SEISMIC FRAGILITY CURVES ACCOUNTING FOR SITE AND SOIL STRUCTURE INTERACTION EFFECTS ON URM BUILDINGS

Significant site-amplification effects have been observed in various historic centers following the recent seismic events in Italy (e.g., L'Aquila 2009, Emilia 2012, Central Italy 2016-17), but also examples of Soil Foundation Structure (SFS) interaction in ordinary unreinforced masonry (URM) buildings. In the past, SFS interaction effects were usually considered for masonry buildings only in slender or massive URM monumental structures. Following the latest observed evidence, this research aims to further investigate the role of site amplification and SFS interaction in the seismic response of URM residential structures. The final goal is to provide an effective procedure to consider these effects in large-scale risk assessment as well. The first part of the research validated the numerical approach to analyze the SFS interaction by reproducing the seismic response of the Visso school affected by the earthquake sequence in central Italy. This school constituted a very emblematic case study, since it was permanently monitored by the Italian Department of Civil Protection and suffered very severe damage, allowing validation even in a highly nonlinear phase. The procedure is based on the decoupled approach. Therefore, the input motion of the foundation is calculated from the site response analyses and the structural performance is analyzed through a structural model with springs at the base and characterized by equivalent damping. This school's validated procedure and numerical model were exploited to derive fragility curves that include site effects and SFS interaction under different subsurface conditions. The predicted damage probability was also compared with the results obtained from different amplifications of the simplified Code-compliant approach. Finally, the research was further generalized by considering multiple building types and different soil profiles. The structural types were inspired by the most frequent building types in the municipality of Visso, consisting of aggregate masonry structures. The set of derived fragility curves was finally applied to an urban scale to develop damage scenarios. In particular, the resulting damage under ground motion of the Central Italy earthquake was compared with that observed and predicted by existing faster and less accurate approaches, to assess the potential of the developed tools also to support possible future large-scale mitigation policies.