Download Why buildings stand up: the strength of architecture PDF

TitleWhy buildings stand up: the strength of architecture
ISBN 139780393014013
File Size17.2 MB
Total Pages310
Table of Contents
1 Structures
2 The Pyramids
3 Loads
4 Materials
5 Beams and Columns
6 Houses
7 Skyscrapers
8 The Eiffel Tower
9 Bridges
10 The Brooklyn Bridge
11 Form-Resistant Structures
12 The Unfinished Cathedral
13 Domes
14 Hagia Sophia
15 Tents and Balloons
16 The Hanging Sky
17 The Message of Structure
Document Text Contents
Page 155

The last expedient to free the navigable channel from impediments
during the arch (or truss) construction consists in building the arch on
its centering away from the site, then floating both centering and arch to
the site, and finally rapidly connecting the arch to its abutments. This
procedure is also most efficient when the waters under the bridge are
subject to short, violent floods or storms. The greatest of French concrete
engineers, Freyssinet, used this method to erect the monumental Plougastel
Bridge in northern France in 1920, lifting the heavy arch from the center­
ing by means of hydraulic jacks.

Page 156


To get a low bridge out of the way when river traffic must go
through, a variety of movable bridges has been invented. In one type
the center span consists of two trusses, each pivoted at one end and
capable of rotating upward when a boat needs to go by. It is called a
bascule bridge (Fig. 9.14). Or the center span may be lifted between
two end-towers, as in so many bridges in the New Jersey industrial area
and the large bridge over the Harlem River in New York, the first link
of the Triborough Bridge system (Fig. 9.15). Or finally the entire center
span of a bridge may be made to rotate horizontally on a central pier, as
in some of the bridges crossing the Harlem River, thus clearing two
separate channels on the sides of the pier (Fig. 9.16).



Concrete Bridges


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Some if not all of the bridge concepts born under the impact of the
railroads and executed in steel have been extended to concrete. The
trestle, built of wood at first and then of steel, has acquired a new
elegant expression in the long viaducts built in Europe. These consist
of hollow piers of reinforced concrete, at times 200 to 300 feet high,
over which runs a roadway of hollow reinforced or prestressed concrete
pipes of rectangular shape which are prefabricated on the river banks
and slid into position. In the latest application of this principle the
roadway pipes are extruded continuously, like spaghetti from a pasta
maker, from both ends of the bridge until they meet at midspan. The
simplicity, slenderness, and pure geometric shape of these viaducts make

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