Strength of Materials and Structures Fourth edition JOHN CASE M.A., F.R.Ae.S. Formerly Head of the Department of Applied Mechanics, Royal Naval Engineering College, Plymouth LORD CHILVER of Cranfield M.A., D.Sc., F.Eng., F.R.S. Formerly Vice Chancellor, Cranjield Institute of Technologv, and Professor of Civil Engineering, University College, London CARL T.F. ROSS B.S.C., Ph.D., D.Sc., C. Eng., F.R.I.N.A., M.S.N.A.M.E. Professor of Structural Dynamics, University of Portsmouth, Portsmouth A member of the Hodder Headline Group LONDON - SYDNEY AUCKLAND Co-published in North, Central and South America by John Wiley & Sons Inc., New York Toronto First published in Great Britain in 1959 as Strength of Materials Reprinted 1961, 1964 Second edition 197 1 Reprinted 1985, 1986 Third edition 1993 Reprinted 1992, 1994, 1995, 1997, 1998 Fourth edition published in 1999 by Arnold, a member of the Hodder Headline Group, 338 Euston Road, London NWl 3BH http://www.arnoldpublishers.com Co-published in North, Central and South America by John Wiley & Sons Inc., 605 Third Avenue, New York,NY 10158-0012 0 1999 John Case, A.H. Chilver and Carl T.F. Ross All rights reserved. No part of this publication may be reproduced or transmitted in any form or by any means, electronically or mechanically, including photocopying, recording or any information storage or retrieval system, without either prior permission in writing from the publisher or a licence permitting restricted copying. In the United Kingdom such licences are issued by the Copyright Licensing Agency: 90 Tottenham Court Road, London W l P 9HE. Whilst the advice and information in this book are believed to be true and accurate at the date of going to press, neither the authors nor the publisher can accept any legal responsibility or liability for any errors or omissions that may be made. British Library Cataloguing in Publication Data A catalogue record for this book is available from the British Library Library of Congress Cataloging-in-PublicationD ata A catalog record for this book is available from the Library of Congress ISBN 0 340 71920 6 ISBN 0 470 37980 4 (Wiley) 1 2 3 4 5 6 7 8 9 10 Commissioning Editor: Matthew Flynn Cover Designer: Terry Griffiths Printed and bound in Great Britain by J.W. Arrowsmith Ltd, Bristol What do you think about this book? Or any other Arnold title? Please send your comments to Acknowledgements I would like to thank my wge, Anne, and my children, Nicolette and Jonathan, who have suffered my nebulous number-crunching world of eigenvalue economisers and matrix manipulators over many years. My thanks are extended to Mrs. Joanna Russell and Mrs. Helen Facey for the considerable care and devotion they showed in typing this manuscript. CTFR, 1999 "Only when you climb the highest mountain, will you be aware of the vastness that lies around you. " Oscar Wilde, 1854-1 900. 0 0 0 c l cl CI 0 Chinese Proverb - It is better to ask a question and look a fool forfive minutes, than not to ask a question at all and be a fool for the rest of your life. Heaven and Hell - In heaven you are faced with an infinite number of solvable problems and in hell you are faced with an infinite number of unsolvable problems. Principal notation a length A area b breadth C complementary energy c wave velocity, distance D diameter d diameter E young’s modulus h depth F shearing force j number of joints G shearing modulus I length H force m mass, modular ratio, I second moment of area number of numbers J torsion constant n frequency, load factor, distance K bulk modulus p pressure L length q shearing force per unit length A4 bending moment r radius P force s distance Q force t thickness R force, radius u displacement S force v displacement, velocity T torque w displacement, load intensity, U strain energy force V force, volume, velocity x coordinate W work done, force y coordinate X force z coordinate Y force 2 section modulus, force a coefficient of linear expansion p density y shearing strain o direct stress 6 deflection T shearing stress E direct strain w angular velocity q efficiency A deflection 8 temperature, angle of twist @ step-function v Poisson’s ratio [k] element stiffness matrix [ K] system stiffness matrix [ m] elemental mass matrix [MI system mass matrix Note on SI units The units used throughout the book are those of the Systeme Internationale d’Unites; this is usually referred to as the SI system. In the field of the strength of materials and structures we are concerned with the following basic units of the SI system: length metre (m) mass kilogramme (kg) time second (s) temperature kelvin (K) There are two further basic units of the SI system - electric current and luminous intensity - which we need not consider for our present purposes, since these do not enter the field of the strength of materials and structures. For temperatures we shall use conventional degrees centigrade (“C), since we shall be concerned with temperature changes rather than absolute temperatures. The units which we derive from the basic SI units, and which are relevant to out fielf of study, are: force newton (N) kg .m .s-? work, energy joule (J) kg.m’.s-’ = Nm power watt (W) kg.m2.s-’ = Js-’ frequency hertz (Hz) cycle per second pressure Pascal (Pa) N.m-’ = lo-’ bar The acceleration due to gravity is taken as: g = 9 . 