《关于桥梁的英语简介》的译文

[外文原文]

Bridge Introduction

The simplest type of span is a beam bridge, consisting of a rigid beam between two supports. Today most simple beam bridges are strengthened by a truss, which is based on the triangle. Diagonal beams that extend between the horizontal and vertical beams give support against both compression and tension. Many early truss bridges were built of wood; one that was erected across the Susquehanna River in Pennsylvania in 1815 had a span of 110 meters. Iron and then steel were later used in the construction of truss bridges, still further increasing their strength. Trusses are not only strong but also light, because all unnecessary materials have been eliminated in their designs.

Another type of beam bridge is the cantilever, in which a horizontal beam extends beyond its support. Cantilever bridges, like trusses, had also been built before iron and steel became available. Most cantilever bridges have two arms of truss structure t