Abstract

The extensive damage occurred to the Italian historical and architectural heritage during the 2016-2017 earthquake sequence, and particularly to unreinforced masonry churches, highlights the need to better recognize the vulnerability of religious buildings. A sample of 158 churches belonging to the four stricken regions is studied and their performance analysed statistically. Structural behaviour of these churches is described in terms of mechanisms affecting the so-called macroelements, being portions of the building behaving more or less independently. In order to define fragility curves correlating the damage related to each collapse mechanism against ground motion intensity and churches’ specific characteristics, the observed behaviour of the sample is herein analysed by means of statistical procedures accounting for possible local collapse mechanisms. Several regressions strategies are considered, accounting for vulnerability modifiers increasing/reducing the vulnerability of each macroelement, since the severity of shaking alone is not capable to fully explain the observed damage, strongly influenced by structural details that can worsen the seismic performance or improve it through earthquake-resistant elements. A synthetic damage index, purely based on observed data, is used to summarise the overall severity of damage related to relevant mechanisms, highlighting the contributions of ground shaking and building vulnerability. Results show the relevance of the proposed multi-linear regression models for the national heritage of churches and the advisability of extending mechanism-based regressions to other countries besides Italy. The proposed global damage index can be used as predictive tool to support seismic vulnerability mitigation at a territorial scale.