Development of Fragility curves for the Seismic Risk Assessment of a School Buildings Portfolio at Regional scale

This research aims to develop seismic fragility curves for unreinforced masonry (URM) school buildings, essential for assessing seismic risk and designing effective mitigation strategies. The research addresses key challenges in fragility assessment, including inconsistencies in damage criteria and variability in building stock data. Section 5 investigates the reliability of NSPs through comparison with NDPs using cloud analysis. The capacity spectrum method (CSM) emerged as the most consistent NSP for URM buildings. To address its conservative bias, a correction factor was applied to refine the DBV-Masonry approach, which was subsequently used to analyze URM schools in Friuli-Venezia Giulia, Italy. Sections 6 and 7 of this research delve into comparing seismic vulnerability assessment methods for unreinforced masonry (URM) school buildings in Italy’s Friuli-Venezia Giulia (FVG) region. Section 6 focuses on the simplified mechanical-analytical DBV-Masonry approach and its comparison with similar methods, such as the Firstep-M_PRO approach developed by the University of Trieste. These analyses highlight the implications of differing methodological choices within nonlinear static procedures (NSP). The section provides a comprehensive analysis of seismic fragility, aiming to inform risk mitigation strategies and improve the resilience of URM school buildings to earthquakes. The DBV-Masonry approach, validated against a numerical analytical procedure (Cloud+IDA method), was used to assess a sample of schools in the FVG region. Section 7 describes this numerical approach in detail, employing nonlinear dynamic analyses (NLDAs) for validation. Seven URM school buildings were modeled using the Tremuri software, which implements a 3D equivalent frame (EF) approach. This method, widely endorsed for its ability to balance accuracy and computational efficiency, focuses on in-plane responses of masonry walls while assuming box-like behavior that limits out-of-plane mechanisms. Fragility curves generated using the DBV-Masonry approach were validated by comparing them with results from NLDAs, with the latter serving as the reference solution. Section 7 further explores the Cloud+IDA methodology, emphasizing its use in defining performance levels and calculating intensity measures, such as peak ground acceleration (PGA), for seismic vulnerability assessment. Buildings were carefully selected for their well-documented characteristics, minimizing input uncertainty and ensuring robust validation. Fragility curves derived from NLDAs were compared with empirical and heuristic approaches, as well as those developed in the MARS project. The iterative approach enhanced result reliability, particularly for limited analyses, and refined performance level definitions where current codes lack guidance. The research identifies the limitations of modeling techniques, particularly the exclusion of out-of-plane behavior. However, this assumption is justified for the studied buildings due to their structural features, such as rigid floors and reinforced concrete beams, which mitigate local failure mechanisms. In cases where out-of-plane responses may be critical, separate assessments are recommended. The thesis is systematically structured: Section 2 reviews methods for developing fragility curves; Section 3 introduces the DBV-Masonry and nonlinear dynamic procedures; Section 4 details the modeling of case study buildings; Section 5 evaluates nonlinear analysis methods; Section 6 reports results from the DBV-Masonry method and comparisons with numerical approaches; Section 7 discusses NLDAs and fragility curve development; and Section 8 presents conclusions and recommendations. This comprehensive approach enhances understanding of URM school vulnerabilities and provides a validated framework for future seismic safety improvements. By integrating seismic hazard, exposure, and fragility functions, this research bridges a critical gap, offering a validated framework to enhance the resilience of URM schools and guide seismic safety policies globally.