Modelling of unreinforced masonry churches: analysis and reduction of their seismic vulnerability

Churches are a significant portion of the religious, historical and artistic heritage of many countries worldwide. When such countries present a moderate to marked seismic hazard, damage can be frequently observed (Brandonisio et al., 2013), (S. Lagomarsino & Podestà, 2004a), (Marotta et al., 2017), (Penna et al., 2019a), (Sorrentino et al., 2014). The seismic behavior of churches can be assessed resorting to models of different complexity and computational burden. The Italian guidelines for the assessment and the reduction of the seismic risk of heritage constructions (DPCM, 2011) allow for a statistical assessment based on vulnerability modifiers (S. Lagomarsino & Podestà, 2004b) or for the extensive analyses of local collapse mechanisms (Borri et al., 2019) or for the implementation of more complex global models (Bertolesi et al., 2018), (Jain et al., 2020), (Mendes et al., 2020), (Pantò et al., 2016). The third approach is of course the most challenging but removes the need for conventional assumptions about predetermined responses and distribution of loads between macroelements. This thesis aims to investigate the seismic vulnerability of Italian churches. It will analyze the structural characteristics that make them prone to collapse during earthquakes, review past damages as lessons for present practice, explore methodologies for their protection and strengthening end advance the seismic understanding of Italian churches. Furthermore, a study was conducted on the modeling and verification of the Troia Cathedral (Foggia). The seismic response of the aggregate was studied with reference to local collapse mechanisms, both in terms of force and displacement, taking into account the capacity limitations posed by horizontal transverse structures, such as floors and vaults. Given the presence of squared stone block masonry, the contribution of frictional clamping was modeled. To perform a seismic vulnerability assessment, a procedure was implemented to create a three-dimensional numerical model based on available documentation, using finite element (FE) modeling and adopting a damage model for the masonry. The procedure involved the use of various software programs: AUTOCAD, RHINOCEROS, GRASSHOPPER, and FEAP, which allowed for the processing of input data and the generation of an optimized FE numerical model designed for performing nonlinear, static, and dynamic analyses. In parallel, with the aim of obtaining representative geometries useful for creating a prototype church, work was carried out by applying the "2020 Church Cartis Sheet", integrated with additional fields, to a collection of 108 churches located in different Italian regions in zone 1 or zone 2 according to the OPCM (2005), the two areas with the highest seismicity according to Italian building codes. The resulting masonry church prototype was, in a first phase, modeled and analyzed in its unreinforced condition using both modal analysis, to investigate the structure's dynamic characteristics, and pushover analysis, to evaluate its nonlinear seismic performance and collapse mechanisms. These results provided valuable insights into the intrinsic weaknesses and collapse modes of the building in its original state. In a second phase, intervention strategies aimed at improving the seismic resilience of the church prototype were applied to the model. Modal and pushover analyses were repeated on the same numerical model, incorporating these interventions, with the aim of quantifying their contribution in terms of changes in dynamic properties, improved load-bearing capacity, and reduced seismic vulnerability.