Designing steel structures for fire safety 2009

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1. Designing Steel Structures for Fire Safety 2. Designing Steel Structures for Fire Safety Jean-Marc Franssen Department of Architecture, Geology, Environment &…
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  • 1. Designing Steel Structures for Fire Safety
  • 2. Designing Steel Structures for Fire Safety Jean-Marc Franssen Department of Architecture, Geology, Environment & Constructions, University of Liège, Liege, Belgium Venkatesh Kodur Department of Civil & Environmental Engineering, Michigan State University, East Lansing, USA Raul Zaharia Department of Steel Structures and Structural Mechanics, “Politehnica’’ University of Timisoara,Timisoara, Romania
  • 3. Cover photo: Courtesy of CTICM, GSE and INERIS Taylor & Francis is an imprint of the Taylor & Francis Group, an informa business ©2009 Taylor & Francis Group, London, UK Typeset by Macmillan Publishing Solutions, Chennai, India Printed and bound in Great Britain by TJ International Ltd, Padstow, Cornwall All rights reserved. No part of this publication or the information contained herein may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, by photocopying, recording or otherwise, without written prior permission from the publishers. Although all care is taken to ensure integrity and the quality of this publication and the information herein, no responsibility is assumed by the publishers nor the author for any damage to the property or persons as a result of operation or use of this publication and/or the information contained herein. Published by: CRC Press/Balkema P.O. Box 447, 2300 AK Leiden,The Netherlands e-mail: Pub.NL@taylorandfrancis.com www.crcpress.com – www.taylorandfrancis.co.uk – www.balkema.nl British Library Cataloguing in Publication Data A catalogue record for this book is available from the British Library Library of Congress Cataloging-in-Publication Data Franssen, Jean-Marc. Designing steel structures for fire safety / Jean-Marc Franssen,Venkatesh Kodur, Raul Zaharia. p. cm. Includes bibliographical references. ISBN 978-0-415-54828-1 (hardcover : alk. paper) – ISBN 978-0-203-87549-0 (e-book) 1. Building, Fireproof. 2. Building, Iron and Steel. I. Zaharia, Raul. II. Kodur, Venkatesh. III. Title. TH1088.56.F73 2009 693.8 2–dc22 2009006378 ISBN 978-0-415-54828-1(Hbk) ISBN 978-0-203-87549-0(eBook)
  • 4. Table of Contents Foreword XI Preface XIII Notations XVII Author profiles XXI CHAPTER 1 – INTRODUCTION 1 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 11 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
  • 5. VI Table of Contents 2.3.5 Indirect fire actions 16 2.3.6 Simplified rule 18 CHAPTER 3 –THERMAL ACTION 21 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 39 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 – MECHANICAL ANALYSIS 57 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
  • 6. Table of Contents VII 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 101 6.1 General 101 6.2 Simplified procedure 102 6.3 Detailed analysis 104
  • 7. VIII Table of Contents 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 107 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 125 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 PROPERTIES AND TEMPERATURE PROFILES 139 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 149 II.1 Eurocode properties 149 II.1.1 Strength and deformation properties 149 II.1.2 Thermal elongation 151
  • 8. Table of Contents IX 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
  • 9. Foreword This book is a major new contribution to the wider understanding of structural behaviour in fires. The art and science of designing structures for fire safety has grown dramatically in recent years, accompanied by the development of sophisticated codes of practice such as the Eurocodes. The Eurocode documents have evolved over sev- eral decades and now represent the best international consensus on design rules for structures exposed to fires. Codes alone do not provide enough information for designers, especially as they become more sophisticated and comprehensive. Most codes have been written by a small army of dedicated experts, some of whom have been immersed in the project for many years with the responsibility to provide the correct rules, not always provid- ing adequate guidance for using those rules. Designers want to understand the basic concepts of the code and the philosophy of the code-writers, together with hands-on advice for using the code. Structural design for fire is conceptually similar to structural design for normal temperature conditions, but often more difficult because of internal forces induced by thermal expansion, strength reduction due to elevated temperatures, much larger deflections, and many other factors. Before making any design it is essential to establish clear objectives, and determine the severity of the design fire. This book shows how these factors are taken into account, and gives guidance for all those wishing to use the Eurocodes for fire design of steel structures. Prof. Jean-Marc Franssen has been a pioneer in the field of structural design for fire safety, with extensive involvement in codes, software development, research, teach- ing, and consulting. He is also well known for establishing the SiF Structures in Fire international workshops. His co-authors are Dr Raul Zaharia, a leading European researcher in structural fire engineering, Prof. Venkatesh Kodur from Michigan State University who is one of the top researchers and teachers in structural fire design in North America. Together they have produced a book which will be extremely valuable to any design professionals or students wishing to use and understand Eurocode 3, or to learn more about the design of steel structures exposed to fires. The fire sections of the Eurocodes are considered to be among the most advanced international codes of practice on fire design of structures, and have attracted attention around the world. This book is an excellent introduction for readers from other regions who wish to become knowledgeable about the philosophy, culture and details of the Eurocodes for structural fire design. Professor Andy Buchanan University of Canterbury, New Zealand
  • 10. Preface Fire represents one of the most severe conditions encountered during the life-time of a structure and therefore, the provision of appropriate fire safety measures for structural members is a major safety requirement in building design. The basis for this requirement can be attributed to the fact that when other measures for containing the fire fail, structural integrity is the last line of defence. The historical approach for evaluating fire resistance of structural members is through prescriptive-based methodologies. These methodologies have significant drawbacks and do not provide rational fire designs. Therefore, in the last two decades there has been important research endeavours devoted to developing better under- standing of structural behaviour under fire conditions and also to develop rational design approaches for evaluating fire resistance of structures. This activity was partic- ularly significant in Western Europe where numerous research reports, Ph.D. theses and scientific papers were published. European technical committees were in the fore-front to implement some of the research findings in to codes and standards to enable the application of rational fire engineering principles