Arch bridges pose a classic architecture and the oldest after the girder bridges. Unlike simple girder bridges, arches are well suited to the use of stone. Since the arch doesn't require piers in the center so arches are good choices for crossing valleys and rivers. Arches can be one of the most beautiful bridge types. Arches use a curved structure which provides a high resistance to bending forces. Arches can only be used where the ground or foundation is solid and stable because unlike girder and truss bridges, both ends of an arch are fixed in the horizontal direction (i.e. no horizontal movement is allowed in the bearing). Thus when a load is placed on the bridge (e.g. a car passes over it) horizontal forces occur in the bearings of the arch. Like the truss, the roadway may pass over or through an arch or in some cases.
Structurally there are four basic arch types:
- Three hinged
- Tied arches
The hinge-less arch uses no hinges and allows no rotation at the foundations. As a result a great deal of force is generated at the foundation (horizontal, vertical, and bending forces) and the hinge-less arch can only be built where the ground is very stable. However, the hinge-less arch is a very stiff structure and suffers less deflection than other arches. The two hinged arch uses hinged bearings which allow rotation.