Bridge types

Bridges carry roads, railways, pipes or people over obstacles, and their form follows the span, the loads, the ground and the way they will be built.

Beam and slab bridges are the most common for short and medium spans: precast or cast-in-place girders, often prestressed, carrying a deck. Box girders, built segment by segment, reach further and resist twisting, which suits curved viaducts and metro lines. Arch bridges carry load in compression to strong abutments. Truss bridges use triangulated steel members, long familiar on Indian railways.

For longer spans, cable-stayed bridges hang the deck from towers with straight cables, and suspension bridges hang it from main cables draped over towers and anchored at the ends.

Movable bridges, such as vertical-lift spans, let ships pass. Whatever the type, every bridge needs foundations matched to the river or ground, bearings and expansion joints that let the deck move with temperature, and drainage and protection for a long life.