Box girder bridge

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Box girder bridge
Concrete box girder bridge (double with common deck)
Ancestor	Beam bridge
Related	Tubular bridge, plate girder bridge, jetway, skyway
Descendant	Cable stayed bridge, segmental bridge, viaduct
Carries	Pedestrians, automobiles, trucks, light rail, heavy rail
Span range	Short
Material	Iron, steel, reinforced concrete, post-stressed concrete
Movable	No
Design effort	Medium
Falsework required	Yes, for cast-in place reinforced or post-stressed concrete is used, which is typical for freeway overpasses

A box girder bridge is a bridge commonly used for roadway flyovers and for modern elevated structures of light rail transport. They may be fabricated from post-stressed concrete or sheet steel plate. If of concrete, they may be cast in place using falsework supports, removed after completion, or may be prefabricated (as is usually the steel plate type) in a fabrication yard, then transported and emplaced using cranes. The latter method is often used in situation where access for construction is limited to times of light traffic, which may be detoured around the work area using only a limited number of lanes.

Single box girder bridge (concrete), Australia. A similar bridge on this river was fabricated ashore and pushed across its pylons

Single box girder bridge (steel), flyover above eastern approach of the San Francisco-Oakland Bay Bridge. The traffic could only be rerouted for a few hours during the night, so this entire segment was prefabricated nearby, brought in on specialized trucks, and placed on its pylons using large cranes. Note numerous bolts used to fasten the segments together, required as this is designed to survive a nearby 8.5 magnitude earthquake without damage and it is also founded upon poor quality soils that tend to induce intense ground motion

Erskine Bridge, near Glasgow.