Arch bridges are subject to the two basic forces – compression and tension – that are in effect for all bridges. In an arch bridge, the tension is so minimal that we say it is only in compression. This is because the force at work in an arch bridge is the squeezing force (–> <–)of compression. The pulling force of tension (<– –>) is negligible. How is this possible?
The arch stays together by being squeezed. This squeezing, or compressive, force moves outward along the curve of the arch. The arch can’t spread very far because it is being pushed back by the abutments – or legs – that serve as the foundation.
The compressional stress of the arch bridge is dissipated along the abutments and into the earth. If this were not the case, the bridge would collapse.