Bridges

A bridge is a structure designed to carry pedestrians or vehicles across such obstacles as ravines, rivers, or other roads or railroads. In all three types of bridge--beam, arch, and suspension--the foundations must carry the full weight of the bridge and the traffic on it. The vital differences, however, are that arched bridges are in compression and thrust outward on their end supports or bearings, whereas the cables of a suspension bridge are in tension …

…The newest bridge design, the cable-stayed bridge, is suspended by cables that run directly down to the roadway from centrally-positioned towers. Because they are less costly than conventional suspension bridges, cable-stayed bridges have been built, largely in Europe, for spans up to about 700 m (2,000 ft). The dynamics of these bridges, however, create special stresses on the cables, and improved technologies must be used to prevent cable corrosion. Html://www.bridgedesigns.com/bridges/history/info.html