桥梁结构说明.doc

Bridge Design and Construction
Planning. The first step leading to the construction of a modern major bridge is prehensive study to determine whether a bridge is needed. If it is to be a highway bridge, in the United States for example, a planning study is initiated by a state bridge authority, possibly in cooperation with local governments or the federal government. Studies are made to estimate the amount of bridge traffic, the relief of aimed traffic in nearby works, the effects on the regional economy studied, and the cost of the bridge. The means for financing the project, such as public taxes or sale of revenue bonds repaid by toll charges, are considered. If the studies lead to a decision to go ahead with the project, the land needed for the bridge and its approaches is acquired at the selected site. At this point, field engineering work is started, Accurate land surveys are made. Tides, flood conditions, currents, and other characteristics of the waterway are carefully studied, Boring samples of soil and rock are taken at possible foundation locations, both on land and under the water.
Selection of bridge design. The chief factors in deciding whether a bridge will be built as a girder, cantilever, truss, arch, suspension, of some other type are : (1) location; for example, across a river; (2) purposes; for example, a bridge for carrying motor vehicles; (3) span length