On the collapse of masonry arches

The principles of limit analysis of masonry arches are based upon the assumptions that the material has zero tensile strength, infinite compressive strength and that the voussoirs do not slide with respect to each other [1,2]. The first hypothesis, which may be considered quite conservative when the voussoirs are joined by mortar, is rendered realistic by the possibleformation of fractures due, for example, to the subsiding of springings. The second hypothesis, on the contrary, is by no means conservative - it can be justified by observing that in many cases collapse of a structure is due to mechanisms which render it kinematically undetermined despite the fact that the magnitude of the stress reached in the masonry is low. The thirdhypothesis, due to Coulomb [3], presupposes that friction between the voussoirs is sufficient to prevent their sliding. Clearly, in applications it must be verified, on a case by case basis, that these second and the third hypotheses are justified