Numerical evaluation of seismic performance of masonry façades damaged by foundation settlements

Settlements occurring at the foundation level are commonly observed in construction practice. They are often responsible for structural damage that can significantly compromise the stability of buildings or their capacity to resist to exceptional loads, such as earthquakes. Most studies in the literature neglect the influence of settlements on the evaluation of the seismic capacity of buildings. Alternatively, studies focus exclusively on the evaluation of settlement effects without considering how they may impair structural performance under seismic loading. This gap is particularly critical for existing unreinforced masonry (URM) buildings, which are inherently vulnerable to seismic actions. This study aims to numerically investigate the impact of foundation settlements on the seismic performance of URM façades. To this end, nonlinear static analyses based on the Finite Element Method (FEM) are carried out on 2D models of masonry façades. A parametric study is performed by changing key factors related to settlement, such as the magnitude, position, and width of vertical displacements, as well as structural features like wall height and width, size and position of openings, and floor stiffness. The results show that even small differential settlements (≈10 mm) may significantly increase the susceptibility to seismic damage, leading to measurable reductions in lateral stiffness and strength, particularly in slender walls with a high percentage of openings and flexible diaphragms. Higher settlements (≈30 mm), especially when laterally concentrated over a limited portion of the base, may strongly alter the failure mechanism and further amplify seismic vulnerability. Conversely, the presence of rigid diaphragms significantly mitigates damage concentration and enhances global displacement and energy dissipation capacity. Overall, the study highlights that specific combinations of geometric and geotechnical weaknesses, namely reduced resistant sections (i.e., higher opening ratios) and slender walls subjected to lateral base settlements concentrated over a limited portion of the foundation, can significantly increase seismic vulnerability and alter the prevailing failure mode.