Structure collapse 10
1.2 Regulatory control 11
1.3 Fire precautions during construction and maintenance 11
1.4 Summary 12
1.4.1 Active measures 13
1.4.2 Passive measures 13
Chapter 2: Design philosophies 14
2.1 Ambient limit state design 14
2.2 Fire limit states 16
2.2.1 Load-bearing capacity criterion 17
2.2.2 Insulation criterion 18
2.2.3 Determination of partial safety factors 18vi Contents
2.3 Assessment models 20
2.3.1 Assessment method – level 1 20
2.3.2 Assessment method – level 2 21
2.3.3 Assessment method – level 3 21
2.3.4 Practical considerations 21
2.4 Applicability of assessment levels 22
2.5 Interaction between active and passive measures 24
Chapter 3: Prescriptive approach 26
3.1 Standard fire test 26
3.2 Drawbacks to the fire test 32
3.2.1 Expense 32
3.2.2 Specimen limitations 33
3.2.3 Effect of restraint or continuity 33
3.2.4 Confidentiality of results 35
3.2.5 Loading 35
3.2.6 Failure modes 35
3.2.7 Reproducibility 36
3.3 Prescriptive determination of fire resistance 37
3.3.1 Concrete 39
3.3.2 Structural steelwork 40
3.3.3 Masonry 41
3.3.4 Timber 41
Chapter 4: Behaviour of natural fires 43
4.1 Development of compartment fires 43
4.1.1 Pre-flashover period 43
4.1.2 Post-flashover period 44
4.1.3 Decay phase 45
4.2 Factors affecting the growth phase 45
4.3 Calculation of compartment temperature–time responses 46
4.3.1 Basic formulation 46
4.3.1.1 Rate of heat release ( ˙ hC) 47
4.3.1.2 Rate of heat loss by radiation through
the openings ( ˙ hR) 48
4.3.1.3 Rate of heat loss due to convection ( ˙ hL) 48
4.3.1.4 Rate of heat loss through the
compartment walls ( ˙ hW) 48
4.3.1.5 Compartment temperature–time
characteristics 48Contents vii
4.3.2 Modifications to allow for other compartment
configurations 50
4.3.2.1 Multiple vertical openings 50
4.3.2.2 Horizontal openings 50
4.3.2.3 Compartment construction 51
4.3.3 Calculation of fire load 51
4.3.3.1 Full calculation 52
4.3.3.2 Generic data 53
4.3.4 Parametric equation approach 53
4.3.4.1 Formulation due to Lie (1974) 54
4.3.4.2 EN 1991-1-2 approach 55
4.4 Estimation of fire characteristics 57
4.5 Fire severity and time equivalence 61
4.5.1 Fire severity 61
4.5.2 Time equivalence 62
4.5.2.1 Temperature base 62
4.5.2.2 Normalized heat load base 65
4.6 Localized fires 77
4.6.1 Plume fires 77
4.6.2 5 MW design fire 77
Chapter 5: Properties of materials at elevated temperatures 78
5.1 Thermal data 78
5.1.1 Steel 79
5.1.1.1 Density 79
5.1.1.2 Specific heat 79
5.1.1.3 Thermal conductivity 80
5.1.1.4 Thermal diffusivity 81
5.1.2 Concrete 81
5.1.2.1 Density 82
5.1.2.2 Specific heat 82
5.1.2.3 Thermal conductivity 84
5.1.2.4 Thermal diffusivity 86
5.1.3 Masonry 86
5.1.3.1 Density 87
5.1.3.2 Specific heat 87
5.1.3.3 Thermal conductivity 87
5.1.4 Timber 88
5.1.5 Aluminium 89
5.1.5.1 Density 89
5.1.5.2 Specific heat 89
5.1.5.3 Thermal conductivity 89viii Contents
5.2 Materials data 90
5.2.1 Testing régimes 90
5.2.2 Steel 92
5.2.2.1 Strength characteristics 92
5.2.2.2 Unrestrained thermal expansion 93
5.2.2.3 Isothermal creep 96
5.2.2.4 Anisothermal creep data 96
5.2.3 Concrete 98
5.2.3.1 Stress–strain data 98
5.2.3.2 Creep 101
5.2.3.3 Free thermal expansion 102
