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Countryside Books - Trevor Yorke

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149 pages

English

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Bridges are the keys to communication and transport. But though functional, they also have an aesthetic and environmental value. Graceful and spectacular, they evoke a wide range of emotions. Yet few have visitor centres and the public's obvious questions-such as how they were built; what a particular part does; why they don't fall down-are not often answered in simple terms. In this book, Trevor Yorke uses diagrams, drawings and photographs to explain the basic principals of their construction and style. It divides into five sections-the first is a general background; then it discusses the arched bridges; then come other, later forms of bridge; fourthly viaducts and aqueducts; finally a quck reference guide with a list of bridges to visit. The book will certainly expand your knowledge of bridges and hopefully leave you with a greater appreciation of them.

Sujets

History

Architecture

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Publié par	Countryside Books
Date de parution	27 mars 2008
Nombre de lectures	0
EAN13	9781846748561
Langue	English
Poids de l'ouvrage	9 Mo

Informations légales : prix de location à la page 0,0224€. Cette information est donnée uniquement à titre indicatif conformément à la législation en vigueur.

Extrait

BRIDGES EXPLAINED
What they do and How they Work

_____________ TREVOR YORKE ______________

COUNTRYSIDE BOOKS
NEWBURY, BERKSHIRE
First published 2008 © Trevor Yorke, 2008
All rights reserved. No reproduction permitted without the prior permission of the publisher:
COUNTRYSIDE BOOKS 3 Catherine Road Newbury, Berkshire
To view our complete range of books, please visit us at www.countrysidebooks.co.uk
ISBN 978 1 84674 079 4
Drawings and photographs by the author except for Fig.1.2: Julie Pointon; Figs. 6.4, 6.15, 8.12, 8.13, 8.14, 8.17, 10.7, 10.12, 10.13, 11.6 and 11.14 (bottom): Stan Yorke; Fig. 9.19 (top): Eric Brady
Thanks are also due to the Property Department of the Manchester Ship Canal Company for all their help with information on the Barton Swing Aqueduct
Produced through MRM Associates Ltd., Reading Typeset by Jean Cussons Typesetting, Diss, Norfolk Printed by Cambridge University Press
All material for the manufacture of this book was sourced from sustainable forests
C ONTENTS
I NTRODUCTION
SECTION I
Chapter 1
B UILDING B RIDGES
SECTION II
Chapter 2
R OMAN AND M EDIEVAL A RCHED B RIDGES
Chapter 3
T UDOR AND S TUART A RCHED B RIDGES
Chapter 4
G EORGIAN A RCHED B RIDGES
Chapter 5
C AST -I RON , S TEEL & C ONCRETE A RCHED B RIDGES
SECTION III
Chapter 6
B EAM , T RUSS AND G IRDER B RIDGES
Chapter 7
C ANTILEVER B RIDGES
Chapter 8
S USPENSION B RIDGES
Chapter 9
M OVING B RIDGES
SECTION IV
Chapter 10
V IADUCTS
Chapter 11
A QUEDUCTS
SECTION V
B RIDGES TO V ISIT
G LOSSARY
B IBLIOGRAPHY
I NDEX
Introduction

B ridges are a unique and vital form of structure. They are key to communication and transport and without them the country would not have developed and could not operate today. Bridges link com munities, making parts of a town or city that are separated by roads or rivers for example into one. Many draw in tourists, while their outline can feature as a regional logo or on coins, iconic symbols recognised worldwide.
For all their essential functionality bridges also have an aesthetic and environmental value. They are by their simple geometric form and structural use of material an attractive feature in the landscape. Stripped of decoration the graceful curve of an arch, the fine horizontal line of a beam or the elegant hung cables of a suspension bridge complement the surrounding countryside.
For me, bridges evoke a wide range of emotions: that very English deep set love of the rustic, the wonder of a spectacular modern structure vanishing into the mist, and the shear terror when crossing anything more than fifty feet below! It was whilst spending hours studying bridges at the drawing board that I started to ask questions about how they were built, what exactly a particular part did, and why they didn’t fall down! The answers, however, could be hard to find. Few bridges have visitor centres and books on the subject seem rather sparse despite the public’s obvious interest. It was this gradual frustration with the lack of easily accessible and under standable information that I set out to learn for myself how, when, and why bridges were built
The book uses diagrams, drawings, and photographs to explain the basic principles of construction and styles of bridges so that the reader can better appreciate them, recognize how they work, and identify the period from which individual bridges probably date. The book is divided into four sections, the first giving a background to the subject. The second covers arched bridges, the third other forms of bridges, and the fourth viaducts and aqueducts. Finally, there is a list of all the bridges included in the book with a grid reference to accurately locate them, and a glossary of common terms.
Although it is hoped this book will expand your knowledge of the subject it is also intended to inspire you to visit different examples or look again at familiar bridges in a new light.
Trevor Yorke

www.trevoryorke.co.uk
To keep up to date with new projects and to post questions, go to Trevor-Yorke-Author on facebook and click ‘Like’
C HAPTER 1
Building Bridges

