Historical masonry building aggregates: advanced numerical insight for an effective seismic assessment on two row housing compounds

Historical masonry aggregates represent a large portion of the cultural heritage in Italy and are highly vulnerable to seismic actions, as shown by past seismic events. Typically, they are large and complex structures for which there is a lack of knowledge and information concerning the structural behavior, in particular as far as the response to seismic actions is concerned. This paper investigates the seismic response of two complex historical masonry aggregates located in Sora (Lazio region, Central Italy), through advanced 3D FE numerical simulations. For each aggregate, a detailed 3D FE model is developed and analyzed in the non-linear dynamic range, assuming that masonry behaves as a damaging-plastic material with almost vanishing tensile strength. The seismic performance of the two aggregates is evaluated in terms of damage distribution, energy density dissipated by tensile damage and maximum normalized displacements. The numerical analyses show the high vulnerability of the perimeter walls. In particular, the units at the extremities of the aggregate are subjected to large displacements, being not efficiently braced by the adjacent units and being subjected to the torsional effects induced by the seismic action. The presence of several openings is a fundamental feature that significantly decreases the strength of the perimeter walls, influencing the damage distribution in the aggregate mainly due to out-of-plane actions. The most damaged elements are generally the walls of the tall units without lateral support and the adjacent slabs covering large spans. Numerical results also show that the structural response of a single building unit is affected by the interactions with adjacent structural parts. Moreover, it can be stated that a preliminary structural assessment through kinematic limit analysis on partial failure mechanisms may be reliable only after a proper estimation of the different structural elements playing a role in the horizontal behavior (e.g. interlocking between walls, typology of masonry, distribution of horizontal loads, constraints and dead loads distribution, etc.). The obtained results will be also used in an accompanying paper to benchmark simplified approaches that can be employed by engineers in common design practice to quickly predict the seismic vulnerability of masonry aggregates and define the most suitable strengthening interventions.