Steel and Composite Structures – Behaviour and design for fire safety (KET0059)

Steel and Composite Structures – Behaviour and design for fire safety

Contents

1 Introduction

1.1 Background 1

1.2 Layout 4

1.3 Scope 7

2 An introduction to the behaviour and design at ambient temperature

2.1 Local buckling of steel plates 10

2.2 Steel beams 11

2.2.1 Plastic bending moment capacity 11

2.2.2 Lateral torsional buckling 12

2.2.3 Design calculations according to the British Standard BS 5950 Part 1 14

2.3 Steel columns 16

2.4 Combined axial load and bending 20

2.5 Composite beams 21

2.5.1 Partial shear connection 22

2.6 Composite columns 23

2.7 Plastic design of continuous beams 25

2.8 Semi-rigid design approach 26

3 Experimental observations

3.1 General test procedure 29

3.2 Standard fire resistance tests 29

3.2.1 Test methodology 30

3.2.2 A critical assessment of the standard fire resistance test method 31

3.3 Fire tests on steel columns 33

3.3.1 Cross-section yield 33

3.3.2 Global buckling behaviour 33

3.3.3 Local buckling 36

3.3.4 Summary of fire tests on isolated steel columns 38

3.4 Fire tests on restrained columns 39

3.4.1 Effects of restrained thermal expansion 39

3.4.2 Effects of rotational restraints 42

3.4.3 Summary of fire tests on restrained columns 42

3.5 Fire tests on composite columns 42

3.5.1 Local buckling of steel 42

3.5.2 Global buckling behaviour 43

3.5.3 Restrained composite columns 46

3.5.4 Summary of fire tests on composite columns 47

3.6 Fire tests on steel and composite beams 48

3.6.1 Behaviour of bare steel beams in fire 48

3.6.2 Composite beams 49

3.6.3 Restrained beams 51

3.6.4 Summary of fire tests on beams 52

3.7 Fire tests on slabs 52

3.8 Fire tests on connections 53

3.8.1 SCI tests 54

3.8.2 Collaborative investigations between the University of Sheffield and Building Research Establishment

3.8.3 Behaviour of frame connections in fire 56

3.8.4 Summary of fire tests on connections 56

3.9 Fire tests on skeletal frames 57

3.9.1 Tests of Rubert and Schaumann on 1/4 scale steel frames, Germany 57

3.9.2 Tests of Fire Research Station and Corns on a rugby post frame (Cooke and Latham 1987), UK

3.9.3 Small scale tests on rigid steel frames at Tongji University, China 59

3.9.4 Model steel frame tests, Japan 59

3.9.5 Tests of Kimura et al. on composite column assembly, Japan 60

3.9.6 Parametrical fire testing of full scale structural assemblies, University of Manchester, UK

3.9.7 Summary of fire tests on skeletal frames 66

3.10 Fire tests on complete buildings 66

3.10.1 Behaviour of the Broadgate building in a fire accident 67

3.10.2 Fire tests on an eight-storey steel-framed building in Cardington, UK 68

3.11 Concluding remarks and some suggestions for further experimental studies 82

4 Numerical modelling

4.1 Requirements of a computer program 86

4.2 Modelling structural behaviour in fire on an element level 87

4.2.1 Beams and columns 87

4.2.2 Connections 87

4.2.3 Slab modelling 88

4.3 Modelling structural behaviour in fire on a global level 88

4.4 Other general modelling requirements 89

4.5 A brief review of some existing computer programs 90

4.5.1 ADAPTIC 91

4.5.2 FEAST 94

4.5.3 SAFIR 97

4.5.4 VULCAN 99

4.5.5 Commercial programs (ABAQUS and DIANA) 102

4.6 Simplified frame analysis methods 104

4.7 Summary and some recommendations 105

5 Behaviour of steel and composite structures in fire

5.1 Material properties at elevated temperatures 107

5.1.1 Steel 108

5.1.2 Concrete 113

5.2 Behaviour of unrestrained columns in fire 116

5.2.1 Local buckling 116

5.2.2 Global behaviour 118

5.2.3 Composite columns 122

5.3 Behaviour of restrained columns in fire 124

5.3.1 Effects of axial restraint on column thermal expansion 125

5.3.2 Post-buckling behaviour of an axially restrained column 127

5.3.3 Bending moments in restrained columns in fire 131

5.3.4 Effective length of restrained columns in fire 134

5.4 Summary of column behaviour in fire 138

5.5 Behaviour of beams in fire 139

5.5.1 Statically determinate beams 139

5.5.2 Longitudinally and rotationally restrained beams in fire 146

5.5.3 Catenary action in a restrained beam in fire 149

5.6 Behaviour of slabs in fire 154

5.6.1 Flexural bending behaviour of slabs at small deflections—yield line analysis 154

5.6.2 Membrane action in slabs at large deflections 155

5.6.3 Compressive membrane action 157

5.6.4 Tensile membrane action 157

5.7 Other aspects of frame behaviour in fire 165

5.7.1 Remote areas of building 165

