The arch is one of the older forms of bridge used in many Roman structures. It is like an inverted suspension bridge, with all the tensions replaced by compressions, and vice versa. The other great difference is in the stability of the system. You can drive heavy weight across an arch and cause it to flex, and it will always return to its original position, after movement.

The girder bridge is made up of two or more large beams that can stretch across the length of the obstacle that it is built to overcome. Many cantilevers that pivot as the load on the bridge shifts are used to even out the stress on th

e entire structure. This is the most basic and most widely used design (Krinsiuns III).

Almost all of the bridges from the past have been made of concrete and steel neither of which have good principals against stress and the elements. On average it takes twenty years for a concrete bridge to decompose and become brittle, therefore making it useless. The concrete and steel bridges must be maintained constantly and are always depleting. If we used modern composite materials such as carbon fiber our bridges would no break down because of the weather and would be much stronger than concrete-steel bridges because we would be able to construct shape that are perfectly solid and structurally sound. In a test by the US Army composite materials prove to be superior to concrete bridges in many ways. It took a 1200 pound composite beam to hold the weight that it took a 6300 concrete-steel beam to hold. The concrete beam began to crumble under the stress where as

Some common words found in the essay are:
Krinsiuns III, , Composite II, suspension bridge, II Examples, composite materials, IV Conclusion, modern technology, box girder, composite beam, anchorages ground, bridges built, concrete steel, girder bridge, beam hold,
Approximate Word count = 647
Approximate Pages = 3 (250 words per page double spaced)