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Why is a beam bridge strong?
A beam bridge is the simplest kind of bridge. In the past they may have taken the form of a log across a stream but today they are more familiar as large box steel girder bridges.
A beam bridge needs to be stiff. It needs to resist twisting and bending under weight.
A beam bridge is made of a horizontal beam that is supported at each end by piers. The weight of the beam pushes straight down on the piers.
How a beam bridge works
Under load, the beam’s top surface is pushed down or compressed while the bottom edge is stretched or placed under tension. If we imagine that there is an imaginary line running down the centre of the beam this line remains at its original length while the material above is compressed and the material below is stretched.
When might you build a beam bridge?
Beams bridges are often used for short distance over the stream. The only supports are the piers. If the distance is too long, the bridge is weaker. If the beam bridges are used for the great distance, the people have to use a series of beam bridges joined together.
Some Beam Bridges
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