i Structural dynamics of earthquake engineering ii Related titles: Analysis and design of plated structures Volume 1: Stability (ISBN 978-1-85573-967-3) Steel-plated structures are used in a variety of marine and land-based applications, such as ships, off-shore platforms, power and chemical plants, box-girder cranes and bridges. This first volume in a two-volume sequence considers the various types of buckling that plated structures are likely to encounter. Chapters also review buckling in a range of materials from steel to differing types of composite. The book discusses the behaviour of differing types of components used in steel-plated structures as well as curved, stiffened, corrugated, laminated and other types of plate design. Together with its companion volume, this is an essential reference in the design, construction and maintenance of plated structures. Analysis and design of plated structures Volume 2: Dynamics (ISBN 978-1-84569-116-5) This second of two volumes on plated structures reviews dynamics, particularly vibration. Chapters review the behaviour of components such as beams and plates together with materials such as steel, ceramic–metal and other composites. Together with its companion volume, this important book summarises the wealth of research on understanding the behaviour of thin-walled (plated) components. It is an invaluable resource for all those concerned with the design, construction and service life of plated structures. Multiscale materials modelling: fundamentals and applications (ISBN 978-1-84569-071-7) The survival and success of many future industries relies heavily on engineered materials and products with improved performance available at relatively low cost. This demands not only the rapid development of new/improved processing techniques but also a better understanding and control of the materials themselves, their structure and properties. The aim of multiscale modelling is to predict the behaviour of materials from their fundamental atomic structure. This emerging technique is revolutionising our understanding of material properties and how they can be altered. This important book reviews both the principles of multiscale materials modelling and the ways it can be applied to understand and improve the performance of structural materials. Details of these and other Woodhead Publishing materials books can be obtained by: • visiting our web site at www.woodheadpublishing.com • contacting Customer Services (e-mail: [email protected]; fax: +44 (0) 1223 893694; tel.: +44 (0) 1223 891358 ext. 130; address: Woodhead Publishing Limited, Abington Hall, Granta Park, Great Abington, Cambridge CB21 6AH, UK) If you would like to receive information on forthcoming titles, please send your address details to: Francis Dodds (address, tel. and fax as above; e-mail: [email protected]). Please confirm which subject areas you are interested in. iii Structural dynamics of earthquake engineering Theory and application using MATHEMATICA and MATLAB S. Rajasekaran CRC Press Boca Raton Boston New York Washington, DC W OODHEAD PUBLISHING LIMITED Oxford Cambridge New Delhi iv Published by Woodhead Publishing Limited, Abington Hall, Granta Park, Great Abington, Cambridge CB21 6AH, UK www.woodheadpublishing.com Woodhead Publishing India Private Limited, G-2, Vardaan House, 7/28 Ansari Road, Daryaganj, New Delhi – 110002, India Published in North America by CRC Press LLC, 6000 Broken Sound Parkway, NW, Suite 300, Boca Raton, FL 33487, USA First published 2009, Woodhead Publishing Limited and CRC Press LLC © 2009, Woodhead Publishing Limited The author has asserted his moral rights. This book contains information obtained from authentic and highly regarded sources. Reprinted material is quoted with permission, and sources are indicated. Reasonable efforts have been made to publish reliable data and information, but the author and the publishers cannot assume responsibility for the validity of all materials. 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Typeset by Replika Press Pvt Ltd, India Printed by TJ International Limited, Padstow, Cornwall, UK v To my wife Saraswathi vi vii Contents Programs available in this book xvii Preface xxi Acknowledgements xxiii 1 Introduction to dynamics 1 1.1 Introduction 1 1.2 Different types of dynamic loads 2 1.3 Difference between dynamic and static problems 2 1.4 Methodology 4 1.5 Types of vibration 5 1.6 Further reading 6 Part I Structural dynamics in relation to earthquakes 2 Free vibration of single-degree-of-freedom systems (undamped) in relation to structural dynamics during earthquakes 9 2.1 Introduction 9 2.2 Formulation of the equation of motion 9 2.3 Simple harmonic theory 10 2.4 Newton’s second law 14 2.5 Simple pendulum 19 2.6 Comparison of simple harmonic motion and uniform circular motion 21 2.7 Energy method 22 2.8 Rayleigh method 24 2.9 D’Alembert’s principle 24 2.10 Free vibration of rigid bodies without damping 25 2.11 Program 2.1: MATLAB program to draw displacement, velocity and acceleration with respect to time 28 viii Contents 2.12 Program 2.2: MATHEMATICA program to draw displacement, velocity and acceleration with respect to time 29 2.13 Free vibration of structural systems 32 2.14 Exercises 39 2.15 Further reading 42 3 Free vibration of single-degree-of-freedom systems (under-damped) in relation to structural dynamics during earthquakes 43 3.1 Introduction 43 3.2 Damping free vibrations 43 3.3 Logarithmic decrement 47 3.4 Hysteresis damaping 53 3.5 Coulomb damping 55 3.6 Numerical method to find response due to initial conditions only 58 3.7 Program 3.1: MATLAB program for free vibration of under-damped SDOF systems 59 3.8 Program 3.2: MATHEMATICA program for free vibration of damped SDOF systems 60 3.9 Summary 66 3.10 Exercises 66 3.11 Further reading 67 4 Forced vibration (harmonic force) of single-degree- of-freedom systems in relation to structural dynamics during earthquakes 68 4.1 Forced vibration without damping 68 4.2 Beating phenomenon 73 4.3 Resonance 75 4.4 Forced vibration with damping 77 4.5 Program 4.1: MATHEMATICA program to find displacement response of under-damped system subjected to sinusoidal loading 79 4.6 Recurrence formula of Wilson 81 4.7 Program 4.2: MATLAB program for finding response due to harmonic force 82 4.8 Vector relationship in forced vibration 83 4.9 Rotating imbalance 87 4.10 Transmissibility (force isolation) 92 4.11 Program 4.3: MATLAB program to compute MF, MX/me and TR 93 Contents ix 4.12 Effectiveness of foundation 94 4.13 Displacement isolation 95 4.14 Vibration-measuring instruments 96 4.15 How to evaluate damping in SDOF 97 4.16 Response to ground acceleration 99 4.17 Exercises 101 4.18 Further reading 103 5 Response of structures to periodic dynamic loadings 105 5.1 Introduction 105 5.2 Fourier analysis 106 5.3 Program 5.1: MATHEMATICA program to determine Fourier coefficients of forcing function 111 5.4 Response to periodic excitation 115 5.5 Program 5.2: MATHEMATICA program for finding the response to a periodic function 116 5.6 Frequency domain analysis 121 5.7 Alternative form of Fourier series 122 5.8 Program 5.3: MATLAB program to evaluate amplitudes and phase angles 124 5.9 Expression of forcing function using complex variable approach 127 5.10 Discrete fourier transform (DFT) and fast fourier transform (FFT) 131 5.11 Gibbs phenomenon 132 5.12 Summary 133 5.13 Exercises 133 5.14 Further reading 134 6 Response of structures to impulse loads 136 6.1 Introduction 136 6.2 Impulsive loading – sine wave 136 6.3 Program 6.1: MATLAB program to obtain maximum response for half sine cycle pulse 140 6.4 Response to other arbitrary dynamic excitation 141 6.5 Duhamel integral 146 6.6 Response to arbitrary dynamic excitation 148 6.7 Response spectrum 157 6.8 Program 6.3: MATLAB program to find the response spectrum for any load pulse 158 6.9 Laplace transform 163 6.10 Program 6.4: MATHEMATICA program for Laplace transform method 165