Out of plane behaviour of unreinforced masonry walls

The behaviour of unreinforced masonry walls has been widely investigated in order to assess the seismic vulnerability of masonry structures. Even if partial analyses are not sufficient for a full structural analysis under seismic actions, they can be used to have quick estimation of both collapse load and failure mechanisms. Simplified out-of-plane collapse mechanisms, taking into account connections with floor and transversal walls, are considered to evaluate the behaviour of masonry walls subjected to out of plane forces. In general cantilever walls and walls supported only at the top and bottom edges can be represented as equivalent SDOF system, in order to evaluate by simple static analysis the limit horizontal force at the threshold of rocking, assuming that the wall has cracked and hence the tensile strength of the mortar can be neglected. Similarly, the displacement at the threshold of overturning can be obtained from that simple kinematic model. The value of the collapse load and the consequent load-displacement behaviour is strongly related to the way of computing the displacements and to the way of cracking. This paper presents some remarks on the evaluation of the effective secant stiffness of an unreinforced masonry wall in out of plane loading. Comparisons with the Priestley model are shown.