A beam bridge is the most common type of bridge and is most often found on local roads. It is a rigid horizontal structure that rests on two piers, one at each end. The best example of a simple beam bridge is a plank of wood laid across a stream. The weight of the bridge and anything on it travels directly downward and is supported by the piers. It works based upon the principles of compression
. and tension. The top edge of the beam is compressed while the bottom edge is stretched and lengthened due to tension. Many beam bridges use concrete and steel beams to support the weight load as the bridge compresses and bends. The size and height of the beams control the distance that the bridge can span. A simple beam bridge is used to span a distance of approximately 250 feet or less. Longer distances can be spanned by connecting a series of simple beam bridges into what is known as a continuous span. In order to create taller beams, trusses are added for reinforcement. A truss is a construction of lattice that supports and strengthens the beams.
