Bridges are built with cables, girders, arches and reinforced steel and concrete to channel the weight of the bridge onto abutments at either end of the structure and piers along the span of the bridge that rest on concrete pilings driven into the land or water beneath them. Types of bridges include, suspension, arch and cablestayed.
In addition to spanning distances, such as rivers, bays and canyons, bridges distribute the loads that they contain by compression, or pushing forces, and tension, or pulling forces.
An arch bridge is built using compression. It pushes its load outward and is made strong when load is added as the materials of the arch compress together with added weight. It spreads the load horizontally and vertically into the ground beneath.
A suspension bridge uses tension spread between many small cables that are in turn supported by thicker cables that are stretched between vertical piers above the bridge. The surface of the bridge is reinforced by trusses and girders underneath but is supported or hung by the cables above.
A cable-stayed bridge is similar to a suspension bridge in that it uses cables from above and tension to support it. The difference lies in the fact that the cables in the cable-stay bridge are attached directly to the piers instead of having cables stretched between them.