5.7.2 Fire spread 165

5.7.3 Effect of bracing locations 167

5.7.4 Alternative load path 168

5.8 Concluding remarks 168

6 An introduction to heat transfer

6.1 Heat conduction 171

6.1.1 One-dimensional steady-state heat conduction 171

6.1.2 One-dimensional steady-state heat conduction in a composite element 171

6.1.3 Boundary conditions for one-dimensional heat conduction 174

6.2 Connective heat transfer 175

6.2.1 Heat transfer coefficients for forced convection 176

6.2.2 Heat transfer coefficients for natural convection 177

6.2.3 Approximate values of connective heat transfer coefficients for fire safety 178

6.3 Radiant heat transfer 179

6.3.1 Blackbody radiation 179

6.3.2 Radiant heat transfer of grey body surfaces 185

6.4 Some simplified solutions of heat transfer 188

6.4.1 Temperatures of unprotected steelwork in fire 189

6.4.2 Temperatures of protected steelwork in fire 190

6.5 Thermal properties of materials 193

6.5.1 Steel 193

6.5.2 Concrete 195

6.5.3 Insulation materials 196

6.6 Numerical analysis of heat transfer 198

6.6.1 Three-dimensional steady-state heat conduction 198

6.6.2 Three-dimensional transient-state heat conduction 199

6.6.3 Boundary conditions for heat transfer 199

7 An introduction to enclosure fire behaviour 201

7.1 A general description of enclosure fire behaviour and its modelling 201

7.2 Behaviour of localized fires 206

7.2.1 Thomas model of smoke temperature 206

7.2.2 Hasemi’s model 207

7.3 Post-flashover fire modelling 209

7.3.1 Rate of heat release in fire ( fi) 210

7.3.2 Heat loss due to hot gas leaving fire enclosure ( lc) 214

7.3.3 Heat loss to the enclosure wall ( lw) 216

7.3.4 Heat loss to the cold air by radiation through opening ( lr) 217

7.3.5 Heat required to increase the fire temperature ( lg) 218

7.3.6 Some approximate temperature—time relationships for post-flashover fires 218

7.3.7 Fire load and compartment lining properties 222

7.3.8 Standard fires 222

7.3.9 Equivalent fire times 223

7.4 Concluding remarks 226

8 Design of steel structures for fire safety

8.1 Basis of design 228

8.1.1 Scope of design calculations 228

8.1.2 Loading 229

8.1.3 Performance of fire protection materials 229

8.1.4 Fire resistant design according to BS 5950 Part 8 229

8.1.5 Fire resistant design according to Eurocode 3 Part 1.2 230

8.2 Overview of design methods 230

8.2.1 BS 5950 Part 8 230

8.2.2 Eurocode 3 Part 1.2 232

8.3 Fire resistant design of steel beams 233

8.3.1 BS 5950 Part 8 233

8.3.2 Eurocode 3 Part 1.2 method 238

8.3.3 A comparison between Part 8 and EC3 for lateral torsional buckling 242

8.3.4 Modifications to the EC3 method 245

8.3.5 Temperatures in steel beams 246

8.3.6 Summary of fire resistant design calculations for lateral torsional buckling resistance

8.4 Fire resistant design of steel columns 249

8.4.1 Axially loaded columns with uniform temperature distribution 249

8.4.2 Effects of structural continuity 256

8.4.3 Columns with bending moments 258

8.5 Fire resistant design of connections 259

8.6 Fire resistant design of cold-formed thin-walled structures 260

8.6.1 The Steel Construction Institute design guide 261

8.6.2 Temperatures in thin-walled steel structures 263

8.7 Stainless steel structures 264

8.8 Other types of steel structures 264

8.8.1 Portal frames 265

8.8.2 Water cooled structures 266

8.8.3 External steelwork 266

8.9 Cost effective design of steel structures for fire protection 267

8.10 Feasibility of using catenary action to eliminate fire protection in beams 269

8.11 Concluding remarks 271

9 Design of composite structures for fire safety

9.1 Composite slabs 272

9.1.1 Load bearing capacity of one-way spanning composite slabs 273

9.1.2 Sagging bending moment capacity M+, fi 274

9.1.3 Hogging bending moment capacity M- , fi 274

9.1.4 Load bearing capacity of two-way spanning slabs 275

9.2 Composite beams 277

9.2.1 BS 5950 Part 8 277

9.2.2 Eurocode 4 Part 1.2 277

9.3 Composite columns 281

9.3.1 Resistance to axial load according to EC4 281

9.3.2 Simplified calculation methods for concrete filled columns 282

9.3.3 Effect of eccentricity 294

9.3.4 High strength concrete filled columns 294

9.4 Concluding remarks 295

10 Steel and composite structures without fire protection

10.1 Reducing the fire resistance requirement 296

10.2 Increasing the fire resistance of unprotected steel structures 299

10.2.1 Enhancing the fire resistance of individual members 299

10.2.2 Utilizing whole building performance in fire 304

10.3 Concluding remarks 307