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Topic – Four Types of Bridges

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Four Types of Bridges

In the diagrams below, the pairs of arrows show the following forces at work:

<- -> tension           -> <- compression

Beam Bridge

A beam bridge has a horizontal beam supported by two piers. The beam bends when a load is on the bridge. A load can be cars, trucks, or a train. Compression acts on the top side of the beam and the two piers. Tension acts on the bottom side of the beam.

Arch Bridge

The arch is a very strong shape. A load on top of the bridge causes compression on the top of the arch. It also causes tension at the bottom of the arch. This tension could cause the arch to spread apart, making it weaker. The material on the sides of the arch acts like buttresses. The material keeps the arch from spreading apart.

Truss Bridge

A truss bridge is built with triangles made of steel bars.
A triangle is a very strong shape. Compression and tension forces act on the bridge. The diagram below shows the forces.

Suspension Bridge

On a suspension bridge, tall towers support the main cable. Smaller cables attached to the main cable support the roadway. These cables are called suspenders. The main cable is attached to large blocks at each end of the bridge. The load of traffic on the bridge is transferred to the suspenders. This causes tension in the suspenders. The suspenders transfer the load to the main cable. This causes tension in the cables. Compression acts on the towers as they support the weight of the bridge and the traffic.


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