An arch may be defined as a plane-curved bar or rib supported and loaded in a way that makes it act in direct compression. For example, the structure in Fig. 1a is a parabolic symmetrical arch that is loaded with a distributed load that varies linearly over the span L of the arch. It is fixed at end A and supported by an immovable hinge at end B. The horizontal distance between the end supports of the arch is the span of the arch, and the line AB joining its points of supports is the springing line.