Bridge_Notes

A bridge is a structure built to span physical obstacles such as a body of water, valley, or road, for the purpose of providing passage over the obstacle. Designs of bridges vary depending on the function of the bridge, the nature of the terrain where the bridge is constructed, the material used to make it and the funds available to build it.

Briges are made With (Types of bridges):

Beam bridges are horizontal beams supported at each end by abutments, hence their structural name of // simply supported //. When there is more than one span the intermediate supports are known as piers. The earliest beam bridges were simple logs that sat across streams and similar simple structures. In modern times, beam bridges are large box steel girder bridges. Weight on top of the beam pushes straight down on the abutments at either end of the bridge. They are made up mostly of wood or metal. Beam bridges typically do not exceed 250 feet (76 m) long. The longer the bridge, the weaker.
 * Beam Bridges:**



Cantilever bridges are built using cantilevers—horizontal beams that are supported on only one end. Most cantilever bridges use a pair of continuous spans extending from opposite sides of the supporting piers, meeting at the center of the obstacle to be crossed. Cantilever bridges are constructed using much the same materials & techniques as beam bridges. The difference comes in the action of the forces through the bridge.
 * Cantilever Bridges:**



Arch bridges have abutments at each end. The earliest known arch bridges were built by the Greeks and include the Arkadiko Bridge. The weight of the bridge is thrust into the abutments at either side.
 * Arch Bridges:**



Suspension bridges are suspended from cables. The earliest suspension bridges were made of ropes or vines covered with pieces of bamboo. In modern bridges, the cables hang from towers that are attached to caissons or cofferdams. The caissons or cofferdams are implanted deep into the floor of a lake or river.
 * Suspension Bridges:**



Cable-stayed bridges, like suspension 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.
 * Cable-stayed Bridges:**



Movable bridges are designed to move out of the way of boats or other kinds of traffic, which would otherwise be too tall to fit. These are generally electrically powered.
 * Movable Bridges:**