The earliest constructed bridge still standing today is the Arkadiko Bridge (Top Right) in Greece. It was constructed in the 13th century BC to allow chariots to cross a ravine. It is comprised of several large stones stacked together to form an arch. Arch bridges were the most common form of bridge constructed by ancient civilizations, but there were exceptions. Civilizations in India were known for constructing bridges using bamboo. Ancient Chinese engineers constructed wooden bridges. The Inca frequently constructed primitive suspension bridges using ropes.
The use of iron and steel allowed for the construction of much larger and stronger bridges. Today, some types of bridges constructed include beam, cantilever, truss, arch, suspension, and cable-stayed. Beam bridges are composed of horizontal beams supported by structures at each end, and occasionally have additional support structures in the middle. Cantilever bridges are similar to beam bridges, but are only supported by cantilevers on each end of the bridge. Truss bridges are supported by connected sections forming triangular units. Arch bridges are constructed in an arch, which allows the weight of the bridge to be transferred to abutments on the ends of the bridge. Suspension bridges are supported by cables in tension, which are connected the bridge deck to large support towers. Cable-stayed bridges are similar to suspension bridges, but use fewer cables and taller support structures. |