Last Post 24 Sep 2014 11:58 PM by James Shepard. 0 Replies.
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James Shepard
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24 Sep 2014 11:58 PM
    To build bridge piers, workers need a water-free environment to excavate or dig the foundations. This is achieved by using a caisson, a hollow, water-tight structure made of concrete, steel, or other material that can be sunk into the ground. When building a bridge over a river, workers sink a caisson filled with compressed air into the river until it reaches the river bottom. The workers then go into the caisson and dig out soil from the riverbed until they come to bedrock. The caisson, which has sharp bottom edges, continually moves downward during the digging until it comes to rest on bedrock. Concrete is then poured into the caisson to form the lowest section of the new bridge pier.

    Trusses. The strength of a cantilever bridge (or any bridge) can be increased by the use of trusses. A truss is structure that consists of a number of triangles joined to each other. The triangle is an important component of many kinds of structures because it is the only geometric figure that cannot be pulled or pushed out of shape without changing the length of one of its sides. The cantilever beam, end beams, and joining beams in a cantilever bridge are often strengthened by adding trusses to them. The trusses act somewhat like an extra panel of iron or steel, adding strength to the bridge with relatively little additional weight. The open structure of a truss also allows the wind to blow through them, preventing additional stress on the bridge from this force.

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