Fourth Edition
This edition first published 2019
© 2019 John Wiley & Sons Ltd
Edition History
Crosby Lockwood Staples (1e 1975); Blackwell Scientific Publications (2e 1994); Blackwell Publishing (3e 2004)
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Library of Congress Cataloging‐in‐Publication Data
Name: Johnson, R. P. (Roger Paul), author.
Title: Composite structures of steel and concrete : beams, slabs, columns and frames for buildings / Roger P. Johnson, University of Warwick, UK.
Description: 4th edition. | Hoboken, NJ, USA : Wiley [2019] | Includes bibliographical references and index. |
Identifiers: LCCN 2018016256 (print) | LCCN 2018016962 (ebook) | ISBN 9781119401414 (Adobe PDF) | ISBN 9781119401384 (ePub) | ISBN 9781119401438 (hardcover)
Subjects: LCSH: Composite construction. | Building, Iron and steel. |
Concrete construction.
Classification: LCC TA664 (ebook) | LCC TA664 .J63 2018 (print) | DDC
624.1/821–dc23
LC record available at https://lccn.loc.gov/2018016256
Cover Design: Wiley
Cover Image provided by Severfield plc
This volume provides an introduction to the theory and design of composite structures of steel and concrete. Readers are assumed to be familiar with the elastic and plastic theories for the analysis for bending and shear of cross‐sections of beams and columns of a single material, such as structural steel, and to have some knowledge of reinforced concrete. No previous knowledge is assumed of the concept of shear connection within a member composed of concrete and structural steel, nor of the use of profiled steel sheeting in composite slabs. Shear connection is covered in depth in Chapter 2 and Appendix A, and the principal types of composite member in Chapters 3, 4 and 5.
Limit state design philosophy has been used in British codes for structural design for over 40 years. Some familiarity is assumed with ultimate limit states (ULS) and serviceability limit states (SLS), which are the main subject here. The accidental limit state of exposure to fire, important in buildings, is the subject of Chapter 6.
All material of a fundamental nature that is applicable to structures for both buildings and bridges is included, plus more detailed information and a fully worked example relating to buildings. Subjects mainly applicable to bridges, such as box girders and design for fatigue, are not included. The design methods are illustrated by calculations. For this purpose a single structure, or variants of it, has been used throughout the volume. The reader will find that its dimensions, its loadings, and the properties of its materials soon remain in the memory. Its foundations are not included. The design is not optimal, because one object here has been to encounter a wide range of design problems, whereas in practice one seeks to avoid them.
This volume is intended for undergraduate and graduate students, for university teachers, and for engineers in professional practice who seek familiarity with composite structures. Most readers will seek to develop the skills needed both to design new structures and to predict the behaviour of existing ones. This is now always done using guidance from a code of practice. The Eurocodes replaced the former British codes in 2010. Their use is required for building and bridge structures that are publicly funded. Use of the former codes continues for some smaller projects, for private clients, but their methods are increasingly out‐of‐date.
All the design methods explained and used in this volume are those of the current Eurocodes, except where expected revisions are used. In the worked examples, both tensile and compressive forces and strengths of materials are given as positive numbers, distinguished in symbols by subscripts ‘t’ or ‘c’ or by words such as ‘tensile’. A rigorous tension‐positive convention has been used only in Appendix A. Elsewhere, the presentation is in the style normally used for hand calculations in practice.
The British versions of the Eurocodes are numbered BS EN 1990 to 1999, subdivided into 58 Parts. The national versions of the Eurocodes were published by each national standards organization in its chosen language, between 2002 and 2010. Those most relevant to this book are in the list of References, beginning ‘BSI’. Similarly, the German standards organization (for example) has published DIN EN 1990, and so forth. Each code or part includes a National Annex, for use for design of structures to be built in the country concerned. Apart from these annexes and the language used, the codes are identical and are applicable in all countries that are members of the European Committee for Standardization, CEN.
The withdrawal of the UK from the European Union is not expected to alter the link between the British Standards Institution and CEN, or the status of the Eurocodes in the UK. CEN already includes non‐EU countries, such as Switzerland and Norway.
The Eurocode for composite structures, EN 1994, is based on recent research and current practice. It has much in common with the earlier national codes in Western Europe, but its scope is far wider. Two of its three Parts are used here, with the shortened names: EC4‐1‐1, General rules and rules for buildings, and EC4‐1‐2, Structural fire design. The third Part, EC4‐2, is for bridges. Eurocode 4 has many cross‐references to other Eurocodes, particularly:
The Eurocodes refer to other European (EN) and International (ISO) standards, for subjects such as products made from steel, and execution. ‘Execution’ is an example of a word used in Eurocodes with a particular meaning that has replaced the word previously used: construction (BSI, 2011). Other examples will be explained as they occur.
