Bridges

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Summary Paragraph:

//**Since early times, Architecture has bring lots of ideas and solutions for human needs, bridges are one of those useful devices. Even in the most primitive human communities, the creation of bridges from simple materials is present. It took time for builders to reach a progresive improvement in the materials used to build all that up.

There are different types of bridges I would mention, but I will name briefly a couple of them, the more significants. We have for example; the simplest, the beam bridges, supported at each end by piers, sometimes made of wood and stone. After a time the arch came to stay and several kinds of bridges became popular using that technic. Romans used it in aqueducts.

Iron and Steel bridges, wich are used today, are everywhere and most of the worlds major rivers are crossed by this type. During the industrial revolution iron gained popularity as a construction material because it was stronger than stone and usually less costly. Girder bridges often carry railways and many were built in the early part of the 20th century. They are capable of carrying heavy weights. Usually they span short distances. And Suspension bridges are the cheapest way of spanning long distances, cables hold the road in position.

At the end, all types may be classified by how the forces of tension, compression, bending, torsion and shear are distributed through their structure. Most bridges will employ all of the principal forces to some degree, but only a few will predominate to keep in the running for the new generation of technics to come.**// ==== A **bridge** is a structure built to span a valley, road, body of water, or other physical obstacle, for the purpose of providing passage over the obstacle. Designs of bridges vary depending on the function of the bridge and the nature of the terrain where the bridge is constructed.==== There are six main types of bridges: beam bridges, cantilever bridges, arch bridges, suspension bridges, cable-stayed bridges and truss bridges.

//**Stone**// is very strong under compression, but it is not strong under tension. Therefore, it is not ideal for use as a beam. By contrast, //**wooden tree trunks**// or cut planks form a very strong beam when laid across a stream, despite their comparative lightness. Wood is able to carry both compression and tension equally well.
 * Beam bridges:** are horizontal beams supported at each end by piers.
 * Materials:**


 * Cantilever bridges:** are built using cantilevers—horizontal beams that are supported on only one end.

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. The Romans used the concept of the stone arch for a huge range of building applications, from doorways to vaulted roofs and from bridges to sewers. They were certainly the first civilisation to build large-scale bridges, many of which still stand today. Example; The Aqueduct Roman, above
 * Arch bridges:** are arch-shaped and have abutments at each end.

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.
 * Suspension bridges:** are suspended from cables.


 * Cable-stayed bridges:** Like suspension bridges, cable-stayed 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.

There are some materials that allows the architect to be more creative, for example; Calatrava`s bridge in Spain.
 * Truss bridges:** are composed of connected elements. They have a solid deck and a lattice of pin-jointed or gusset-joined girders for the sides.

There aren't many examples of whole bridges made of materials such as plastic - yet. The lightness brings its own problems and there are issues arising from long-term safety trials. While the possibilities opened up by these newer materials and by computer-aided design are being explored, the older staples of bridge construction are still being used – often in fresh combinations and reincarnations. These are called 'hybrid' bridge designs.
 * NEWS:**

Source: http://en.wikipedia.org/wiki/Bridge http://www.makingthemodernworld.org.uk/learning_modules/maths/02.TU.03/?section=1