Designing Steel Structures for Fire Safety (KET0058)

Designing Steel Structures for Fire Safety

Table of Contents

CHAPTER 1 – INTRODUCTION

1.1 Fire safety design 1

1.2 Codes and standards 1

1.2.1 General 1

1.2.2 Fire safety codes 2

1.2.3 North American codes and standards 3

1.2.4 European codes: the Eurocodes 4

1.3 Design for fire resistance 5

1.3.1 Fire resistance requirements 5

1.3.2 Fire resistance assessment 6

1.3.3 Eurocodes 6

1.3.4 Scope of Eurocode 3 – Fire part 7

1.4 General layout of this book 9

CHAPTER 2 – MECHANICAL LOADING

2.1 Fundamental principles 11

2.1.1 Eurocodes load provisions 11

2.1.2 American provisions for fire design 14

2.2 Examples 14

2.2.1 Office building 14

2.2.2 Beam for a shopping centre 15

2.2.3 Beam in a roof 15

2.3 Specific considerations 15

2.3.1 Simultaneous occurrence 15

2.3.2 Dead weight 15

2.3.3 Upper floor in an open car park 16

2.3.4 Industrial cranes 16

2.3.5 Indirect fire actions 16

2.3.6 Simplified rule 18

CHAPTER 3 –THERMALACTION

3.1 Fundamental principles 21

3.1.1 Eurocode temperature-time relationships 21

3.1.1.1 Nominal fire curves 21

3.1.1.2 Equivalent time 22

3.1.1.3 Parametric temperature–time curves 23

3.1.1.4 Zone models 25

3.1.1.5 Heat exchange coefficients 26

3.1.2 Eurocode localised fire, flame not impacting the ceiling 26

3.1.3 Eurocode localised fire, flame impacting the ceiling 28

3.1.4 CFD models in the Eurocode 31

3.1.5 North American time–temperature relationships 32

3.2 Specific considerations 33

3.2.1 Heat flux to protected steelwork 33

3.2.2 Combining different models 34

3.3 Examples 35

3.3.1 Localised fire 35

3.3.2 Parametric fire – ventilation controlled 36

3.3.3 Parametric fire – fuel controlled 37

CHAPTER 4 –TEMPERATURE IN STEEL SECTIONS

4.1 General 39

4.2 Unprotected internal steelwork 39

4.2.1 Principles 39

4.2.2 Examples 44

4.2.2.1 Rectangular hollow core section 44

4.2.2.2 I-section exposed to fire on 4 sides and subjected to a nominal fire 44

4.2.2.3 I-section exposed to fire on 3 sides 44

4.3 Internal steelwork insulated by fire protection material 45

4.3.1 Principles 45

4.3.2 Examples 50

4.3.2.1 H section heated on four sides 50

4.3.2.2 H section heated on three sides 50

4.4 Internal steelwork in a void protected by heat screens 51

4.5 External steelwork 52

4.5.1 General principles 52

4.5.2 Example 52

CHAPTER 5 – MECHANICALANALYSIS

5.1 Level of analysis 57

5.1.1 Principles 57

5.1.2 Boundary conditions in a substructure or an element analysis 58

5.1.3 Determining Efi,d,0 59

5.2 Different calculation models 60

5.2.1 General principle 60

5.2.1.1 Tabulated data 60

5.2.1.2 Simple calculation models 61

5.2.1.3 Advanced calculation models 61

5.2.2 Relations between the calculation model and the part of the structure that is analysed 62

5.2.3 Calculation methods in North America 62

5.3 Load, time or temperature domain 63

5.4 Mechanical properties of carbon steel 66

5.5 Classification of cross-sections 67

5.6 How to calculate Rfi,d,t? 70

5.6.1 General principles 70

5.6.2 Tension members 71

5.6.3 Compression members with Class 1, 2 or 3 cross-sections 72

5.6.4 Beams with Class 1, 2 or 3 cross-section 76

5.6.4.1 Resistance in shear 76

5.6.4.2 Resistance in bending 76

5.6.4.2.1 Uniform temperature distribution 76

5.6.4.2.2 Non-uniform temperature distribution 77

5.6.4.3 Resistance to lateral torsional buckling 82

5.6.5 Members with Class 1, 2 or 3 cross-sections, subject to combined bending and axial compression 83

5.6.6 Members with Class 4 cross-sections 87

5.7 Design in the temperature domain 88

5.8 Design examples 90

5.8.1 Member in tension 90

5.8.1.1 Verification in the load domain 90

5.8.1.2 Verification in the time domain 91

5.8.1.3 Verification in the temperature domain 91

5.8.2 Column under axial compression 92

5.8.2.1 Fire resistance time of the column with unprotected cross-section 92

5.8.2.2 Column protected with contour encasement of uniform thickness 94

5.8.3 Fixed-fixed beam supporting a concrete slab 94

5.8.3.1 Classification of the section, see Table 5.2 94

5.8.3.2 Verification in the load domain 95

5.8.3.3 Verification in the time domain 96

5.8.3.4 Verification in the temperature domain 97

5.8.3.5 Beam protected with hollow encasement 97

5.8.4 Class 3 beam in lateral torsional buckling 98

CHAPTER 6 – JOINTS

6.1 General 101

6.2 Simplified procedure 102

6.3 Detailed analysis 104

6.3.1 Temperature of joints in fire 104

6.3.2 Design resistance of bolts and welds in fire 104

6.3.2.1 Bolted joints in shear 104

6.3.2.2 Bolted joints in tension 105

6.3.2.3 Fillet welds 106

6.3.2.4 Butt welds 106

CHAPTER 7 –ADVANCED CALCULATION MODELS

7.1 General 107

7.2 Introduction 108

7.3 Thermal analysis 109

7.3.1 General features 109

7.3.2 Capabilities of the advanced thermal models 109

7.3.3 Limitations of the advanced thermal models 112

7.3.4 Discrepancies with the simple calculation models 113

7.4 Mechanical analysis 114

7.4.1 General features 114

7.4.2 Capabilities of the advanced mechanical models 117

7.4.3 Limitations of the advanced mechanical models 119

7.4.4 Discrepancies with the simple calculation models 123

CHAPTER 8 – DESIGN EXAMPLES

8.1 General 125

8.2 Continuous beam 125

8.3 Multi-storey moment resisting frame 126

8.4 Single storey industrial building 129

8.5 Storage building 133

ANNEX I – HIGHTEMPERATURE PROPERTIESAND TEMPERATURE PROFILES

I.1 Thermal properties of carbon steel 139

I.1.1 Eurocode properties 139

I.1.1.1 Thermal conductivity 139

I.1.1.2 Specific heat 139

1.1.2 Thermal properties of steel according to ASCE 141

I.1.2.1 Thermal conductivity 141

I.1.2.2 Specific heat 141

I.2 Thermal properties of fire protection materials 141

I.3 Temperatures in unprotected steel sections (Eurocode properties) 143

I.4 Temperatures in protected steel sections (Eurocode properties) 146

ANNEX II – MECHANICAL PROPERTIES OF CARBON STEELS

II.1 Eurocode properties 149

II.1.1 Strength and deformation properties 149

II.1.2 Thermal elongation 151

II.2 ASCE properties 152

II.2.1 Stress strain relations for steel (Version 1) 152

II.2.2 Stress strain relations for steel (Version 2 153

II.2.3 Coefficient of thermal expansion 154

Bibliography 155

Subject index 161