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|
 Multispan plate girder bridge deck on concrete piers. | |
| Ancestor | Log bridge |
|---|---|
| Descendant | Box girder bridge,plate girder bridge,trestle bridge,truss bridge[citation needed] |
| 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 simplest structural forms forbridge spans supported by anabutment orpier at each end.[1] Nomoments are transferred throughout the support, hence their structural type is known assimply supported.
The simplest beam bridge could be a log (seelog bridge), awood plank, or astoneslab (seeclapper bridge) laid across a stream. Bridges designed for moderninfrastructure will usually be constructed ofsteel orreinforced concrete, or a combination of both. The concrete elements may bereinforced orprestressed. Such modern bridges includegirder,plate girder, andbox girder bridges, all types of beam bridges.
Types of construction could include having manybeams 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 beI-beams,trusses, orbox girders. They could behalf-through, or braced across the top to create athrough bridge.
Since no moments are transferred,thrust (as from anarch bridge) cannot be accommodated, leading to innovative designs, such aslenticular trusses andbow string arches, which contain thehorizontal forces within thesuperstructure.
Beam bridges are not limited to a singlespan. Someviaducts such as theFeiyunjiang Bridge in China have multiple simply supported spans held up by piers. This is opposed to viaducts usingcontinuous 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. The further apart its supports, the weaker a beam bridge gets. As a result, beam bridges rarely span more than 250 feet (80 m). This does not mean that beam bridges are not used to cross great distances; it only means that a series of beam bridges must be joined together, creating what is known as a continuous span.
| Structural types |  | |
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| Lists of bridges by type | ||
| Lists of bridges by size | ||
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