When building a bridge, engineers must consider a number of factors. Different bridge styles distribute stresses different ways. Engineers must take the length and width of the bridge, local environmental conditions and building materials into account to decide what type of bridge to build. To know what kind of bridge is realistic for what environment, then knowing about the six main types of bridges is important. Using the wrong type can result in disaster.
Arch bridges are those that use arches as the main structural component. Basic arch bridges are differentiated from one another by the number of hinges used to allow the bridge to accommodate different loads and stresses. Some arch bridges don't include any hinges at all. Arch bridges include those where the arch is underneath the bridge, not above it, provided that the trusses are arranged vertically and not diagonally. The Hell Gate Bridge in New York is an arch bridge.
Beam bridges are very basic bridge constructions that have pieces supported on either end of the bridge. Modern bridges frequently use leg supports to distribute the load. Two main types of leg supports are used: the inclined leg, which involves a single inclined leg at each support point, and a v-leg, which uses a two-piece leg shaped like the letter "V." A haunched girder bridge is a type of beam bridge that uses flanged pieces at the extremities of the bridge. Beam bridges work much like a log overlapping the two sides of a ravine. An example of a beam bridge is the Lake Pontchartrain Causeway in southern Louisiana.
Cable-stayed bridges are one of two types preferred for longer bridges. Columns are erected with cables to support the deck of the bridge. The design is similar to a suspension bridge, but instead of the deck being curved, the deck is flat. In New York City, the East 153rd Street Bridge is a cable-stayed bridge.
Cantilevered bridges are built around horizontal structures supported on only one end. Some cantilevered bridges are very similar in appearance to arch bridges; however, they are supported by diagonal bracing rather than vertical bracing. These types of cantilevered bridges are known as spandrel braced. The other type of cantilevered bridge is the cantilever through truss formation, where trusses are either above the bridge or both above and below. An example of a cantilevered bridge is the Queensboro Bridge.
The suspension design is the other design for very long bridges. Here pylons or towers are erected and wires hold the deck of the bridge in place on the deck's underside. The Brooklyn Bridge is a famous suspension bridge.
The truss bridge is a simple bridge design that includes most covered bridges. Two types of uncovered truss bridges are used: the king post, which has two diagonal posts supported by a single vertical post in the center, and the queen post. which has two diagonal posts, two vertical posts and a horizontal piece which connects the two vertical posts at the top. New York's Kosciuszco Bridge is a truss bridge.
- Bridge image by Hedgehog from Fotolia.com