Railroad Bridge

a structure that carries a railroad line across some obstacle (such as a watercourse or ravine). Rail-road bridges are subjected to intensive dynamic effects: great demands are made on their strength, durability, and stability in order to ensure safe and uninterrupted railroad traffic and provide for long-range increases in railroad traffic. Continuous truss bridges are usually used to cross the navigable channels of large rivers. For nonnavigable streams and small rivers, steel beams or spanning beams made of prestressed reinforced concrete are used.

Steel spans made up of welded elements and sections held together by highly resistant friction bolts are widespread in modern railroad bridges, as are continuous steel beams that function as a unit with the reinforced-concrete slab underlying the roadbed. Arch-type reinforced-concrete railroad bridges are less common. Wooden railroad bridges, which are less durable, may be used only on railroads of the third category.