Statistical analysis of damages to masonry churches after the 2017 Ischia earthquake

Latest Italian earthquakes have significantly highlighted that heritage masonry buildings, especially churches, are considerably vulnerable to seismic actions. Though usually made of good quality materials, churches are characterized by highly vulnerable structural morphologies and architectural configurations, such as significant dimensions, wide halls, thin long span vaults, slender towering or projecting parts, slender walls with large openings. On 21st August 2017, an earthquake struck the Ischia Island causing several damages to both ordinary and heritage buildings. During the emergency phases after the event, many churches were surveyed and the damage evaluation was carried out by filling in the II level survey form (A-DC) in situ. An interesting database made of 27 churches was, thus, created aimed to carry out detailed analysis of the recorded damages and to realize damage probability matrices, useful to implement fragility curves based on an “observational approach”. Both global damage index and activation of mechanisms were investigated. Considerations about the correlation between vulnerability index and observed damage level were also presented. Finally, for a homogenous class of churches, a predictive formulation of the mean damage was assessed and compared with other formulations available in the literature and obtained according to a similar approach.