The authors investigated the dynamic behaviour of the San Silvestro belfry in L’Aquila (Italy). The 2009 earthquake in L’Aquila caused severe damages to the entire masonry complex. Extensive rehabilitation works, ended in 2019, repaired the structure and enhanced its seismic safety. In this paper, the authors discuss three aspects typical of masonry towers by interpreting the outcomes of Operational Modal Analysis carried out on December 2019: the interactions between the tower and the masonry complex, the dynamic effects of the bell, and the seismic reliability assessment of the tower. Specifically, the experimental mode shapes drive the estimation of an equivalent cross-section, whose principal axes of inertia match with the directions of oscillation of the mode shapes, and the parameters of an equivalent cantilevered beam roughly representative of the tower dynamics. In a second step, a two-degrees-of-freedom analytical model simulates the dynamic coupling between the tower and the more massive bell. The response of the system to a set of seven strong-motion earthquakes yields the assessment of the bell effects over the seismic performance of the masonry tower.
The city of L’Aquila (Italy) includes a significant amount of masonry palaces erected from the middle of the 13th century up to the first half of the 20th century. This paper focuses on the seismic response of a masonry palace built during the first half of the 20th century and characterized by regularity in plan and elevation. The authors investigate the seismic response by varying a suite of modelling parameters that express the actual scatter of the mechanical properties typical of the masonry palaces erected in L’Aquila. The authors discuss the seismic performance exhibited by this building during the 2009 earthquake. Then, they assess the sensitivity of the selected building’s seismic performance via non-linear static analysis to the mechanical properties of masonry, the in-plane stiffness of the floors, and the mechanical resistance of the spandrels. The parametric analysis shows that the three variables markedly affect the shear resistance, the ultimate displacement, and the behavior factors. The fragility functions were then estimated from the results of non-linear static analysis. A significant scatter of the probability of collapse for the considered limit states reveals the limitations of typological approaches for masonry palaces.
Masonry towers, located in seismic zones, are vulnerable and prone to damages up to compromise their stability. The scatter of data on the mechanical properties of masonry, geometry and boundary conditions determine a lack of building knowledge on their expected behaviour. Therefore the assessment of the seismic capacity represents a critical task. This paper contributes to the issue of seismic analysis of masonry towers, focusing a meaningful case study: the St.Silvestro belfry in L’Aquila, Italy. The tower, severely damaged by the 2009 earthquake sequence, underwent extensive restoration works, endeavoured to mitigate its vulnerability. The observed seismic damage, the performed no-destructive testing campaign and the accomplished rehabilitation measures are described in the paper. The authors appraised the actual seismic performances of the St.Silvestro belfry, reinforced by the last restoration works. At first, the Operational Modal Analysis (OMA) is carried out to enhance building knowledge. In a second step, a refined finite element model is calibrated on the results from OMA to seize the actual dynamic response. Ultimately, by using the updated finite element model, the authors estimate the fragility curves in terms of peak ground acceleration using truncated incremental dynamic analyses.
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