Why Do People Use Arch Bridges

A structure that is used by people and vehicles to cross areas that are normally obstacles to travel is called a bridge. Engineers design and build bridges over railroad tracks, busy highways, canyons, and lakes. Without bridges, people would need boats to cross waterways and would have to travel around such obstacles as canyons and ravines.

The first bridge was made by nature and was a dead tree over a stream or river. The first man made bridge was an arch bridge made around the time 2200 B.C. and was built by the ancient Babylonians. Arch bridges were also built by the ancient Chinese, Egyptians, Greeks, and Romans using bricks, and stones. Excluding the natural occurring and arch bridges there are six other main types that are used

Bridges are supported by beams that have been buried into the ground. The supports that are dug into the end of the bridge are called abutments. Piers are the support(s) in between the abutments. Bridges that only have abutments are single-span bridges, while ones with piers are called multi-spanned bridges. Regularly the longer bridges are multi-spanned. The longest span of a bridge is called the main span. The bridge with triangles on it is called a truss bridge. The individual pieces of the triangle are called trusses. A truss bridge’s main span can extend up to 1,000 feet (300 meters). The triangle on every truss is made of steel or wood. A girder bridge is made up of girders which are beams that the end rests on piers or abutments. They can be used to cross most areas. The longest span of a girder bridge is 1,000 feet(300 meters) which is the same as a truss bridge. The two main types of girder bridges are box girder and the plate girder. The one that looks like a long box that lies between the piers or abutments is the box girder. Box girders are made of steel or concrete. The plate girder looks like a T or an I if you look at the end of the beam. It supports the bridge on two