Influence of structural-geological features and knowledge levels on the seismic vulnerability of masonry clustered buildings: a case study in Mirandola (Italy)

Unreinforced masonry clustered buildings constitute a significant portion of Italy’s existing building stock, particularly in historic city centres, which resulted from unplanned and non-engineered urban development over centuries. In most cases, the individual structural units within an aggregate were built in different time periods, without connections to pre-existing units and often with different materials. Seismic vulnerability assessment of masonry aggregates presents a major challenge in engineering, due to the difficulty of obtaining comprehensive geometric and structural data for each individual cell. This paper presents a parametric analysis of a typical masonry clustered building located in Mirandola, in the province of Modena, Emilia-Romagna. The region was severely affected by the May 2012 earthquake, which caused widespread damage to the urban fabric of Mirandola, destroying several structures and resulting in numerous fatalities. An aggregate from the historic centre of Mirandola was selected for non-linear analyses, varying different parameters. Initially, the effects of three knowledge levels, as outlined by the Italian Technical Code, were assessed. In the second stage, the structural characteristics were varied by changing the type of masonry (regular or irregular). Finally, the impact of the stratigraphical soil category was examined. Following the analyses, fragility curves were plotted to assess which parameter had the most detrimental impact on the seismic behaviour of the complex. The findings indicate that lower knowledge levels heighten uncertainty, irregular stone masonry increases vulnerability, and softer soils amplify seismic effects. This study, a unique contribution to the field due to the limited availability of parametric analyses on these factors, underscores the importance of precise material characterization and targeted reinforcement to enhance the seismic resilience of historic masonry aggregates.