Seismic vulnerability of Italian masonry churches: The case of the Nativity of Blessed Virgin Mary in Stellata of Bondeno

In this paper the problem of seismic vulnerability of masonry churches is analysed with reference to the Nativity of Blessed Virgin Mary ecclesiastic complex in Stellata of Bondeno (Italy). This religious construction is composed of a church, two bell towers, a cloister and the Saint Domenico's oratory. The church, made of masonry brick stones, is characterized by a single hall with chapels, which is divided into three parts by arches, and has an apse elevated by a few steps with reference to the hall. The study herein presented is carried out according to the Italian Standards and Guidelines on Cultural Heritage. In a first step, the seismic risk coefficients both at Damage Limit State (a DLS) and Ultimate Limit State (a ULS) are evaluated by using the 3Muri calculation software for masonry structures. These coefficients indicate the ratio between the ground acceleration leading towards attainment of the two mentioned limit states and the PGAs of the site referred to a given reference return period. Afterwards, the variability of such coefficients is examined by changing both the masonry type and the seismic zone in order to detect the worst situations on the Italian land. In a second analysis step a comparison among the seismic risk coefficients a ULS and the damage index calculated through a fast method provided in a suitable form by the Italian Civil Protection Department is proposed. Moreover, overturning mechanisms of facades are checked by using the 3Muri software with the ultimate goal to compare the predictive theoretical results with the real damages detected after the 2012 Emilia Romagna earthquake. Finally, in order to obtain a more precise assessment of the seismic behaviour of the church under study, linear and non-linear dynamic analyses are performed on a 3D FEM model setup through the ABAQUS software package.