There are over 500,000 bridges in America alone, according to a PBS.org's "Bridge Basics." Bridges provide a means of transportation both for daily commutes and for product distribution. Although bridges have been built since ancient times, modern advancements have allowed for new innovations and designs.
An arch bridge uses simple natural forces for support and can be about 800 feet to 1,000 feet in length. The bridge consists of two supports that meet in the middle to form an arch-shaped bridge. Arch bridges date to ancient times, when the Romans made them out of stone. Now they are normally composed of concrete or steel. West Virginia's New River Gorge Bridge is an example of an arch bridge. It is composed of steel and spans over 4,000 feet in length.
Beam bridges are seen over smaller bodies of water and usually do not span more than 250 feet. This is because of the nature of its construction. PBS.org's "Bridge Basics" defines a beam bridge as "a horizontal beam supported at each end by piers." The farther apart the piers are from one another, the more fragile the bridge will be. Beam bridges can be combined to form a long link of bridges, known as a continuous beam bridge. The Chesapeake Bay Bridge in Virginia is one example of a continuous beam bridge. It spans 79,200 feet and is made of steel and concrete. Drawbridges are also classified as beam bridges.
Truss bridges are easily recognized by their triangle patterns, also known as trusses. A truss bridge is basically a beam bridge with supporting beams. The bridges can span for longer distances than basic beam bridges because of their support trusses, which provide support for the central part of the bridge. They are commonly used in railroad tracks or over streams and rivers.
Suspension bridges combine truss supports and cables to provide stability and support for long bridges. The cables are draped between two towers on either side of the bridge, and a truss system is used underneath the road to provide even more support. Suspension bridges can span at least 7,000 feet in length. Examples of suspension bridges include the Golden Gate Bridge, Brooklyn Bridge and the Akashi Kaikyo Bridge in Japan.
Cable-stayed bridges are similar to suspension bridges insofar as both use cables and towers to support the bridges. However, rather than draping the weight of the cables between the towers, cable-stayed bridges function by extending the cables to the bridge itself. As illustrated by NOVA.com, the cables "transfer the load of the bridge to the tower." Examples of cable-stayed bridges include Tampa Bay's Sunshine Skyway and China's Sutong Bridge.