5.2.3.4 Transient tests 104
5.2.3.5 Tensile strength of concrete at elevated
temperature 106
5.2.3.6 Bond strength 106
5.2.3.7 High-strength (HSC) and self-compacting
(SCC) concretes 106
5.2.3.8 Fibre concretes 110
5.2.3.9 Multi-axial behaviour 113
5.2.4 Timber 113
5.2.4.1 Rate of charring 114
5.2.4.2 Strength and elasticity loss 115
5.2.5 Masonry 117
5.2.6 Aluminium 117
5.2.6.1 Strength data 117
5.2.6.2 Thermal expansion 119
5.3 Constitutive stress–strain laws 119
5.3.1 Steel 121
5.3.1.1 Elastic strain 121
5.3.1.2 Creep 124
5.3.1.3 Design curves 127
5.3.2 Concrete 129
5.3.2.1 Anderberg and Thelandersson 132
5.3.2.2 Diederichs 134
5.3.2.3 Khoury and Terro 135
5.3.2.4 Khennane and Baker 136
5.3.2.5 Schneider 138
5.3.2.6 Li and Purkiss 140
5.3.3 Design code provisions for stress–strain behaviour 140
Chapter 6: Calculation approach 142
6.1 Thermal analysis 143
6.1.1 Governing equation and boundary conditions 143
6.1.2 Finite element solution of the heat transfer problem
6.2 Calculation of temperature in timber element 154
6.3 Structural analysis 154
6.3.1 Calculation of structural responses using
simple approaches 155
6.3.2 Calculation of structural responses using
finite element analysis packages 158
6.4 Examples 161
Chapter 7: Design of concrete elements 168
7.1 Calculation of temperatures 169
7.1.1 Graphical data 169
7.1.1.1 The ISE and Concrete Society design
guide (1978) 169
7.1.1.2 FIP/CEB report (1978) 169
7.1.1.3 EN 1992-1-2 169
7.1.2 Empirical methods 170
7.1.2.1 Wickström’s method 170
7.1.2.2 Hertz’s method 171
7.1.3 Values of thermal diffusivity 173
7.1.4 Position of the 500◦C isotherm 174
7.2 Simple calculation methods 175
7.2.1 Calculation of load effects 175
7.2.1.1 Direct calculation 175
7.2.1.2 Indirect calculation 175
7.2.2 Materials’ partial safety factors 176
7.2.3 Methods of determining section capacity 176
7.2.3.1 Reduced section method (500◦C isotherm) 176
7.2.3.2 Method of slices (zone method) 180
7.3 Columns 191
7.4 Comparisons between the methods of calculation 196
7.5 Design and detailing considerations 197
7.5.1 Shear 197
7.5.2 Bond 197
7.5.3 Spalling 198
7.5.3.1 Moisture content 198
7.5.3.2 Concrete porosity and permeability 198
7.5.3.3 Stress conditions 199
7.5.3.4 Aggregate type 200
7.5.3.5 Section profile and cover 200
7.5.3.6 Heating rate 200
7.5.3.7 Concrete strength 201
7.5.4 High strength concrete and self-compacting concrete 201
7.5.5 Detailing 201x Contents
Chapter 8: Design of steel elements 203
8.1 Calculation of temperatures 203
8.1.1 Basic principles 203
8.1.2 Heat flow in uninsulated steelwork 205
8.1.3 Heat flow in insulated steelwork 206
8.1.3.1 ECCS method of calculation 206
8.1.3.2 EN 1993-1-2 approach 207
8.1.4 Effect of moisture 208
8.1.4.1 Effective density of insulation 208
8.1.4.2 Delay time 208
8.1.5 Empirical approach for the calculation of
temperatures 209
8.1.5.1 Bare steelwork 209
8.1.5.2 Protected steelwork 209
8.1.6 Calculation of Am/V 210
8.1.7 Thermal properties of insulation materials 210
8.2 Design of non-composite steelwork 220
8.2.1 Determination of structural load in the fire limit state 220
8.2.2 EN 1993-1-2 approach for the determination
of structural fire capacity 220
