Operational modal analysis, model update and fragility curves estimation, through truncated incremental dynamic analysis, of a masonry belfry

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.