UnReinforced Masonry (URM) buildings represent a large part of the Italian building stock.
The fragility functions developed in this research can be a helpful tool for assessing seismic damage and economic losses in unreinforced masonry buildings on a regional scale. The procedure is applied to a historical aggregate in the city center of Ferrara (Italy) as a case study. Then, the single fragility functions are suitably combined to define a typological fragility function for a class of buildings. The likelihood of collapse is calculated via Multiple Stripe Analysis (MSA) from a given wall undergoing a specific ground motion. A set of 44 ground motions from earthquake events occurred from 1972 to 2017 in Italy is used in this study. In particular, depending on its configuration, a wall is assumed either as a single rigid body undergoing simple one-sided rocking or a system of two coupled rigid bodies rocking along their common edge. In the case of slender walls with good material properties, the OOP response can be modeled with reference to an assembly of rigid bodies undergoing rocking motion.
The purpose of this paper is to derive typological fragility functions for unreinforced masonry walls considering OOP local failure mechanisms. Also, Out-Of-Plane (OOP) mechanisms can be caused by significant slenderness of the walls even if connections are effective. Compared to new buildings, older unreinforced masonry buildings are more vulnerable, not only because they have been designed without or with limited seismic loading requirements, but also because horizontal structures and connections amid the walls are not always effective. Unreinforced masonry buildings undergoing seismic actions often exhibit local failure mechanisms which represent a serious life-safety hazard, as recent strong earthquakes have shown.
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