Types+of+Bridges

There are many types of bridges. Three of the main types of bridges include; beam, arch, and suspension bridges. Each bridge is built and given support in different ways. The best way to tell what kind of bridge it is by looking at where the support is. A bridge is a way of providing easy ways of getting over difficult obstacles.
 * Types of Bridges **

Beam Bridges

Beam bridges are the least complex and least expensive of structural forms. A beam bridge has a horizontal beam that is supported by an abutment at each end of the bridge deck. The beam of the bridge has to be strong so that it will not bend under its own weight and the weight of traffic that goes over the bridge. When the beam is pushed on by a load, the beam’s top edge is compressed, or pushed together, and the bottom edge is stretched, which creates tension. The most simple beam bridge could be a slab of rock or a piece of wood placed over a small river. Beam bridges carry people, cars, trucks, light and heavy trains. They are made of from wood, iron, steel, reinforced and pre-stressed concrete. Beam bridges are not moveable and their design effort is low. There are three types of beam bridges. One of the types is a cantilever bridge. A cantilever bridge is made from two beams or trusses. They are put together in the center by a connecting member and are held up by piers that are pulled down by balancing members.Another type of beam bridge is a truss bridge, which is pretty much a fancy beam bridge. The truss is a triangle design that is used for support to hold more weight and span larger distances, supports span across the top sides of the bridge some trusses are part of the underneath of the bridge. Truss bridges use small amounts of material to support big weights. The last type of beam bridge is a draw bridge. Draw bridges are used to go over a water source. They can raise or open in the middle. Draw bridges rise so that big ships can go through them. An example of a beam bridge is the Bridgeport Bridge in Lawrence County, Illinois (below).

Suspension Bridges



A suspension bridge is a type of bridge in which the deck is hung below suspension cables on vertical suspenders.The earliest suspension bridges were ropes thrown across an obstacle, with a deck possibly at the same level or hung below the ropes. Suspension bridges have the cables anchored in the ground at either end of the bridge. Any load applied to the bridge is transformed into a tension in the main cables. The main forces in a suspension bridge of any type are tension in the cables and compression in the pillars. There are many different types of suspension bridges. Some are: simple suspension bridge, under spanned suspension bridge, stressed ribbon bridge, self-anchored suspension bridge. A simple suspension bridge is supported entirely from anchors at either end, and has no towers or piers. The under spanned suspension bridge is a rare suspension bridge where the deck is raised on posts above the main cables. A stressed ribbon bridge is a tension structure where suspension cables are embedded in the deck. And the self-anchored suspension bridge is a suspension bridge in which the main cables attach to the ends of the deck. The first suspension bridge actually built was in 1801 by American engineer and inventor James Finley at Jacob’s Creek, in Westmoreland County, Pennsylvania.The longest suspension bridge is the Akashi Kaikyo Bridge. It is located in Kobe-Awaji Route,Japan. The main span is 6,532 ft.



Arch Bridges

An arch bridge is a bridge with abutments at each end shaped as a curved arch. An abutment is a structure built to support the lateral pressure of an arch or span, e.g., at the ends of a bridge supports. They carry the load and keep the ends of the bridge from spreading out. The load is supported from the sides of the bridge. The load is carried outward along the curve. Arch bridges were originally built for stone and brick. Now and days they are made of reinforced concrete, steel, or iron. Arch bridges are one of the oldest types of bridges. Arch bridges are one of the most used bridges now. Arch bridges have great natural strength. An arch is curved upward against opposing forces. The abutments at the end of the bridge keep the bridge from moving apart and transfer the force of the load to the ground. Arch bridges are still used today. An example of an arch bridge is the Rainbow Arch Bridge in Riverton, Kansas. (below)



Conclusion

In conclusion, bridges help us with so many tasks. Without them we would not have a easy way of getting over obstacles. Bridges help us everyday. Beam, suspension, and arch bridges are the three main types of bridges. When bridges are built, the type of bridge is considered based on the obstacle that is being over come. So next time you cross a bridge, think of how hard it would have been to pass through without these wonderful structures.

__Work Cited:__ Beam Bridge Facts: [] [|Beam bridge - Wikipedia, the free encyclopedia] []  []

Beam Bridge Picture: []

Arch bridge facts: http://science.howstuffworks.com/engineering/civil/bridge5.htm http://en.wikipedia.org/wiki/Arch_bridge [] [] [] [] [] []
 * []
 * []
 * []

Arch bridge picture: http://www.users.globalnet.co.uk/~msmith03/route66/R66_Kansas1.htm

Suspension Bridges [] [] [] [] [] [] []