The Italian Guidelines for the seismic risk assessment of cultural heritage. The illustrative case study of the Basilica of San Francesco in Arezzo

The paper, through the discussion of the illustrative case study of the Basilica of San Francesco in Arezzo (Italy), summarizes the methodology of seismic risk assessment proposed by the Italian “Guidelines for the assessment and mitigation of the seismic risk of the cultural heritage” (DPCM 2011) [1]. The Basilica was investigated within a research project promoted by the Italian MIBACT and financed by ARCUS SpA and, in a first part, the paper reports about the knowledge process performed to characterize the geometric and mechanical parameters required for a reliable structural analysis. Subsequently, the methodology of analysis proposed by the Italian Guidelines, based on three increasing levels of knowledge of the structure, is discussed. The first level of analysis (LV1) allows to evaluate the collapse acceleration of the structure by means of simplified models based on a limited number of geometrical and mechanical parameters. The second level (LV2) is based on a kinematic approach performed to analyse the local collapse mechanisms that can develop on several macroelements. The last level of evaluation (LV3) requires a global analysis of the whole building under seismic loading by suitable numerical models. To perform the global analysis (LV3) the finite element modelling technique was employed, and the seismic capacity was evaluated through a pushover approach. Evaluating the capacity of the Basilica to horizontal, the paper critically discusses the employability of pushover global analysis for the seismic assessment of Basilica-type churches.