Beam type

The four main factors are used in describing a bridge. By combining these terms one may give a general description of most bridge types:

· span (simple, continuous, cantilever),

· material (stone, concrete, metal, etc.),

· placement of the travel surface in relation to the structure (deck, pony, through),

· form (beam, arch, truss, etc.).

The three basic types of spans are shown below. Any of these spans may be constructed using beams, girders or trusses. Arch bridges are either simple or continuous. A cantilever bridge may also include a suspended span.

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Examples of the three common travel surface configurations are shown in the truss type drawings below. In a deck configuration, traffic travels on top of the main structure; in a pony configuration, traffic travels between parallel superstructures which are not cross-braced at the top; in a through configuration, traffic travels through the superstructure (usually a truss) which is cross-braced above and below the traffic.

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Simple deck beam bridges are usually metal or reinforced concrete. Other beam and girder types are constructed of metal. The end section of the two deck configuration shows the cross-bracing commonly used between beams. The pony end section shows knee braces which prevent deflection where the girders and deck meet.

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Many modern bridges use new designs developed using computer stress analysis. The rigid frame type has superstructure and substructure which are integrated. Commonly, the legs and deck are a single piece which is riveted to other sections.

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Source: http://pghbridges.com/basics.htm