Effects of seismic sequences on masonry structures

In this work, the seismic behaviour of UnReinforced Masonry (URM) structures under repeated earthquakes is investigated. Such analysis is carried-out by using a purposely-developed non-linear software that describes the hysteretic behaviour of a masonry panel through an appropriate phenomenological law. First, results obtained from a series of non-linear dynamic analyses on a single degree of freedom (SDOF) system, which represents the typical cyclic response of an unreinforced masonry structure, are presented. The seismic sequences adopted for the analysis are taken from international databases and are selected on the base of the Peak Ground Acceleration (PGA) of the events following the mainshock. The selected aftershocks have a PGA equal or almost similar to the mainshock, in such a way to significantly influence of the required ductility for the analysed system and, consequently, on the damage index used to quantify the structural degradation. The obtained results are presented in terms of inelastic response at constant ductility or strength. On the base of the collected results, modifications on the behaviour factors commonly adopted in seismic design are proposed. Finally, a SDOF system representing a typical masonry structure subjected to the seismic sequence of Central Italy (2016) has been analysed with the aim to highlight the damage evolution.