Fragility Functions for Local Failure Mechanisms in Unreinforced Masonry Buildings

Abstract

The unreinforced masonry buildings can be present frequent local failure mechanisms and represent a serious life-safety hazard as recent strong earthquakes have shown. Compared to new building, existing unreinforced masonry buildings prone to be more vulnerable, not only because they have been designed without seismic or limited loading requirements, but also because horizontal structures and connections amid the walls are not always suitable. Out-of-plane collapse can be caused by important slenderness of walls also when connections are effective. The purpose of this paper is to evaluate fragility functions for unreinforced masonry walls in the presence of local failure mechanisms considering the out-of-plane response. The wall response, very often, can be idealized as rigid bodies undergoing rocking motion. Depending on its configuration, a wall is assumed either as a rigid body undergoing simple one-sided rocking or an assembly of two coupled rigid bodies rocking along their common edge. A set of 44 ground motions from earthquake events occurred from 1972 to 2017 in Italy is used in this study. The likelihood of collapse is calculated via Multiple Stripe Analysis (MSA) from a given wall undergoing a specific ground motion. Later, the single fragility functions are suitably combined to define a typological fragility function for a class of buildings. The procedure is applied to a historical aggregate in the city center of Ferrara (Italy) as a case study. The fragility functions developed in this research can be a very helpful tool for estimating damage and economic loss for unreinforced masonry buildings and for a seismic assessment on a regional scale.