PSI - Issue 78

Marina Serpe et al. / Procedia Structural Integrity 78 (2026) 1000–1007

1001

1. Introduction URM buildings, widely present in historic centres across seismically active regions such as Southern Europe, South Asia, and Latin America (Frankie, Gencturk, and Elnashai 2013; Ozcebe and Crowley, n.d.), have consistently demonstrated a high vulnerability to earthquakes, due to the intrinsic characteristics of masonry, most notably its brittle behaviour, low tensile strength, and poor ductility (Lourenço et al. 2011; Mendes and Lourenço 2014). Additionally, post-earthquake investigations have frequently reported that the actual seismic capacity of these structures is significantly lower than predicted (Parisi and Augenti 2013; Bhagat et al. 2018). This is mainly due to the fact that, in recent years, research has strongly focused on the seismic vulnerability assessment of masonry structures without considering that an earthquake may occur after the structure has already been subjected to other actions during its service life. Even if these actions are of lower intensity, they may have compromised the structural capacity, leading to an overestimation of the actual seismic performance. One of the main contributing factors is pre-existing damage caused by differential foundation settlements, which often occur due to soil consolidation, groundwater level variations, or anthropogenic factors. Despite their relevance, such effects are typically excluded from conventional seismic vulnerability models, which generally assume undamaged initial conditions. Although the seismic behaviour of URM buildings has been extensively investigated using nonlinear static and dynamic analyses, studies explicitly addressing the combined impact of foundation settlements and seismic loading are limited (Loli et al. 2012; Negulescu et al. 2014; Couto, Bento, and Gomes 2020). Existing research often focuses on simplified structural configurations or isolated effects (Burland, Standing, and Jardine 2001; Skempton and Macdonald 1956; Boscardin and Cording 1989; Burland JB, Wroth CP 1974; Polshin DE, Tokar RA 1957), rarely capturing the complex interaction between settlement profiles and structural features (Giardina et al. 2013). Moreover, the development of fragility curves incorporating cumulative damage remains underexplored. This study aims to fill this gap by investigating how prior settlement-induced damage influences the seismic response of URM façade. A numerical strategy based on a semi coupled approach for settlement application and nonlinear static (pushover) analysis is employed (Serpe Marina et al. 2025), using a homogenised continuum damage model in a two-dimensional finite element environment. Several façade configurations are analysed in Section 4,, accounting for geometric and structural variations and different settlement profiles (see Section 3). Settlement is modelled as imposed vertical displacements at the base of the façade using a semi-coupled approach. The main output of the study consists in the development of cumulative fragility curves that quantify the progressive degradation of seismic capacity due to settlement with the aim of identifying the most demanding differential settlement scenarios on the defined façade population. 2. The objective and methodology The first step of the work consisted in the definition of a consistent set of URM façade configurations used as the basis for all numerical analyses. Each configuration was analysed under two conditions: with and without prior foundation settlement. This approach enables a direct comparison of the structural response evaluating cumulative fragility curves derived either under seismic action only or under seismic action following the application of different foundation settlement scenarios. To this end, a comprehensive numerical strategy is employed (Serpe Marina et al. 2025), structured into three main phases and corresponding sub-steps, as summarized below (Fig. 1): Phase 1: Definition of Case Studies: • Step 1.1 : Selection of reference geometry; • Step 1.2 : Parametric variation of geometrical and structural features; • Step 1.3 : Definition of settlement scenarios. Phase 2: Numerical Modelling and Pushover Analyses: • Step 2.1: Selection of the numerical modelling; • Step 2.2 : Pushover analysis without settlement; • Step 2.2 : Post-Settlement pushover analysis. Phase 3: Fragility Curves Derivation: • Step 3.1 : Evaluation of capacity curves; • Step 3.2 : Definition of seismic demand and limit states; • Step 3.3 : Derivation of fragility curves.