Strategies for the nonlinear seismic modelling of masonry buildings in aggregate

The paper presents a study about the strategies for the numerical modelling and analysis of masonry buildings in aggregate, a complex configuration typically encountered in Italian historical centres in which structural units are built in continuity next to each other and that is often characterized by a high irregularity, both in plan and elevation. The complexity of morphological articulation, especially in the case of historical masonry, is combined to the inherent difficulties associated to the modelling of masonry, which is a composite, highly inhomogeneous and anisotropic material, characterized by significant nonlinear, irreversible, and dissipative phenomena in the mechanical response, which should be adequately accounted for in a structural model. Some case studies of masonry building blocks representative of real configurations which can be found in Southern Italy (Puglia) have been numerically modelled by a detailed 3D FEM approach, assuming a nonlinear constitutive model with plasticity and damage for masonry. In order to investigate the influence of uncertainties and incomplete knowledge, different models have been analysed, by varying some of the main geometrical and mechanical parameters, performing preliminary modal analyses and a set of nonlinear time history analyses. In particular, the influence of floor deformability on structural response was investigated, first in the linear field, by analyzing the variation of modal parameters, and then through a set of dynamic analyses with natural accelerograms, in terms of damage distribution.