کتاب Structural Dynamics

This book aims to provide a concise and accessible introduction to the principles and underlying theory of structural dynamics. It is aimed principally at students of civil engineering but should also be of interest to other engineering disciplines with an interest in vibrations. It is based on my experience in teaching undergraduates in engineering science at Oxford University, and also on a series of short courses I have given over many years, aimed at civil engineering practitioners with little prior experience of dynamics.
Dynamic behaviour of structures has grown in prominence over recent decades and is now covered to some extent in most engineering courses. The importance of dynamic response to extreme environmental loads such as earthquakes has been recognised for some time, and is an essential topic for engineers working in parts of the world where these threats are prevalent. Increasingly, however, as more slender, daring structures are built, vibration problems are spreading to all parts of the world and to many different types of structures.
At one end of the spectrum, an engineer might be concerned with preventing collapse of a major suspension bridge due to aero-elastic instability in high winds. At the other, the issue might be minimising vibrations due to a single human footstep in highly motion-sensitive environments such as clean rooms. The range of possible load cases is too broad to discuss all of them here, but of course, they all share the same theoretical underpinning, which is the focus of this text.
We begin with an introductory chapter, Chapter 1, highlighting some key examples of dynamic behaviour, and introducing some of the language and mathematics of dynamics. Chapter 2 then introduces most of the important principles of structural dynamics by focusing on single-degree-of-freedom systems – idealisations of structures in which the motion is described by only one displacement variable. In Chapter 3, we look at how this basic theory can be extended to multi-degree-of-freedom systems. The methods introduced here are the basis of finite element dynamic analysis software routinely used in design offices. Chapter 4 looks at vibrations of continuous systems such as beams, where an explicit solution can often be obtained by solving the governing differential equations, without recourse to numerical methods. It also explains how to create approximate single-degree-of-freedom representations of continuous or distributed systems.
Many dynamic loads such as extreme wind and earthquake are likely to cause structural damage, normally in the form of localised yielding in structural members, causing a loss of stiffness. This is the subject of Chapter 5, which presents a variety of approaches to nonlinear dynamic analysis. Finally, in Chapter 6 the topic of Fourier analysis and random vibrations is introduced. This is a difficult topic and not one that has yet entered the civil engineering mainstream, but its importance is likely to grow in the near future. While dynamics is unavoidably one of the more mathematically demanding branches of structural analysis, I have tried to keep the maths in the main text as simple and sparse as possible, with the focus on the underlying principles. The main mathematical techniques involved are briefly summarised in a set of appendices.
While I hope I have come up with some novel and helpful ways of presenting the concepts of structural dynamics, I make no claims to originality of the material presented, all of which has been in the public domain for some time. My aim here has been to present key concepts in a clear and concise way to introduce the topic. I have provided an extensive reading list for those wishing to know more, or delve deeper.
Of course, writing any book is a major undertaking that requires the support of numerous individuals and institutions. I am grateful to colleagues and students at the University of Oxford’s Department of Engineering Science and at New College, Oxford, who for many years have provided such a stimulating working environment. Over the years, I have benefitted greatly from interactions with many outstanding engineers who have shaped my views on the subject. I thank them all, but wish to mention in particular Peter McFadden, Tony Blakeborough and Edmund Booth. Staff at Taylor & Francis have been patient and encouraging throughout the rather long gestation period of this work, and I am grateful in particular to Tony Moore and Amber Donley for their always calm and constructive input. Last but not least, the love and support of my wife EJ and son Rowan have been vital to the completion of this work.
Photos of the Tacoma Narrows Bridge are reproduced by permission of University of Washington Libraries, Special Collections, ref. WA21424. Other photos within the text are my own.