Soil–Structure Interaction Effects on the Dynamic Response of the Historical Masonry Building “Istituto per Ciechi Adulti Vittorio Emanuele II” in Florence

This study examines the impact of soil–structure interaction (SSI) on the dynamic behaviour of the historical masonry building Istituto per Ciechi Adulti Vittorio Emanuele II in Florence (Italy). The structure, representative of late nineteenth-century institutional architecture, is characterised by large plan dimensions, significant mass, and foundations on soft alluvial deposits overlying stiffer soil layers. An integrated experimental–numerical methodology is adopted, combining ambient vibration testing with advanced finite element modelling. A detailed 3D numerical model of the building is developed and calibrated against experimentally identified modal parameters. Material and geometric properties have been defined through comprehensive surveys and literature benchmarks. SSI has been explicitly modelled via the direct method in OpenSees, allowing a realistic representation of the soil continuum and its interaction with the foundation system. Modal analyses are performed for both fixed-base and SSI configurations. The results show that the inclusion of SSI leads to significant reductions in the natural frequencies of the fundamental translational modes, while the associated mode shapes remain largely unchanged. These findings highlight the strong influence of soil flexibility on the global dynamic response of the building and demonstrate that SSI effects are particularly relevant for large historical masonry structures founded on soft soils.