Bridges – Suspension – Simple system
Patent
1983-12-28
1986-12-30
Leppink, James A.
Bridges
Suspension
Simple system
14 9, 14 21, 52 87, 52226, 52227, E01D 1100
Patent
active
046317724
DESCRIPTION:
BRIEF SUMMARY
This invention is in part disclosed in a co-pending application entitled Tension Arch Structure, Ser. No. 372,805, filed Apr. 28, 1982, now U.S. Pat. No. 4,464,803, issued Aug. 14, 1984.
BACKGROUND OF THE INVENTION
1. Field of Invention
The tension arch is a structural system useful in bridges, buildings and other structures which must support loads across a span.
2. Description of Prior Art
The bridge embodiment of the tension arch has elements of many types of prior bridges. For this reason, each of the major types of bridge structures is discussed. Bridge structures are conventionally divided into one of three types: Beam, arch and suspension. Two additional types, trusses and cantilevers are often called composites or combinations of these three types. All of these classifications are more or less arbitrary.
The Beam
This bridge, shown in FIG. 1A, is undoubtedly the oldest bridge. At its most basic it is a tree fallen across a stream. It is supported at either end, and the strength of the beam member itself supports the dead weight of the beam and the weight of the live load.
The steel I-beam bridge is quite common today. The web or vertical panel provides the strength to resist the shear, while the flanges or top and bottom panels resist the bending moment. These bridges could, however, also be called truss bridges with a solid web between the upper and lower chords.
The Arch
The Romans gave the arch bridge to western civilization. This bridge, shown in FIG. 1B, was made of stone or brick, often without mortar. The arch was semi-circular, rarely over 80 feet in diameter or span, supported by piers of about a third the span in thickness. Each arch was structurally independent of the next.
The best preserved of these bridges in Italy is the Pons Augustus in Rimini, built about 20 B.C. One of the largest is the three tier aqueduct at Pont du Gard, France. For a millenium, this design was the state of the art, as witnessed by the London Bridge, built in 1209. The soundness of the design is shown by the centuries these bridges have been in use.
In the Renaissance builders began to flatten the bridge arch, or widen the span between piers, as shown in FIG. 1C. Each span however, was free standing, being supported on its two piers. An example is the Santa Trinita Bridge in Florence, built in 1569.
For hundreds of years Gothic cathedrals had used flying buttresses to transfer the horizontal thrust of an arch beyond the pier supporting the vertical load. This idea was finally adopted for bridges by Jean Rodolphe Perronet. His Pont de Neuilly bridge in France, built in 1774, had elliptical arches spanning 120 feet where each of the five arches supported part of the horizontal thrust of the adjoining arch.
Cantilever
This type of bridge, shown in FIG. 1D, was widely used in the Orient several centuries ago. In the seventeenth century the Wanchpore Bridge in Bhutan was built, with a main span of over one hundred feet. Timbers were corbelled out from each abutment and the central interval was spanned by a light beam.
In the 1860's the Germans invented the modern metal cantilever truss bridge. The Cooper River Bridge in Charleston, S.C., built in 1920, is an example, and has a main span of 1,050 feet. The cantilever becomes a joined arch when the two arms touch as in the viaduct at Viaur, France.
The Suspension Bridge
Rope suspension bridges antedate recorded history. In the seventh century iron chains were used as cables in the Orient. The first chain cable bridge in Europe was the Winch Bridge over the Tees in England, built in 1491. All of these bridges laid the flooring on the cable.
In 1801 an American, James Finley, suspended a level roadway from the chain cables, making the modern suspension bridge shown in FIG. 1E. In 1816 he obtained a patent on a bridge using wire cables instead of iron chains. The United States retained the lead in suspension bridges with the 1,000 foot span bridge built in 1848 at Wheeling, W. Va., by Eliot, and the 1,600 foot span Brooklyn Bridge of John Roebling built in
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Leppink James A.
Letchford John F.
Roberts John T.
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