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Bridge is not a construction but it is a concept, the concept of crossing over large spans of land or huge masses of water, and to connect two far-off points, eventually reducing the distance between them. The bridge provides passage over the obstacle of small caverns, a valley, road, body of water, or other physical obstacle. Designs of bridges vary depending on the nature of the terrain and the function of the bridge and where it is constructed. The Oxford English Dictionary traces the origin of the word bridge to an Old English word brycg, of the same meaning, derived from German root brugj?.
The first bridges were believed to be made by nature — as simple as a log fallen across a stream. The first bridges made by humans were probably spans of wooden logs or planks and eventually stones, using a simple support and crossbeam arrangement.
The Indian Epic literature Ramayana provides mythological accounts of bridges constructed from India to Sri Lanka by the army of Sri Rama, the mythological King of Ayodhya.
The recent satellite photograph depicts the existence of this bridge, referred to in Ramayana.
Mention of bridges being constructed by Mauryan dynasty in India, is given in Kautilya’s “Arthasastra”. During the wars Mughals have constructed many bridges across major rivers, in India.
Before pre-historic people began to build the crudest shelter for themselves they bridged streams. Trees that have fallen across the stream from bank to bank acted as bridges. The wandering tribe that first deliberately made a tree fall across a stream were the first bridge builders.
Observing monkeys swing of the several vines, led to connecting parallel cables with some sort of cross pieces, to support as bridges. Later hand grips were proved which led to suspension bridges.
Rope bridges, a simple type of suspension bridge, were used by the Inca civilization in the Andes Mountains of South America
The first bridges were natural of huge rock arch that spans. The first man-made bridges were tree trunks laid across streams in girder fashion, flat stones, and festoons of vegetation, twisted or braided and hung in suspension.
These three types - beam, arch, and suspension - have been known and built since ancient times and are the origins from which engineers and builders derived various combinations such as the truss, cantilever, cable-stayed, tied-arch, and moveable spans
Chinese built big bridges of wooden construction, and later stone bridges, and the oldest surviving stone bridge in China is the Zhaozhou Bridge built around 605 AD during the Sui Dynasty.
This bridge is also historically significant as it is the world's oldest open- stone segmental arch bridge.
The ancient Romans were the greatest bridge builders of antiquity.
They used cement, - called pozzolana consisting of water, lime, sand, and volcanic rock, which reduced the variation of strength found in natural stone.
Though extremely versatile, wood has one obvious disadvantage and during the 18th century there were many innovations in the design and a major breakthrough in bridge technology came with the erection of the Iron Bridge in Coalbrookdale in England during 1779, using cast iron for the first time as arches to cross the river Severn.
With the Industrial Revolution, steel, which has a high tensile strength, replaced wrought iron for the construction of larger bridges to support large loads, and later welded structural bridges of various designs were constructed.
Bridges are classified as Beam bridges, Cantilever bridges, Arch bridges, Suspension bridges, Cable stayed bridges and Truss bridges.
- Beam Bridge: 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.
- Cantilever bridges are built using cantilevers—horizontal beams that are supported on only one end. Most cantilever bridges use two cantilever arms extending from opposite sides of the obstacle to be crossed, meeting at the center.
- The Arch Bridge 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.
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The suspension bridge 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.
- The Cable-stayed Bridges like suspension bridges are held up by cables. However, in a cable-stayed bridge, less cable is required and the towers holding the cables are proportionately shorter. The longest cable-stayed bridge is the Sutong bridge over the Yangtze River in China.
- Truss bridges are composed of connected straight elements with the help of pin joints. They have a solid deck and a lattice of pin-jointed or gusset-joined girders for the sides. Early truss bridges were made of wood, and later of wood with iron tensile rods, but modern truss bridges are made completely of metals such as wrought iron and steel or sometimes of reinforced concrete.
- Cable-stayed bridge is a bridge that consists of one or more columns - towers or pylons, with cables supporting the bridge deck.
Build a Bridge. After visiting several bridges in your country and browsing the websites looking at different designs, try to make a model bridge. First, draw out the design. Then select your material(s). Builders often use balsa wood, other types of wood, strings, toothpicks, straws and even alu foil. It is fun constructing your own bridge model of your imagination and design. If need be you can colour your model.
Some of the famous bridges around the world:
George Washington Bridge
Howrah Bridge, Kolkata