The cost of purchasing Eurocodes is quite high. Employers provide them for their staff, and students have access via university libraries. Designers' guides or handbooks to the Eurocodes have been published in the UK by the Institution of Civil Engineers (e.g. Beeby and Narayanan, 2005; Gardner and Nethercot, 2004; Johnson, 2012), the Institution of Structural Engineers, and by associations such as the Steel Construction Institute and the Concrete Society. They start from a higher level of prior knowledge than is assumed here.
The purpose of this book is to present, explain and use the theories, structural models and assumptions used in Eurocode 4, and those needed from Eurocodes 1, 2 and 3. There are few cross‐references to Eurocode clauses, and access to them, although helpful, is not assumed.
Readers should not assume that the worked examples are fully in accordance with the Eurocodes as implemented in any particular country. The examples are not comprehensive, and Eurocodes give only ‘recommended’ values for some numerical values, especially the γ and ψ factors. The recommended values, which are used here, were subject to revision in National Annexes, but few of them were changed in the UK.
The first major revision of the Eurocodes began in 2015, with publication expected in the early 2020s. There will be important additions to the scope of Eurocode 4. Examples are: beams with large web openings, slim‐floor construction, use of precast floor slabs, concrete dowel shear connectors, and partial shear connection for beams supporting composite slabs. These subjects are included here, and their consequences for the design examples are explained.
The principal author of the book is R.P. Johnson, who has for many decades shared the challenge of work on Eurocode 4 with other members of committees of BSI and of CEN. The substantial contributions made by these colleagues and friends to his understanding of the subject are gratefully acknowledged. Chapter 6 is contributed by Yong C. Wang who has greatly benefited from interactions with other members of CEN working groups and the project team who are responsible for revising EN 1994‐1‐2. Both authors are contributing to the revisions of Eurocode 4. These are under discussion at present, and will have to be consistent with the revisions of other Eurocodes. Hence, the references given here to expected changes should be considered as the authors' best understanding of the current state of development of Eurocode 4. Responsibility for what is presented here rests with the writers, who would be glad to be informed of any errors that may be found.
November 2017
Roger P. Johnson and Yong C. Wang
The symbols used in this volume are, wherever possible, the same as those in EN 1994 and in the Designers' Guide to EN 1994‐1‐1 (Johnson, 2012). They are based on ISO 3898:1987, Bases for design of structures – Notation – General symbols. They are more consistent that those used in the British codes, and more informative. For example, in design one often compares an applied ultimate bending moment (an ‘action effect’ or ‘effect of action’) with a bending resistance, since the former must not exceed the latter. This is written
where the subscripts E, d, and R mean ‘effect of action’, ‘design’, and ‘resistance’, respectively. For clarity, multiple subscripts are often separated by commas (MR,d would be an example); but there are many exceptions, as the examples above show.
For longitudinal shear, the following should be noted:
For subscripts, the presence of three types of steel leads to the use of ‘s’ for reinforcement, ‘a’ (from the French ‘acier’) for structural steel, and ‘p’ or ‘ap’ for profiled steel sheeting. Another key subscript is k, as in
Here, the partial factor γF is applied to a characteristic bending action effect to obtain a design value, for use in a verification for an ultimate limit state. Thus ‘k’ implies that a partial factor (γ) has not been applied, and ‘d’ implies that it has been. This distinction is made for actions and resistances, as well as for the action effect shown here.
Other important subscripts are:
The word ‘resistance’ replaces the widely‐used ‘strength’, which is reserved for a property of a material or component, such as a bolt.
A useful distinction is made in most Eurocodes, and in this volume, between ‘resistance’ and ‘capacity’. The words correspond respectively to two of the three fundamental concepts of the theory of structures, equilibrium and compatibility (the third being the properties of the material). The definition of a resistance includes a unit of force, such as kN, while that of a ‘capacity’ does not. A capacity is typically a displacement, strain, curvature, or rotation.
In the Eurocodes, x is an axis along a member. A major‐axis bending moment My acts about the y axis, and Mz is a minor‐axis moment. This differs from previous practice in the UK, where the major and minor axes were xx and yy, respectively.
The SI system is used. A minor inconsistency is the unit for stress, where both N/mm2 and MPa (megapascal) are found in the codes. Similarly, kN/mm2 corresponds to GPa (gigapascal). The unit for a coefficient of thermal expansion may be given as ‘per °C’ or as ‘K‐1’, where K means kelvin, the unit for the absolute temperature scale. The convention of sign is explained in the Preface.
The list of symbols in EN 1994‐1‐1 extends over eight pages, and does not include many symbols in clauses of other Eurocodes to which it refers. The list can be shortened by separation of main symbols from subscripts. In this book, commonly‐used symbols are listed here in that format. Rarely‐used symbols are defined where they appear. Fire‐related symbols from EN 1994‐1‐2 are listed in Chapter 6.