Bridges_notes

BRIDGES
 Bridges are technological tools that aim to solve the problem of crossing an obstacle in such a way as to cut down the effort and time needed to do so. Bridges are structures that conect urban settlements,to improve the exchange of products and services.

The Beam Bridge The design is as simple as a single rigid 'beam', resting on supports at both ends. The weight of the beam, and of any traffic on it, is carried directly to the ground by the supports, often called 'piers' in the trade. They can be made out of almost any construction material. Image: A Beam Bridge The Arch Bridge The arch is really a beam curved to form a semicircular shape, which is prevented from straightening and spreading sideways by strong 'abutments' at either end. This kind of bridge can be made out of several construction materials such as brick, iron, concrete and steel. Image: An Arch Bridge The Suspension Bridge A suspension bridge is one where the road deck is suspended from cables that are strung across the river (or whatever the obstacle happens to be). There is no support in the centre of the span and the deck hangs below the supports rather than resting upon them. The first suspension bridges were just ropes hanged between two sides of the river or a gorge, with steps made of wood. Nowadays, in all modern suspension bridges, the roadway hangs from massive steel cables, which are draped over two towers and secured into solid concrete blocks, called 'anchorages', at both ends of the bridge.   Image: A Suspension Bridge  The Cable-Stayed Bridge <span style="color: #9e3131; display: block; font-family: Tahoma,Geneva,sans-serif; text-align: center;">In the cable-stayed desing, another version of the suspension bridge, the deck is hung from diagonal cables that exert a force towards the towers as well as vertically. This makes the tension in the steel cables extremely high, and hence they are very stiff. In addition, the cables effectively stabilise the towers from both sides. <span style="color: #9e3131; display: block; font-family: Tahoma,Geneva,sans-serif; text-align: center;"> <span style="font-family: Tahoma,Geneva,sans-serif; font-size: 80%;">Image: A Cable-Stayed Bridge