FIG. 1.1: The Tay Bridge Disaster: The famous collapse of what was then the world’s longest bridge highlights many of the difficulties which face all bridge builders.
A ferocious storm had suddenly built up on the east coast of Scotland during the afternoon of Sunday 28th December 1879. All had been calm six hours earlier but now, after dark, gale force winds were rattling down the Forth of Tay and over the city of Dundee. At the railway station staff were growing concerned that the train from Edinburgh due in at 7.15 pm had not arrived, and members of the public were adding to their anxiety by stating that they had seen a flash of fire along the new bridge on the approach to the station. This vast iron girder structure stretched over the estuary for nearly two miles. It had been opened only the previous year to much praise, especially for its designer, Thomas Bouch, who was subsequently knighted by the Queen after she herself had made the crossing.
In the blackness of this stormy winter’s night it was up to the station master and locomotive foreman to investigate. Having confirmed with the signalman that the missing train had entered the southern end of the bridge at 7.14 pm but that communication had since been lost with the signal box at the other end, there was nothing else to do but walk out along the bridge to find out what had happened. They stepped into the gloom and made their way to the middle of the bridge, finding it increasingly hard the further they went to keep their footing in the battering side winds. Then they were suddenly brought to a stop; the bridge in front of them had vanished. The men were standing above a pier with a huge void and the raging sea below. Convinced they could see a red light on the other end of the bridge which might be the missing train, the men were hopeful that it had been pulled up short of the fall, but, with the discovery of baggage washed ashore, it became clear on their return that it was not so.

FIG. 1.2: THE TAY RAIL BRIDGE, DUNDEE: In the right of this picture can be seen the remains of the brick and stone piers of the original bridge alongside the replacement bridge of 1887 to the left.
With daylight the full scale of the disaster unfolded. The whole central section of the bridge, 13 spans, known as the high girders, as they permitted a greater clearance below for the passage of shipping, had simply gone, taking the locomotive, carriages, and 75 pas sengers and crew with them. Boats had been out in the night but had failed to find any survivors, in part a terrible consequence of the compulsory locking of carriage doors on British railways at the time.
In the aftermath it was the respected engineer Thomas Bouch who took the blame for the disaster. Because the surveys of the sea bed had proved to be inaccurate, he had changed his design from one using brick piers to one with iron columns in order to lighten the load on the foundations. This new structure was tall and narrow, with inadequate cross-bracing to give the structure stability, so that when it was hit by a strong cross wind, as happened on this night, the ironwork failed and the structure toppled into the sea. Bouch, who at the time had already laid the foundation stone for his next project, the Forth Rail Bridge, found his career in ruins and he died later the following year, reportedly a broken man.
A new bridge across the Tay was built alongside the old one, this time with a double track, thus creating a wider and substantially stronger structure, which stands to this day. The brick pier bases of the old bridge were retained to act as breakwaters for the new structure upstream of it, and some of the girders were re-used, albeit with additional strengthening. Incredibly, the locomotive which plunged into the sea on that fateful day was salvaged and repaired, and carried on in service for another 25 years, although it was always known to railway men as ‘the Diver’!
ENGINEERING A BRIDGE
The story of this well-known disaster highlights the difficulties which face all bridge builders and are worth explanation before looking at the different types of structures in the following sections. Whether it is simply a stone or timber beam across a brook or the latest suspension bridge spanning an estuary, the designer has to tackle the same basic problems. Where is it best to build it? What are the forces which will act upon it? What materials are suitable for it? How will it be built?
Location
The siting of a bridge is one of the most important decisions in the design process. The abutments and piers or towers need to be built upon a firm footing, and so discovering the geology of the land and the river bed is the first step and this will have an effect upon the choice of structure and materials used for the bridge. Although the narrowest part of the river may seem the ideal site, a place where the bedrock or best ground is nearest to the surface is more likely to be chosen. Often this will be where a previous structure and/or ford stood, as this will indicate where the river bed and flow is suitable and will tie in with the existing road network. The ford can also continue in use for heavier vehicles to reduce wear on the new bridge.
The sides of a valley or the embankments on the approach to a bridge, viaduct, or aqueduct must also be carefully studied and engineered. At Ironbridge the notoriously unstable geology of the gorge caused the southern approach to slide and fail, and it had to be replaced only a few decades after the bridge was opened. The embankments leading up to a bridge also exert a lateral force as they slowly settle and slide over time and so abutments which wrap around the exposed end need to be substantial enough and buttressed to resist this gradual spread.

FIG. 1.3: The form of the