Seismic Vulnerability Assessment of a Building Aggregate in the Historical Centre of Florence

Safeguarding the built heritage represents an urgent challenge for the culture and identity of each country. In Italy, past seismic events have highlighted the vulnerability of historic urban centres, as aggregates of historic masonry buildings. In this work, the seismic vulnerability of the historic centre of Florence, a UNESCO heritage site since 1982, will be investigated in the context of the Vulnerability Index Method, an empirical approach for the vulnerability assessment at the territorial level, proposed by Benedetti and Petrini in 1984, adopted by the Italian Group of Defense from Earthquake in 1993 and integrated by Formisano in 2011 with the key factors linked to the influence of the aggregate layout in the seismic behaviour. In particular, an urban aggregate composed of fourteen masonry in-line buildings (two palaces in the corner and twelve serial intercluded buildings) is considered as a case study. Buildings show a long narrow plan and an internal court and have undergone many transformations throughout history. Historical and typological analysis and material and constructive investigations were carried out to aid in understanding the mechanical behaviour of these buildings. These preliminary analyses allowed us to highlight the specific features and vulnerabilities of the aggregate, such as the presence of an internal court, which was the object of a specific study carried out supported by non-linear FEM investigations. In particular, this study was aimed at understanding how the GNDT form of the Seismic Vulnerability Level II can describe the vulnerability induced by the internal court in the seismic behaviour of the typical historical buildings in the city centre of Florence. First, the parameters of the GNDT form, influenced by the internal court, have been identified. Some considerations are reported by evaluating the results relating to these parameters, obtained for the application of the case study. Subsequently, some possible proposals for integrating the GNDT form were formulated to include the local vulnerability induced by the internal court in the structural behaviour of the typical historical buildings of the UNESCO city centre of Florence.