Beam bridges

(also known as girder bridges)

Beam bridges are the simplest type of bridge, with the earliest bridges just fallen tree trunks. Single slabs of stone are also simple beam bridges and are called clam bridges.

When the river was too wide to be spanned by one stone slab, a number of slabs were used. These early stone bridges are called clapper bridges. Some of the best examples of these can be found in the granite areas of south west England. The photograph shows the clapper bridge at Wycollar, Lancashire.

Advantages:

• Good for short spans;

• Wide distances can be spanned by resting beams on piers.

Disadvantages:

• Can be expensive, even for fairly short spans, because of the need to use steel. A cheap material for beam bridges is concrete, but concrete on its own, is not strong enough to stand up to high forces of tension (pulling), so concrete needs to be reinforced with steel mesh;

• Very expensive for long spans, because of need for piers to support the long beams;

• It is not always possible to build support piers.

Bridge index.

Forces in bridges.