Designs of bridges vary depending on the function of the bridge, the nature of the terrain where the bridge is constructed, the material used to make it and the funds available to build it. Although large Chinese bridges of wooden construction existed at the time of the Warring States, the oldest surviving stone bridge in China is the Zhaozhou Bridge, built from 595 to 605 AD during the Sui Dynasty. European segmental arch bridges date back to at least the Alconétar Bridge (approximately 2nd century AD), while the enormous Roman era Trajan's Bridge (105 AD) featured open-spandrel segmental arches in wooden construction. There are six main types of bridges: beam bridges, cantilever bridges, arch bridges, suspension bridges, cable-stayed bridges and truss bridges. The earliest known arch bridges were built by the Greeks and include the Arkadiko Bridge.
See simple suspension bridge, stressed ribbon bridge, underspanned suspension bridge, suspended-deck suspension bridge, and self-anchored suspension bridge. Cable-stayed bridges, like suspension bridges, are held up by cables. An aqueduct is a bridge that carries water, resembling a viaduct, which is a bridge that connects points of equal height.A road-rail bridge carries both road and rail traffic. A more refined measure for this exercise is to weigh the completed bridge rather than measure against a fixed quantity of materials provided and determine the multiple of this weight that the bridge can carry, a test that emphasizes economy of materials and efficient glue joints (see balsa wood bridge). A bridge can carry overhead power lines as does the Storstrøm Bridge.
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