<P> Because no moments are transferred, thrust, as from an arch bridge, cannot be accommodated, so leading to innovative designs, such as lenticular trusses & bow string arches, which contain the horizontal forces within the superstructure . </P> <P> Beam bridges are not limited to a single span . Some viaducts such as the Feiyunjiang Bridge in China have multiple simply supported spans supported by piers . This is opposed to viaducts using continuous spans over the piers . </P> <P> Beam bridges are often only used for relatively short distances because, unlike truss bridges, they have no built in supports . The only supports are provided by piers . The farther apart its supports, the weaker a beam bridge gets . As a result, beam bridges rarely span more than 250 feet (80 m). This doesn't mean beam bridges aren't used to cross great distances, it only means that a series of beam bridges must be joined together, creating what's known as a continuous span . </P>

What determines the distancea beam bridge can span
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