8 1 m ~ - ~ Linear distances are expressed in metres and multiples or divisions of 1 O3 of metres, i.e. Kilometre (km) IO’ m metre (m) l m millimetre (mm m In many problems of stress analysis these are not convenient units, and others, such as the centimetre (cm), which is lo-’ m, are more appropriate. The unit of force, the newton (N), is the force required to give unit acceleration (ms-’) to unit mass kg). In terms of newtons the common force units in the foot-pound-second-system (with g = 9.8 1 ms?) are 1 Ib.wt = 4.45 newtons (N) 1 ton.wt = 9.96 x IO’ newtons (N) x iv Note on SI units In general, decimal multiples in the SI system are taken in units of IO3. The prefixes we make most use of are: kilo k 1o 3 mega M 1o 6 gigs G 1o 9 Thus: 1 ton.wt = 9.96 kN The unit of force, the newton (N), is used for external loads and internal forces, such as shearing forces. Torques and bending of moments are expressed in newton-metres (Nm). An important unit in the strength of materials and structures is stress. In the foot-pound- second system, stresses are commonly expressed in Ib.wt/in2, and tons/in2. In the SI system these take the values: 1 Ib.wt/in2 = 6.89 x 103 N/m2 = 6.89 kN/m2 1 ton.wt/in2 = 15.42 x 106N/m2= 15.42 MN/m2 Yield stresses of the common metallic materials are in the range: 200 MN/m2 to 750 MN/m2 Again, Young's modulus for steel becomes: Estee=, 30 x 106 Ib.wt/in2 = 207 GN/mZ Thus, working and yield stresses will usually be expressed in MN/m2 units, while Young's modulus will usually be given in GN/m2 units. Preface This new edition is updated by Professor Ross, and whle it retains much of the basic and traditional work in Case & Chllver’s Strength of Materials and Structures, it introduces modem numerical techques, such as matrix and finite element methods. Additionally, because of the difficulties experienced by many of today’s students with basic traditional mathematics, the book includes an introductory chapter which covers in some detail the application of elementary mathematics to some problems involving simple statics. The 1971 ehtion was begun by Mr. John Case and Lord Chlver but, because of the death of Mr. John Case, it was completed by Lord Chlver. Whereas many of the chapters are retained in their 1971 version, much tuning has been applied to some chapters, plus the inclusion of other important topics, such as the plastic theory of rigid jointed frames, the torsion of non-circular sections, thick shells, flat plates and the stress analysis of composites. The book covers most of the requirements for an engineeringu ndergraduate course on strength of materials and structures. The introductory chapter presents much of the mathematics required for solving simple problems in statics. Chapter 1 provides a simple introduction to direct stresses and discusses some of the hdamental features under the title: Strength of materials and structures. Chapter 2 is on pin-jointed frames and shows how to calculate the internal forces in some simple pin-jointed trusses. Chapter 3 introduces shearing stresses and Chapter 4 discusses the modes of failure of some structural joints. Chapter 5 is on two-dimensional stress and strain systems and Chapter 6 is on thin walled circular cylindrical and spherical pressure vessels. Chapter 7 deals with bending moments and shearing forces in beams, whch are extended in Chapters 13 and 14 to include beam deflections. Chapter 8 is on geometrical properties. Chapters 9 and 10 cover direct and shear stresses due to the bending of beams, which are extended in Chapter 13. Chapter 11 is on beam theory for beams made from two dissimilar materials. Chapter 15 introduces the plastic hinge theory and Chapter 16 introduces stresses due to torsion. Chapter 17 is on energy methods and, among other applications, introduces the plastic design of rigid-jointed plane frames. Chapter 18 is on elastic buckling. Chapter 19 is on flat plate theory and Chapter 20 is on the torsion of non-circular sections. Chapter 21 is on thick cylinders and spheres. Chapter 22 introduces matrix algebra and Chapter 23 introduces the matrix displacement method. Chapter 24 introduces the finite