The Structure Behind Bridges

General Description A bridge is a structure built to cross a valley, road, railroad track, river, body of water, or any other physical obstacle, for the purpose of providing passage over an obstacle. The designs of bridges vary depending on the function of the bridge and the nature of the terrain where the bridge is being built.

History of Bridges The Romans were the most superior bridge builders of their time. They built arch bridges and aqueducts that could stand in conditions that would damage or destroy earlier designs, some of their structures still stand today. The Alcántara Bridge in Spain is an example.

Alcántara Bridge

Types of Bridges There are six main types of bridges: Beam bridges Cantilever bridges Arch bridges Suspension bridges Cable-stayed bridges Truss bridges

Types of Bridges Beam bridges contain horizontal beams that support at each end by piers. The weight on top of the beam pushes straight down on the piers at either end of the bridge. Cantilever bridges are built using cantilevers. They are horizontal beams that only supported on one end. The largest cantilever bridge is the Quebec Bridge in Quebec, Canada.

Quebec Bridge

Types of Bridges Arch bridges are arch-shaped and have abutments at each end. The weight of the bridge is thrust into the abutments at either side. This method was first introduced by the Greeks. Suspension bridges are suspended from cables. In modern bridges, the cables hang from towers that are attached to caissons or cofferdams. The longest suspension bridge in the world is the Akashi Kaikyo Bridge (12,826 feet.)

Akashi Kaikyo Bridge

Types of 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 shorter. Truss bridges are composed of connected elements. They have a solid deck and a lattice of pin-jointed girders for the sides. They are made of metals such as wrought iron and steel or sometimes of reinforced concrete.

Truss Bridge

Similarities/Differences of a Bridge Bridges may be classified by how the forces of tension, compression, and bending are distributed through their structure. Most bridges will employ all of the principal forces to some degree, but only a few will dominate. Forces may be distributed among a large number of members, as in a truss.

Work Cited Page “Bridges” http://en.wikipedia.org/wiki/Bridge “All About Bridges” http://www.pbs.org/wgbh/buildingbig/bridge “How Bridges Work” http://www.howstuffworks.com/bridge.htm