The Structure Behind Bridges

1. The Structure Behind Bridges

2. 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.

3. History of Bridges • The Romans were the most superior bridge builders of their time. • They built arch bridges and aqueductsthat 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.

4. Alcántara Bridge

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

6. 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.

7. Quebec Bridge

8. 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 bridgesare 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.)

9. Akashi Kaikyo Bridge

10. 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.

11. Truss Bridge

12. 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.

13. 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