A Short Guide to the Types and Details of Constructing a Suspension Bridge - Including Various Arrangements of Suspension Spans, Methods of Vertical Stiffening and Wire Cables Versus Eyebar Chains

By D. B. Steinman

This book contains classic material dating back to the 1900s and before. The content has been carefully selected for its interest and relevance to a modern audience.

• Language: English
• Publisher: Read Books Ltd.
• Release date: Sep 13, 2016
• ISBN: 9781473357815

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A Short Guide to the Types and Details of Constructing a Suspension Bridge

Including Various Arrangements of Suspension Spans, Methods of Vertical Stiffening and Wire Cables Versus Eyebar Chains

By

D. B. Steinman

Copyright © 2011 Read Books Ltd.

This book is copyright and may not be reproduced or copied in any way without the express permission of the publisher in writing

British Library Cataloguing-in-Publication Data

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Contents

TYPES AND DETAILS OF CONSTRUCTION

TYPES AND DETAILS OF CONSTRUCTION

1. Introduction.—The economic utilization of the materials of construction demands that, as far as possible, the predominating stresses in any structure should be those for which the material is best adapted. The superior economy of steel in tension and the uncertainties involved in the design of large-sized compression members point emphatically to the conclusion that the material of long-span bridges, for economic designs, must be found to the greatest possible extent in tensile stress. This requirement is best fulfilled by the suspension-bridge type.

The superior economy of the suspension type for long-span bridges is due fundamentally to the following causes:

1. The very direct stress-paths from the points of loading to the points of support.

2. The predominance of tensile stress.

3. The highly increased ultimate resistance of steel in the form of cable wire.

For heavy railway bridges, the suspension bridge will be more economical than any other type for spans exceeding about 1500 feet. As the live load becomes lighter in proportion to the dead load, the suspension bridge becomes increasingly economical in comparison with other types. For light highway structures, the suspension type can be used with economic justification for spans as low as 400 feet.

Besides the economic considerations, the suspension bridge has many other points of superiority. It is light, aesthetic, graceful; it provides a roadway at low elevation, and it has a low center of wind pressure; it dispenses with falsework, and is easily constructed, using materials that are easily transported; there is no danger of failure during erection; and after completion, it is the safest structure known to bridge engineers.

The principal carrying member is the cable, and this has a vast reserve of strength. In other structures, the failure of a single truss member will precipitate a collapse; in a suspension bridge, the rest of the structure will be unaffected. In the old Niagara Railway Suspension Bridge (built 1855), the chords of the stiffening truss were broken (due to overloading) and repaired repeatedly, without interrupting the railroad traffic.

FIG. 25.—Brooklyn Bridge.

East River, New York, Span 1595 1/2 feet. Completed 1883.

There are two main classes of suspension bridges: those with suspended stiffening truss (Figs. 25 to 36), and those with overhead braced-chain construction (Figs. 37 to 41). For purpose of reference, there is given here (page 71) a comprehensive system of classification of suspension bridges, with mnemonic type symbols and outstanding examples.

2. Various Arrangements of Suspension Spans.—The simplest form of suspension bridge is a single span (Type 2F or 3F) with the cable carried past the towers as diagonal backstays (Figs. 27, 29). If side spans are added (Fig. 28), they are independent of the cable and of the main span. The single-span suspension bridge may be built either with or without a stiffening truss (Fig. 27).

FIG. 26.—Brooklyn Bridge. (Type 3SD).

Elevation, Plan, and Cross-section.

The next form is the bridge having three suspended spans (Types 0S, 1S, 2S, 3S). In this form, stiffening trusses (or girders) are indispensable. Only two towers are required, and each side span is about one-half the length of the main span (Figs. 10, 17, 25, 30, 33, 35).

If the main span is provided with a center hinge (in addition to end hinges), the three-span structure becomes statically determinate (Type 3S, Fig. 26). The side spans are suspended from the cable, but carry their loads as simple beams without affecting the stresses in the cable or