Suspension Bridges

Topics: Bridge, Bridges, John A. Roebling Suspension Bridge Pages: 3 (775 words) Published: February 1, 2008
Suspension Bridges A suspension bridge is a one where many cables are strung across two or more towers, which supports the majority of the bridge weight and force. The cables run from the towers to the anchorages.

Suspension bridges have benefited our everyday lives since John A. Roebling perfected the suspension bridge design in 1845 and built the Allegheny Suspension Bridge in Pittsburgh, Pennsylvania (Placzek). These bridges are better than previous bridges in many ways. Suspension bridges can span greater distances and are much cheaper than other types of bridges, such as beam bridges, which are simply constructed of beams supporting the deck of the bridge, they cannot span as long as these suspension bridges, and are more costly due to the amount of steel used. Without these bridges, some of today's largest gaps could not be crossed by use of a bridge.

Suspension bridges are no more than physics in action. The force of compression pushes down on the suspension bridge's deck, but because it is a suspended roadway, the cables transfer the compression to the anchorages which place the compression directly into the earth where they are firmly planted. The supporting cables, running between the two anchorages, are the recipients of the tension forces. The cables are stretched from the weight of the bridge and its traffic as they run from anchorage to anchorage. The anchorages are also under tension, but since they, like the towers are held firmly to the earth, the tension is placed into the earth. Almost all suspension bridges also have a truss system underneath the bridge deck to help stiffen the bridge and prevent swaying.

There are two types of suspension bridges. The more common "M" design where the cables are strung in a "M"- like fashion. The other, and the more rare design of the two, is the "A" design. In this design, two towers and four anchorages are not needed, like the "M" design, but the wires run up from the roadway to a single tower where...

Bibliography: Brain, Marshall "Howstuffworks: How Bridges Work" "Bridge Information" Bridge Types: Suspension" Placzek, Adolf K. "John Augustus Roebling - Great Buildings Online" Steinman, David Barnard "Enclyclopedia Brittanica Intermediate - BRIDGE",6101,32499,00.html "Suspension Bridge Technical Data"
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