Overturning of the facade in single-nave churches under seismic loading

The out-of-plane collapse of the facade represents one of the major threats and the most frequent cause of damages of churches due to strong earthquakes. Due to the slenderness of the facade and the lack of adequate connections to the side walls and the wooden roof, the seismic action can trigger the overturning. A detailed assessment is therefore required to judge whether or not to intervene. This paper presents an approach for the seismic assessment of the stability of the facade, through a discrete element model based on a photographic survey, with the aim of representing the actual geometry and arrangement of the stone units and their effects on the kinematics of the overturning. The collapse mechanism is simulated with both, quasi-static pushover and dynamic pulse-based analyses and the results compared to those of conventional rigid-body kinematics. The proposed approach is then applied to seven masonry churches that suffered severe damages during the 2009 L'Aquila (Italy) earthquake and the failure mode provided by the analyses is compared to the damages caused by the earthquake. The method is able to give a reliable estimate of the expected failure mechanism, taking into account the quality of the masonry and the connections to the side walls, while also providing the seismic acceleration required to trigger the motion and the ultimate displacement beyond which collapse occurs.