David Yeomans - How Structures Work: Design and Behaviour from Bridges to Buildings

1. Chapter 07

1. Preface
2. Chapter 01
3. Chapter 02
4. Chapter 03
5. Chapter 04
6. Chapter 05
7. Chapter 06
8. Chapter 07
9. Chapter 08
10. Chapter 09
11. Appendix

Second edition

David Yeomans

This edition first published 2016
2016 David Yeomans
First edition David Yeomans 2009.

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Library of Congress Cataloging-in-Publication Data

Yeomans, David T.
How structures work : design and behaviour from bridges to buildings / David Yeomans. Second edition.
pagescm
Includes bibliographical references and index.

ISBN 978-1-119-01227-6 (pbk.)
1.Structural engineering. I.Title.
TA633.Y46 2015
624.1dc23

2015022633

A catalogue record for this book is available from the British Library.

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Cover image: Cameron Scott

For Louise, Jane, Julia and my sister

The dedication of this book requires some explanation because, although it has been written to be suitable for architectural students, it was not originally conceived as such. The dedicatees include two archaeologists and an antiquarian book dealer. The idea for the book goes back further than I care to remember. Visiting an archaeologist friend, I picked up a book on Greek architecture, and it became apparent that the authors understanding of structure and construction lacked something. Dont you think, Louise, that it would be a good idea for archaeologists to learn something about building structures? Yes it would and so the seed was sown. The idea was simply that something on building structures might be useful for people with little or no mathematics but whose work or subject of study involves understanding buildings.

Many years later, Jane Grenville asked me if I could give some classes to her masters course on buildings archaeology at York University. Structures for archaeologists? Ive always wanted to try teaching that. And so the text for this began with the notes for that class. Working up the text into this form was pushed aside by other things until Julia, a dealer in antiquarian engineering books, said that she had asked the late Professor Skempton if he could teach her some structures. Hed claimed it would be difficult because the subject is highly mathematical. She thought this nonsense, pointing out that she frequently heard engineers discussing structures but they never used any mathematics. Of course, shes right; we seldom do when thinking about structures. The general experience is that one manages with a few simple concepts. Given the rule for static equilibrium, the triangle of forces and some ideas about moments and elasticity, one has the basic bag of tools that will cope with most situations. What one needs to add to this to make a designer, rather than a mere stress analyst, is an understanding of the properties of the materials that make up the structures we build, because no real understanding is possible without that. How then to provide the simple bag of tools? Goaded by Julias demands, I determined to tackle the problem.

What started as something for archaeologists, architectural historians or even the interested layperson (represented by my sister), and still remains suitable for that audience, was then developed at the suggestion of my commissioning editor to include material that would make it an architectural students text. Here, we see what might be described as a non-threatening approach to something that is normally seen as a highly technical subject, the idea for a method coming from my experience of starting to learn Spanish.

I was taught French and Latin at school, starting with the grammar; and that is how we commonly teach the theory of structures. We begin with the grammar and only apply it to real structures afterwards, the transition sometimes being difficult for students. Today, languages are often taught through communication. The Spanish teacher introduced herself in the first class with Me llamo Maria. Como te llamas? Tone of voice indicated a question, and one quickly grasped what the reply should be without realising one was using a reflexive verb a difficult piece of grammar because it is something that does not exist in English. Why then not teach structures in a similar way? Begin with simple structures that are easy to understand from common experience and build up the grammar, that is, the theoretical ideas, only as necessary. This might even be something that would appeal to engineers because it sometimes seems as if they have learnt a number of abstract concepts without grasping how they apply to real structures.

I only wish I had thought of this approach while I was teaching architectural students because no matter how simple we tried to make the subject for them they probably regarded structural analysis as a series of mind-numbing routines. The evidence was there in what I called my Christmas test. In the last class before the Christmas vacation I would present first-year students with a puzzle that I first came across in Meccano Magazine when I was 10 years old:

I have to weigh a lorry, but it is too long for the weighbridge. I put the front wheels on the weighbridge and take a reading. I then drive it forwards so that only the back wheels are on and take another reading. I add the two readings together. Do I have the weight of the lorry?