Cantilever bridge
A cantilever bridge is a bridge in which are parts of the structure designed as a cantilever. Large cantilever bridges have steel truss or box girder of prestressed concrete as a superstructure. In modern bridge cantilever bridges came only after the invention of the Gerber carrier in the second half of the 19th century for execution.
History
Expected boom bridges be a very old design of bridges, as can be simple versions created with stones and logs. Bridges made of these materials are still built today in Pakistan, Afghanistan, India and China for crossing rivers. These tribes with stones must be fixed on both sides that the longest possible end projects in the direction of flow. If the ends do not extend to the middle of the river, wooden structures can be placed on both sides of the above strains. In Europe, such wooden bridges are known by the Gauls. They were used in Savoy until the 18th century.
From the late Middle Ages, a proposal for a cantilever bridge made of wood from the architect Villard de Honnecourt is handed down. This construction appeared but only in the sketchbooks and appeared to have been implemented anywhere. Also this design utilizes beams, which connect the two fixed on the banks of a cantilever with one another.
Middle of the 19th century helped the engineer Heinrich Gottfried Gerber of the cantilever bridge a breakthrough. He first described in a patent of 1866, as a continuous beam can be provided with joints that he is determined statically, and is the so-called Gerber carrier. The most common design consists of two cantilever beams, the set of both banks on pillars protrude towards the middle of the river. Their ends are connected by a suspended beam that rests itself on no pillars, but is only supported by the cantilever beams.
Gerber beam were used mainly for large executed in steel truss railway bridges, which could not be implemented as a suspension bridge because of its span and higher compared to road traffic loads of the trains. After the invention of Gerber carrier yet emerged other types of steel truss cantilever bridges, but could not prevail, and were carried out in only a few buildings. Examples include the Forth Bridge, the Viaur Viaduct or the Blue Wonder.
In the 20th century a few boom bridges were only built in steel truss. In America, the construction could still last the longest, not least supported by the steel industry. Outside the Americas emerged as significant buildings, only the Howrah Bridge in India and the Minato Bridge in Japan.
The steel truss cantilever bridge was replaced mainly by prestressed concrete girder bridges, which were simpler, faster and cheaper to build. However, the technique of cantilever bridge is also used in prestressed concrete bridges for use specifically when the superstructure is built as a cantilever of each pier starting. In this design, at the end of the construction phase, the ends of each section are hingeless connected so that the superstructure to a statically indeterminate continuous beam support is.