Modelling the out-of-plane seismic behaviour of masonry walls by rigid elements

A computational model for evaluating the dynamical response and the degradation of masonry façades subjected to out-of-plane seismic actions is presented. The lateral actions are often the main cause of damage for the large plane walls of monuments subjected to strong earthquakes. This is particularly evident for the façades and lateral walls of old masonry-built churches, where the crack patterns tend to subdivide the plane walls into a number of rigid blocks. The model assumes such walls as a series of quadrilateral plane rigid elements connected to each other in the middle of their adjoining sides. Only the out-of-plane displacements are considered, thence the connections are regarded as spherical elasto-plastic joints which allow rotations whose axis is in the plane of the undeformed wall. The hysteretic characteristics of these joints are defined so as to approximate the brittle behaviour of masonry material and the degradation due to cyclic loadings. The numerical results obtained using a limited number of elements show that the global out-of-plane response of the masonry walls and the mechanical degradation at each connection are in accord with the observed behaviour of real churches hit by strong earthquakes