Types of Bridges

Bridge is not a construction but it is a concept, the concept of crossing over large spans of land or huge masses of water. The idea behind a bridge is to connect two far-off points eventually reducing the distance between them. Apart from this poetic aspect of ‘bridges’, there is a technical aspect to them that classifies bridges on the basis of the techniques of their construction.

The different types of bridges are:
Beam Bridge: A beam bridge was derived from the log bridge. It is built from shallow steel beams, box girders and concrete. Highway overpasses, flyovers or walkways are often beam bridges. A horizontal beam supported at its ends comprises the structure of a beam bridge. The construction of a beam bridge is the simplest of all the types of bridges.

Truss Bridge: A truss bridge is built by connecting straight elements with the help of pin joints. Owing to the abundance of wood in the United States, truss bridges of the olden times used timbers for compression and iron rods for bearing tension. Truss bridges came to be commonly constructed from the 1870s to the 1930s. Deck truss railroad bridge that extends over the Erie Canal is one of the many famous truss bridges.

Arch Bridge: Going by its name, it is arch-shaped and has supports at both its ends. The weight of an arch-shaped bridge is forced into the supports at either end. The Mycenaean Arkadiko Bridge in Greece of 1300 BC is the oldest existing arch-shaped bridge. Etruscans and the ancient Greeks were aware of arches since long. But the Romans were foremost in discovering the use of arches in the construction of bridges. Arch bridges have now evolved into compression arch suspended-deck bridge enabling the use of light and strongly tensile materials in their construction.

Suspension Bridge: A bridge falling under this category is suspended from cables. The suspension cables are anchored at each end of the bridge. The load that the bridge bears converts into the tension in the cables. These cables stretch beyond the pillars up to the dock-level supports further to the anchors in the ground. The Golden Gate Bridge of USA, Tsing Ma Bridge of China and the Humber Bridge of England are some of the famous suspension bridges.

Cable-stayed Bridge: Structured similar to the suspension bridges, the difference lies in the amount of cable used. Less cable is required and consequently, the towers holding the cables are shorter. Two variants of cable-stayed bridges exist. In the harp design, cables are attached to multiple points of the tower thus making them parallel. In the fan variant of design, all the cables connect to the tower or pass over it. Cable Bridge boasts of being the first cable-stayed bridge of USA. Centennial Bridge is another well-known cable-stayed bridge.

Cantilever bridge: Cantilevers are the structures that project along the X-axis in space. They are supported only on one end. Bridges intended to carry lesser traffic may use simple beams while those aimed at handling larger traffic make use of trusses or box girders. The 1800 feet Quebec Bridge of Canada and the San Francisco-Oakland Bay Bridge that is 1400 feet long are some examples of the cantilever bridges.

Man’s desire to reach the ‘unreachable’ and his desire to venture new places led him to construct bridges that helped him overcome physical obstacles. A log of wood floating on water might have inspired man to build bridges for the very first time. Human intellect applied technology to construct bridges that spanned great distances. The seemingly unreachable destinations thus came within the reach of man!