Remember singing “London Bridge is falling down ...” in school and at home during those growing up years? One of the most loved nursery rhymes; it is also related to one of the most symbolic English monuments of all times, the London Tower Bridge. Bridges have always been enchanting structures. Creating bridges across vast expanses of water have always been a challenge and an achievement. So, be it the Golden Gate Bridge in San Francisco or the Sydney Harbor Bridge in Sydney, bridges were, are and will be the landmarks of the cities. Each great bridge is distinct in its features and thus a marvel in itself. The basic structure fro the bridge is always based on a few principle factors such as the type of support provided, length of the bridge, proximity to natural disaster zones and of course, the cost. Herein we have described the most common types of bridges.
Different Kinds Of Bridges
The simplest types of all bridges, beam bridges are recognized by horizontal beams, supported by two piers at the end. They are the earliest type of bridges. Example of an oldest beam bridge would be a sight, wherein you come across logs of wood kept across a narrow stream, serving as a pathway. Beam bridges normally do not exceed 250 ft in length. The longest beam bridge is Lake Pontchartrain Causeway in the United States, with a total length of 38.35 km. It is made of parts with individual span of 17 m each.
These bridges are supported as cantilever beams. Cantilever beams are supported on one side only, with the other end being usually free. Most bridges of this kind have two cantilever arms coming from opposite ends and meeting at the center. The largest cantilever bridge is the 549-metre long Quebec Bridge in Canada.
Bridges which are arch-shaped fall in this category. They possess abutments on each end, which support the weight of the bridge on them. They are known to exist from a long time. Ancient Greeks have been known to use them. The Sheikh Rashid bin Saeed Crossing in Dubai, scheduled for completion in 2012, will be the longest arch-bridge in the world, once completed
These bridges are suspended from cables, which support the weight of bridge in a webbed form. The earliest suspension bridges were made of ropes or vines covered with pieces of bamboo. In modern days, suspension bridges are suspended using cables hanging from towers supported on caissons or cofferdams. The nearly 4km long, Akashi Kaikyo Bridge in Japan is the longest suspension bridge in the world.
Though similar to suspension bridges, in a cable-stayed bridge, less cable is required and the towers holding the cables are proportionately shorter. They are never as big as the suspension bridges. The longest cable-stayed bridge is the Sutong Bridge over the Yangtze River in China.
These bridges are made of connected elements, which may be stressed by tension, compression or both. The condition of stress depends on the dynamic load on the bridge. A Truss bridge is more economical in construction than any other type due to its efficient use of materials. They have a solid deck and a lattice of pin-jointed or gusset-joined girders for the sides. The world’s largest truss bridge is also the world’s largest cantilever bridge, i.e. The Quebec Bridge.