Empirical fragility curves for macro-elements and single mechanisms of churches damaged during the 2016-2017 Central Italy seismic sequence

The churches represent the most widespread building typology within the monumental masonry heritage present in the Italian territory. A special attention needs to be paid to the assessment of the vulnerability of these structures because of the particular architectural features (slender walls with large openings, wide halls and huge vaults, large façades, etc…). This paper presents several statistical analyses carried out on a wide database that collects damage information and structural characteristics of a large sample of masonry churches (2884) inspected after the 2016-2017 Central Italy seismic sequence. The collected information is used for developing empirical fragility curves starting from the damage probability matrices (DPMs) for discrete intervals of PGA (peak ground acceleration), with reference to the following three damage estimates: i) the global damage referred to the whole church, ii) the damage referred to single macro-elements, and iii) the damage referred to single mechanisms. The fragility functions are determined via the maximum likelihood estimation method and adopt a lognormal cumulative function to define the exceedance probabilities for the five damage levels provided by the European macro-seismic (EMS) scale. The fragility curves related to the three damage estimates are compared to each other to identify the weight of specific macro-elements and mechanisms in determining the global damage level and eventually to point out proper and specific interventions to reduce the vulnerability of the whole church.