Seismic collapse analysis of unreinforced masonry buildings through applied element micro-modelling and crack width-based damage measures

Unreinforced masonry (URM) structures subjected to moderate-to-severe earthquake ground motion often experience a poor performance, characterised by extensive cracking phenomena and the activation and development of collapse mechanisms. This produces high repair costs and a severe threat to human life. Furthermore, outward projection and accumulation of debris may reduce road serviceability, undermining rescue efforts and increasing post-event downtime. In this study, the suitability of the Applied Element Method – a discrete crack, rigid body and springs-based numerical technique – to capture damage spread, collapse mechanism activation and debris projection phenomena is tested against experimental data. Fracture energy-based softening laws are employed, improving numerical accuracy over the standard brittle failure models commonly implemented within AEM tools. The validated models are then used to assess the seismic performance of URM buildings under varying masonry quality, and hence mechanical properties. The study leverages on the inherent advantage of the AEM, that is, explicit simulation of cracking phenomena and body fragmentation with lower computational demand than other advanced numerical techniques, in order to: (i) simulate complex failure mechanisms, eventually leading up to collapse activation and subsequent stages of debris formation and accumulation; (ii) introduce novel damage measures that are able to explicitly quantify crack propagation and severity in URM load-bearing structures.