Seismic vulnerability assessment of masonry structures damaged by ground settlements: Parametric nonlinear static FEM analysis and fragility curves

The evaluation of vulnerability in unreinforced masonry (URM) structures is a significant area of research and engineering practice, driven by the increasing need to understand and mitigate risks for these constructions. Recent decades have seen a growing focus on assessing seismic vulnerability in response to historical destructive earthquakes, and, simultaneously, on understanding the impact of ground movements. The occurrence of settlements is a natural process following the completion of the building itself but it can also result from natural phenomena (e.g., subsidence, landslides) or anthropogenic activities (e.g., tunnelling, new construction). Recent studies have thus emphasized soil-structure interaction modelling and multi-hazard analysis, accounting for simultaneous or successive hazards. However, limited research exists on how settlement-induced damage may influence the seismic vulnerability of existing URM structures. This thesis investigates the combined effects of settlement and seismic actions on URM vulnerability through a detailed methodology, validated on available experimental data, integrating numerical modelling and parametric analysis. The first part focuses on developing a robust modelling strategy, supported by experimental tests that simulate horizontal loading and settlement. This section addresses material calibration, interface properties, and masonry-specific elements, validated through independent responses to settlement and seismic loading. The study then examines the impact of foundation settlement on URM seismic capacity using a finite element model (FEM) with nonlinear static analysis to capture damage patterns and pushover behaviour. Parametric analyses consider factors such as wall configuration, diaphragm rigidity, and structural dimensions to elucidate how settlement affects seismic response. These findings culminate in the development of fragility curves that quantify seismic vulnerability under pre-existing settlement conditions, with damage assessment, performance point calculation, and curve derivation methodologies. A case study applies this methodology to Montecassino Abbey, illustrating the practical implications of combined settlement and seismic action for historic masonry structures. Through geometrical modelling, modal analysis, and nonlinear static analyses, the study identifies specific vulnerabilities and provides insights into the interplay between settlement and seismic response. The results contribute to a deeper understanding of URM vulnerability under combined actions, offering an improved framework for risk assessment and preservation of heritage and masonry structures.