in the design of structures. Among the first internationally recog- nised codes of practice are, for steel elements, the recommendations of the ECCS “European Convention for Constructional Steelwork’’ (ECCS 1983) and, for concrete elements, the recommendations of the CEB/FIP “Comité Euro-International du béton / Fédération Internationale de la précontrainte’’ (CEB 1991). The fire parts of the Eurocodes were first presented in Luxemburg in 1990. Over the next few years these Eurocode documents have been significantly updated by incorporating new or updated provisions based on latest research findings reported from around the world. On similar lines, in the last few years, many countries have moved towards imple- menting rational fire design methodologies in codes and standards. One such example is the recent introduction of rational fire design approach in the latest edition of Amer- ican Institute of Steel Construction’s steel design manual. In addition, a number of countries around the world are updating their codes and standards by introducing performance-based fire safety design provisions. A performance-based approach to fire safety often facilitates innovative, cost-effective and rational designs. However, under- taking performance-based fire safety design requires the advanced models, calculation methodologies, design manuals books and trained personnel. The Eurocode documents, or recently updated codes and standards in other coun- tries, are nevertheless far from being useful textbooks, lecture notes or guidance documents. While these codes and standards provide specifications for undertaking
  • 11. XIV Preface rational fire design, there is no detailed commentary or explanation for the various specifications or calculation methodologies. Added to this, fire design is rarely taught as part of regular engineering curriculum and thus most engineers, architects and regu- lators may not be fully versed with the necessary background to easily understand the relevant clauses, or to make interpretations, or to recognise the limits of application of various rules. In other words, unless one has some level of expertise in fire safety engi- neering, it is not easy to apply the current provisions in codes and standards in most practical situations. Compounding this problem is the fact that there is only handful number of text books in the area of structural fire engineering. This book is aimed at filling the current gaps in structural fire engineering by pro- viding necessary background information for rational fire design of steel structures. It deals with various calculation methodologies for fire design and analyses structural steel elements, assemblies and systems. The intent is to provide a basis for engineers with traditional backgrounds to evaluate the fire response of steel structures at any level of complexity. Since the main aim of the book is to help facilitate rational fire design of steel structures, the book relies heavily on Eurocode 3 provisions, as well as relevant fire provisions in American and other codes and standards. In this book the information relevant to fire design of steel structures is presented in a systematic way in seven chapters. Each Chapter begins with an introduction of various concepts to be covered and follows with detailed explanation of the concepts. The calculation methods as relevant to code provisions (in Europe, North America or other continents) are discussed in detail. Worked examples relevant to calculation methodologies on simple structural elements are presented. For the case of complete structures guidance on how analysis can be carried out is presented. Chapter 1 of the book is devoted to providing relevant background information to codes and standards and principles of fire resistance design. The chapter discusses the fire safety design philosophies, prescriptive and performance-based design fire safety design issues. Chapter 2 deals with basis of design and mechanical loads. The load combinations to be considered for fire design of structures, as per European and North American codes and standards, are discussed. Chapter 3 discusses the detailed steps involved in establishing the fire scenarios for various cases. Both Eurocode and North American temperature-time relationships are discussed. Procedures in this section allow the designer to establish the time- temperature relationships or heat flux evolutions under a specified design fire. Chapter 4 deals with steps associated in establishing the temperature history in the steel struc- ture, resulting from fire temperature. The various approaches for undertaking thermal analysis by simple calculation models are discussed. Chapter 5 presents the steps associated for establishing the mechanical response of a structure exposed to fire. The possibilities for analysis at different levels: member level, sub-structure level and global level are discussed. Full details related to simple calculation methods for undertaking strength analysis at member level are presented. Chapter 6 is devoted to fire resistance issues associated with design of joints. The steps associated with the fire resistance of a bolted or a welded joint through simplified and detailed procedure are discussed. Chapter 7 deals with thermal and mechanical analysis through advanced calculation models. The procedures involved in the sub-structure analysis or global structural analysis under fire exposure is fully discussed. Case studies are presented to illustrate
  • 12. Preface XV the detailed fire resistance analysis of various structures. Chapter 8 presents four design examples showing how a complex structure can be designed using the concept of element or sub-structure analysis. The book concludes with two Annexes which present some of the design information related to material properties and temperature profiles. Annex 1 focuses on thermal properties of structural steel and commonly used insulation materials and resulting temperature profiles in steel. Annex 2 focuses on mechanical properties of structural steel. This text book is a reference that allows designers to go beyond current prescriptive approaches that generally do not yield a useful understanding of actual performance during a fire, into analyses that give realistic evaluation of structural fire performance. The book is a compendium of essential information for determination of the effects of fire on steel structures. However, the book is not a substitute for the complete text of Eurocode 3 or any other codes and standards. The book should help a reader not familiar with fire safety engineering to make relevant calculations for establishing the fire response of steel structures. The target audience for this book is professionals in engineering or architecture, students or teachers in these disciplines, and building officials and regulators. A good knowledge of mechanics of structures is essential when reading this book, while general background on the design philosophy related to building structures is an advantage. It is hoped that the book will enable researchers, practioners and students to develop greater insight of structural fire engineering, so that safer structures could be designed for fire conditions. If needed, an errata list will be placed on www.structuresinfire.com. Jean-Marc Franssen, Venkatesh Kodur, Raul Zaharia jm.franssen@ulg.ac.be kodur@egr.msu.edu raul.zaharia@ct.upt.ro
  • 13. Notations Latin upper case letters A cros
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