element method and in Chapter 25 this method is extended to cover the vibrations of complex structures. CTFR, 1999 Contents Preface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . x Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xi Principal notation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xii ... NoteonSIunits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xiii Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 I. 1 Introduction 1.2 Trigonometrical definitions 1.3 Vectors and scalars 1.4 Newton’s Laws of Motion 1.5 Elementary statics 1.6 Couples 1.7 Equilibrium 1 Tension and compression: direct stresses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 1.1 Introduction 1.2 Stretching of a steel wire 1.3 Tensile and compressive stresses 1.4 Tensile and compressive strains 1.5 Stress-strain curves for brittle materials 1.6 Ductile materials 1.7 Proof stresses 1.8 Ductility measurement 1.9 Working stresses 1.10 Load factors 1.11 Lateral strains due to direct stresses 1.12 Strength properties of some engineering materials 1.13 Weight and stiffness economy of materials 1.14 Strain energy and work done in the tensile test 1.15 Initial stresses 1.16 Composite bars in tension or compression 1.17 Temperature stresses 1.18 Temperature stresses in composite bars 1.1 9 Circular ring under radial pressure 1.20 Creep of materials under sustained stresses 1.21 Fatigue under repeated stresses. 2 Pin-jointed frames or trusses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55 2.1 Introduction 2.2 Statically determinate pin-jointed frames 2.3 The method ofjoints 2.4 The method of sections 2.5 A statically indeterminate problem. 3 Shearingstress . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67 3.1 Introduction 3.2 Measurement of shearing stress 3.3 Complementary shearing stress 3.4 Shearing strain 3.5 Strain energy due to shearing actions. vi Contents 4 Joints and connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76 4.1 Importance of connections 4.2 Modes of failure of simple bolted and riveted joints 4.3 Efficiency of a connection 4.4 Group-bolted and -riveted joints 4.5 Eccentric loading of bolted and riveted connections 4.6 Welded connections 4.7 Welded connections under bending actions. 5 Analysis of stress and strain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94 5.1 Introduction 5.2 Shearing stresses in a tensile test specimen 5.3 Strain figures in mild steel; Liider’s lines 5.4 Failure of materials in compression 5.5 General two-dimensional stress system 5.6 Stresses on an inclined plane 5.7 Values of the principal stresses 5.8 Maximum shearing stress 5.9 Mohr’s circle of stress 5.10 Strains in an inclined direction 5.11 Mohr’s circle of strain 5.12 Elastic stress-strain relations 5.13 Principal stresses and strains 5.14 Relation between E, G and v 5.15 Strain ‘rosettes’ 5.16 Strain energy for a two-dimensional stress system 5.17 Three-dimensional stress systems 5.18 Volumetric strain in a material under hydrostatic pressure 5.19 Strain energy of distortion 5.20 Isotropic, orthotropic and anisotropic 5.21 Fibre composites 5.22 In-plane equations for a symmetric laminate or composite 5.23 Equivalent elastic constants for problems involving bending and twisting 5.24 Yielding of ductile materials under combined stresses 5.25 Elastic breakdown and failure of brittle material 5.26 Failure of composites. 6 Thin shells under internal pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152 6.1 Thin cylindncal shell of circular cross section 6.2 Thin spherical shell 6.3 Cylindrical shell with hemispherical ends 6.4 Bending stresses in thin-walled circular cylinders. 7 Bending moments and shearing forces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 169 7.1 Introduction 7.2 Concentrated and distributed loads 7.3 Relation between the intensity of loading, the shearing force, and bending moment in a straight beam 7.4 Sign conventions for bending moments and shearing forces 7.5 Cantilevers 7.6 Cantilever with non-uniformly distributed load 7.7 Simply-supportedb eams 7.8 Simply-supportedb eam carrying a uniformly distributed load and end couples 7.9 Points of inflection 7.10 Simply-supported beam with a uniformly distributed load over part of a span 7.11 Simply-supported beam with non-uniformly distributed load 7.12 Plane curved beams 7.13 More general case of bending of a curved bar 7.14 Rolling loads and influence lines 7.15 A single concentrated load traversing a beam 7.16 Influence lines of bending moment and shearing force. 8 Geometrical properties of cross-sections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 200 8.1 Introduction 8.2 Centroid 8.3 Centroid axes 8.4 Second moment of area (I) 8.5 Parallel axes theorem.