8.2.2.1 Background to the EuroCode method 220
8.2.2.2 EuroCode methods 222
8.3 Other steelwork constructions 241
8.3.1 External steelwork 241
8.3.2 Shelf angle floors 241
8.4 Stainless steel 247
8.5 Methods of protection 247
8.5.1 Types of protection 247
8.5.1.1 Board systems 247
8.5.1.2 Spray protection 248
8.5.1.3 Intumescent paints 248
8.5.1.4 Brickwork/blockwork 248
8.5.1.5 Concrete encasement 248
8.5.1.6 Manufacturer’s data 249
8.5.2 Connections 250
8.5.3 Ageing of and partial loss of protection 251
8.5.3.1 Ageing effects 251
8.5.3.2 Partial loss of protection 252
Chapter 9: Composite construction 253
9.1 Composite slabs 253
9.1.1 Insulation requirement 253
9.1.1.1 Calculation approach 254
9.1.1.2 Effective thickness 254Contents xi
9.1.2 Load-bearing capacity 255
9.1.2.1 Calculation of moment capacity 256
9.2 Composite beams 266
9.2.1 Critical temperature approach 267
9.2.2 Full moment calculation 267
9.3 Composite steel and concrete columns 275
9.3.1 Concrete filled rolled hollow steel columns 275
9.3.1.1 EN 1994-1-2 275
9.3.1.2 Empirical methods 276
9.3.2 Web-infilled columns 277
Chapter 10: Design of timber elements 278
10.1 Design to EN 1995-1-2 278
10.1.1 Depth of charring 278
10.1.1.1 Exposure to the standard furnace curve 278
10.1.1.2 Charring to parametric exposure
(Annex A) 279
10.1.2 Calculation of structural capacity 281
10.1.2.1 Effective section method 281
10.1.2.2 Reduced strength and stiffness method 281
10.2 Empirical approaches 286
10.2.1 Approach developed by Ödeen 286
10.2.2 Approach developed by Lie for beams 288
10.2.3 Empirical determination of fire endurance
for columns 289
10.2.4 Approach developed by Stiller 291
10.2.4.1 Beams 292
10.2.4.2 Columns 292
10.3 Timber floors and protected timber systems 294
10.3.1 Timber floors 294
10.3.2 Protected timber systems 294
Chapter 11: Masonry, aluminium, plastics and glass 297
11.1 Masonry 297
11.1.1 Insulation requirements of masonry
construction 297
11.1.2 Thermal bowing 298
11.1.3 Load-bearing cavity walls 299
11.2 Aluminium 300
11.3 Plastics and plastic-based composites 301
11.4 Glass 302xii Contents
Chapter 12: Frames 303
12.1 Tests on isolated frames and connections 303
12.1.1 Frame tests 303
12.1.2 Fire tests on beam and column assemblies 304
12.2 Tests on the large frame structures at Cardington 305
12.2.1 Timber frame structure 305
12.2.2 Concrete frame structures 306
12.2.3 Composite steel frames 308
12.3 Pitched roof portals 316
Chapter 13: Assessment and repair of fire-damaged structures 323
13.1 Visual inspection 323
13.1.1 Stability 323
13.1.2 Estimation of fire severity 324
13.2 Damage assessment 326
13.2.1 Structural survey 326
13.2.2 Materials testing 327
13.2.2.1 Concrete 327
13.2.2.2 Steel 335
13.3 Strength assessment of the structure 335
13.3.1 Residual properties 336
13.3.1.1 Concrete 336
13.3.1.2 Structural steel 339
13.3.1.3 Reinforcing and pre-stressing steels 340
13.3.1.4 Cast and wrought iron 340
13.3.1.5 Masonry 341
13.3.2 Determination of temperatures within an element 341
13.4 Methods of repair 343
13.5 Demolition of fire-damaged structures 345
Chapter 14: Postscript 347
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