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Civil Engineering
Bridges and Tunnels

Does an arch bridge hold more weight than a beam bridge?


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May 29, 2008 8:16PM

Yes. An arch bridge is one of the more efficient ways of building and maintaining a bridge. Beam bridges are not as efficient. For a given span and height, an arch bridge will carry a greater load using less material. The beam structures of a beam bridge can be constructed of wood, reinforced concrete or steel (in increasing order of strength). The beams, however, must be supported by piers or an abutment at each end, which can be made out of concrete, masonry, stone, or steel (or combination thereof). The arch structure of an arch bridge can be constructed of wood, reinforced concrete, steel, or masonry, and the arch can be supported by abutments as described above, or the arch can extended down to the foundation itself. The primary advantage of an arch is that stresses caused by the load on the bridge are converted primarily into compressive stresses that are carried along the arch into the ground. Materials like stone, masonry and concrete are particularly good at carrying these compressive stresses. In contrast, loads on a typical beam-type bridge creates large tensile stresses on the bottom of the beams. Since stone, masonry and unreinforced concrete have very little capacity to withstand tension, none of these materials can be used to make a reliable and efficient beam-type bridge of any significant span.