A beam bridge is a superstructure supported by prestressed girders or steel beam, the weight of which is carried by the substructure—piers and abutments underneath.
Bridges designed for modern infrastructure will usually be constructed of steel or reinforced concrete or a combination of both. The concrete beams are always reinforced and may be prestressed or post stressed.
Beam bridges are typically used for relatively short distances because they lack built-in supports. The only support is provided by piers. The farther apart the piers, the weaker the bridge. As a result, a single-span rarely extends more than 180 feet. When beam bridges are constructed to span longer distances, a series of beams is joined together, creating what can be called a multi-span structure.
