Simplified discontinuum out-of-plane seismic analysis of archetypal Italian masonry church gabled façades

Abstract Post-earthquake surveys have highlighted that the seismic behaviour of masonry churches is often characterized by the independent activation of recurrent failure mechanisms of distinct architectural components, known as macroelements. Among these, the out-of-plane (OOP) overturning of the main façade has emerged as one of the most critical vulnerabilities, particularly in historic Italian single-nave churches made of unreinforced masonry (URM). This study presents an in-depth parametric assessment of the OOP-governed seismic response of archetypal Italian URM gabled church façades through a simplified discontinuum numerical strategy implemented in a Distinct Element (DEM) modelling framework, developed in 3DEC. Novel contributions include 1) the generation of evidence-based DEM-compatible simplified archetypal geometries for discontinuum OOP failure analysis, 2) the concurrent consideration of façade aspect ratio, thickness slenderness, material variations and the presence of interlocking, 3) the possibility of capturing three-dimensional OOP mechanism evolution and related force-displacement variations at exceptionally high-resolution, 4) inclusion of both forced and non-forced OOP mechanisms. The proposed nonlinear static analysis methodology, which outperforms previously developed evaluation procedures, introduces a newly optimized formulation that captures and controls both the initial elastic and post-peak behaviour of the pushover curve in 3D with unprecedented efficiency. To explore the influence of specific church typological factors, a semi-automated parametric modelling is employed via Grasshopper in Rhinoceros 3D. This visual programming framework enables the rapid generation of multiple URM façade geometries by adjusting wall dimensions, slenderness ratios, interlocking patterns, and roof shapes, facilitating the creation of the 54 case-study models considered herein. The geometrical parameters selected were based on a database of over 600 churches surveyed after the 2016 Central Italy seismic sequence, while the URM mechanical properties were defined according to the Italian National Standards and statistical sampling. The proposed discontinuum framework offers a valuable tool for the detailed seismic assessment of archetypal Italian URM gabled churches, providing deeper insights into the influence of specific typological factors on their OOP response.