The Mechanism Method in the Analysis of Two-Span Masonry Arch Bridges

Stone and masonry arches characterize the structure of a large number of existing bridges, built in the past and still in service under more and more increasing traffic loads. The evaluation of safety of such bridges is therefore of interest for the bridge owners and responsible and quick and reliable procedures of analysis are certainly useful, at least for a preliminary approach. The mechanism method certainly satisfies these requirements. The main hypothesis is that stone arches fail by forming pin joints, as demonstrated by old but also by recent experimental studies. Furthermore, the assumption of masonry with no tensile strength and infinite compressive strength was done. This last hypothesis was removed in a previous paper, by assuming a rigid-perfect plastic behavior in compression. The load factor and the corresponding collapse mechanism are found by using an iteration procedure. In this paper, this model is used for the case of a two-span arch bridge, so that the collapse mechanism involves plastic hinges in the two arches and the pier.