SFS INTERACTION WITH AND WITHOUT CROSS-INTERACTION BETWEEN THE FOUNDATIONS OF URM AGGREGATES

The paper focuses on the development of fragility curves of a masonry building aggregate located in Visso, a small village that was severely damaged by the 2016-2017 Central Italy earthquake. The historic center of Visso, like many others similar in Italy, is mainly made up of unreinforced masonry (URM) buildings erected in aggregate on relatively soft soils. So, site effects and soil-foundation-structure (SFS) interaction are likely to affect the seismic response of the URM buildings in the historic part of Visso, as recently highlighted by Brunelli et al. (2022a), who developed fragility curves through 300 Non-Linear Dynamic Analyses (NLDA) of 3D equivalent frame models, both in fixed and compliant-base conditions. The aim of this work is to evaluate the modification of the above fragility curves considering, in addition to the SFS interaction, also the cross interaction that occurs between closely-spaced foundations of the aggregate (FSFI), an aspect that has so far been denied. In this perspective, the static stiffnesses below the load-bearing walls of the Visso aggregate have been updated by introducing the group factors proposed by Zeolla et al. (2023) to englobe the foundationfoundation interaction. An initial comparison of results with and without cross-interaction was performed by comparing the impedance values, periods and equivalent damping of the coupled soil-structure system, and the simulated damage under the records of the 2016/17 Central Italy earthquake. Finally, the 300 NLDAs with the modified impedances were rerun to evaluate the cross-interaction effects in terms of fragility curves.