A specific out-of-plane model for the dynamic analysis of masonry façades and estimation of cumulative seismic damage

The seismic damage suffered by masonry buildings, especially historical monuments, depends on a multiplicity of factors that determine their structural vulnerability and, of course, on the seismic hazard. Engineering approaches need a manageable and effective modeling of these aspects, but it is hard to admit that hazard and vulnerability can be easily synthesized by scalar measures. An advanced and rationale approach for the assessment needs to manage the mechanical complexity of masonry, whose seismic performance depends on the overall structural geometry; the masonry texture, often consisting of multiple layers; quality of blocks and mortar. It must also cope with the manifold dynamic features of earthquakes, including: amplitude of ground acceleration; frequency content; duration of the most intense part. Furthermore, it should be considered the possible occurrence of destructive events in a close sequence, which is instead rarely considered. The numerical study of these aspects requires extensive nonlinear dynamic analyses by means of specific models. Restricting the attention to the out-of-plane response of church façades, the paper presents the background and choices adopted in the formulation of a computational heuristic model that manages the hysteretic mechanical response by accounting for internal texture. It is shown that it is essential to carry out dynamic analyses to understand the different damage mechanisms and contribution of higher vibration modes. Finally, the availability of a model with excellent computational performance is exploited to study the cumulative damage in the case of a sequence of destructive seismic events.