Truss Bridges
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      The Truss Bridge    

    Trusses are used to stiffen and support a bridge by distributing the loads and forces acting upon the bridge based on the positions of the vertical, horizontal and diagonal chords.  They are based on triangular configurations.  How those chords are arranged identifies the type of truss.  Trusses are also used on cantilever bridges and to support the decks in suspension bridges.  Trusses are "through trusses" when the truss is above the deck, and "deck trusses" when they are underneath, supporting the truss.  Three early American bridgebuilders--Timothy Palmer (1751-1821), Lewis Wernwag (1770-1843) and Theodore Burr (1771-1822) built truss bridges and are known as the "Inspired Carpenters." Palmer is credited among the first to cover the the truss, leading to construction of covered bridges in the United States.  The truss bridge was described as long ago as the sixteenth century by Andrea Palladio in his Four Books on Architecture.  

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    The Betsy Ross Bridge, across the Delaware River between Philadelphia, Pennsylvania and Pennsauken, New Jersey, is relatively recent, constructed between 1969 and 1976.  According to the Delaware River Port Authority, this bridge is "the first U.S. bridge named after a woman." Over 29000 tons of structural steel were used for the bridge and its approaches.  It is a continuous through truss bridge.  Its length, from abutment to abutment, is given at 8,485 feet.  The main span is 729 feet long, and the two side spans are 364½ feet each.  The equilateral triangles are typical of the Warren Truss design, which is common for simple and continuous truss bridges.
To see different types of truss bridges, click on these links: Warren Truss Bridges Pratt Truss Bridges Iron Truss Bridges Miscellaneous Types of Truss Bridges A Sampling of Truss Bridges

 

 

All text and images on these pages copyright (c) Steven M. Richman 1997-2007.  All rights reserved.