Beam bridge

Beam bridge

Multispan plate girder bridge deck on concrete piers. Multispan plate girder bridge deck on concrete piers.
Ancestor	Log bridge[1]
Related	None
Descendant	Box girder bridge, Plate girder bridge, trestle, truss bridge
Carries	Pedestrians, automobiles, trucks, light rail, heavy rail
Span range	Short
Material	Timber, iron, steel, reinforced concrete, prestressed concrete
Movable	No
Design effort	Low
Falsework required	No unless cast-in place reinforced concrete is used

Beam bridges are the most simple of structural forms being supported by an abutment at each end of the deck. No moments are transferred throughout the support hence their structural type is known as simply supported.

The simplest beam bridge could be a slab of stone, or a plank of wood laid across a stream. Bridges designed for modern infrastructure will usually be constructed of steel or reinforced concrete, or a combination of both. The concrete used can either be reinforced, prestressed or post-tensioned.

Types of construction could include having many beams side by side with a deck across the top of them, to a main beam either side supporting a deck between them. The main beams could be I-beams, trusses, or box girders. They could be half-through, or braced across the top to create a through bridge.

Because no moments are transferred, thrust, as from an arch bridge, cannot be accommodated, so leading to innovative designs, such as lenticular trusses & bow string arches, which contain the horizontal forces within the superstructure.

Beam bridges are not limited to a single span. Some viaducts such as the Feiyunjiang Bridge in China have multiple simply supported spans supported by piers. This is opposed to viaducts using continuous spans over the piers.

Beam bridges are often only used for relatively short distances because, unlike truss bridges, they have no built in supports. The only supports are provided by piers.