Non-smooth Dynamic Analysis of Local Seismic Damage Mechanisms of the San Felice Fortress in Northern Italy

The May 2012 seismic swarm, with epicenter in the Modena plane, in Northern Italy, had severe consequences on the historical buildings of the area. In particular, the fortified structures suffered specific, recurring damage and collapse mechanisms. The present paper deals with the case of the San Felice sul Panaro Fortress, which saw the collapse of 4 out of 5 towers and many other global and local effects. The work starts with an in-depth knowledge path, as a fundamental premise for a conscious intervention. The combination among historical analysis of the building, seismic history of the site, materials and pathological survey, structural identification, on-site inspections and tests, allowed to interpret the crack pattern and to identify the damage mechanisms activated by the earthquake, successively examined with specific structural analyses. In particular, the present paper concentrates on the numerical modelling of the identified local mechanisms, adopting a type of analysis first developed at the University of Parma for applied mechanics, based on the use of non-smooth dynamics software, through a Differential Variational Inequalities (DVI) formulation specifically developed for the 3D discrete elements method. It allows to follow large displacements and the opening and closure of cracks in dynamic field. Once the modelling instrument was calibrated, thanks to the comparison with the real damages previously inspected, it was also applied to foresee the behavior of the same mechanisms with different actions and with different types of strengthening.