桥梁

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桥梁(bridge)

水平搭造的结构，以利行人或交通工具跨越通道的空处。桥梁的结构总是向世人展现它最伟大的挑战性。最简单的桥梁是板梁桥，由架在跨距两端的刚性直梁组成（如横放在溪流上的木干）。古罗马的桥梁以圆拱形着名，比石板梁桥拥有更长的跨距，也比木桥更为耐久。拱桥的改进形式是开合桥（吊桥），是在中世纪发展出来的。升降桥是另一种可移动的桥梁，可改变位置让船只通过。悬索桥（如布鲁克林桥、金门大桥）跨越更大的距离，主要的支撑力量来自缆索，缆索由数千束铁丝组成，固定在两端的高塔和锚桩上，桥面是由固定在主索上的垂直缆索支撑。另外一些类型的桥梁包括桁架桥，是最普遍的桥梁（如铁路桥梁），因为它只需用少量的材料来承受大的载力；悬臂桥，典型上有三个跨距，外面两边的跨距锚固在岸边，中央的跨距则靠悬臂梁支撑。

English version：

bridge

Structure that spans horizontally to allow pedestrians and vehicles to cross a void. Bridge construction has always presented civil engineering with its greatest challenges. The simplest bridge is the beam (or girder) bridge, consisting of straight, rigid beams placed across a span (e.g., a tree trunk laid across a stream). Ancient Roman bridges are famous for their rounded arch form, which permitted spans much longer than those of stone beams and were more durable than wood. A modification of the arch bridge was the drawbridge, developed during medieval times. The lift bridge, another movable type, can change position to allow clearance for ships and boats. Suspension bridges (e.g., Brooklyn Bridge, Golden Gate Bridge) are capable of spanning great distances; their main support members are cables composed of thousands of strands of wire supported by two towers and anchored at each end, and the roadway is supported by vertical cables hung from the main cables. Other bridges include the truss bridge, popular (e.g., for railroad bridges) because it uses a relatively small amount of material to carry large loads, and the cantilever bridge, typically made with three spans, with the outer spans anchored down at the shore and the central span resting on the cantilevered arms.

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