土木工程外文翻譯(文件)
【正文】 ers used a predesigned tabulated set of bridge ponents, where the superstructure and the substructure ponents are selected based on certain global characteristics and dimensions of the bridge such as, height of the columns, roadway width, bent skewness and span length. The predesigned bridges always hold the same assumptions in terms of material strength. Then, modification to footings or other ponents might be introduced based on site Conditions.The superstructure of these bridges consist of prestressed concrete girders that are supported by concrete bents, which usually consist of a cap beam that is 3ft x ft ( x m) supported by a number of circular columns, typically 3 ft ( m). The number of the columns depends on the bridge skewness and the roadway width. Spread footings or footings on timber piles were the mon footing systems used.The MSSS prestressed concrete bridges built in Washington State in the 1960’s were designed with little or no attention to seismic forces. Seismic provisions that guarantee appropriate ductility and acceptable seismic performance such as confinement, rebar splice length and girder seatlength were not considered. Only couple of girder stops where used tosupport the bridge deck against accidental lateral movement. Longitudinal restrainers were not monly provided, as the contact length between the girders and the top of the cap beam was assumed to be sufficient to acmodate longitudinal displacement. Abutments were typically seattype supported on strip footing or timber piles. Recently, Washington State Department of Transportation (WSDOT) has menced a prehensive seismic analysis program to evaluate the vulnerability of the exiting bridges under a seismic event and to determine the most effective retrofit alternative. The Bridge investigated in this study is one of the representative MSSS prestressed bridges built in WA. The bridge was built in the 1960’s and widened twice from its both sides, in 1979 and 2001. Apparently, the last widening was co
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