Seismic assessment of a medieval masonry tower in Northern Italy by limit, non-linear static and full dynamic analyses

A comparative numerical study on a 12th-century masonry tower located in northern Italy is described. To assess the safety of the tower under seismic loads, different numerical analyses have been performed: nonlinear static, limit, and nonlinear full dynamic analyses. In the first two cases, a full three-dimensional (3D) detailed finite element model (FEM) is adopted, changing the seismic load direction and assuming different hypotheses for the interconnection between the core and the external walls. When dealing with the FEM incremental analysis, a commercial code is utilized assuming for masonry a smeared crack isotropic model. For limit analysis, a noncommercial full 3D code developed by the authors is utilized. It provides good estimates of limit loads and failure mechanisms to compare with standard FEM results. The dynamical analyses have been performed by a specific two-dimensional (2D) rigid body and spring model (RBSM), accounting for the asymmetries along the thickness and the irregularities of thickness of both the external and internal walls in an approximate but realistic way. Four different accelerograms are utilized—passing from low to high seismicity zones—to evaluate the performance of the tower under dynamic loads. From numerical results, the role played by the actual geometry of the tower is envisaged, as well as a detailed comparison of failure mechanisms provided by the incremental FEM and limit analysis is provided. In all cases, the numerical analysis has given a valuable picture of possible damage mechanisms providing useful hints for the introduction of structural monitoring.