Fragility assessment of unreinforced masonry walls undergoing earthquake-induced local failure mechanisms

Damage observations from strong earthquakes show that unreinforced masonry buildings have exhibited recurrent local failure mechanisms and constitute a serious life-safety hazard. This contribution is aimed at evaluating the fragility functions for unreinforced masonry walls in the presence of local failure mechanisms induced by out-of plane loading The out-of-plane response consists of the overturning of the entire or apart of the wall insufficiently connected to the rest of the structure. The wall can be idealized as a number of rigid bodies undergoing rocking motion. They are assumed to undergo one-sided rocking or vertical spanning strip wall displacing as an assembly of a coupled rigid body. In this study, we use a set of 44 ground motions from earthquake events that occurred in Italy from 1972 to 2017. For any given wall undergoing a specific collapse mechanism, the probability of collapse is evaluated through a Multiple Stripe Analysis (MSA). Then, a fragility curve is fitted to the MSA datapoints. The procedure outlined may be extended to obtain typological fragility functions as a combination of the fragility curves corresponding to the various mechanisms analyzed. A preliminary application of the procedure to the historical centre of Ferrara, Italy, is described.