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. The seismic behavior of churches can be assessed resorting to models of different complexity and computational burden. The 2011 Italian guidelines for the assessment and the reduction of the seismic risk of heritage constructions allow for a statistical assessment based on vulnerability modifiers or for the extensive analyses of local collapse mechanisms or for the implementation of more complex global models. The third approach is of course the most challenging but removes the need for conventional assumptions about predetermined responses and distribution of loads between macro-elements. This thesis aims to investigate the seismic vulnerability of Italian churches. It will analyse the structural characteristics that make them prone to collapse during earthquakes, review existing literature about experiments and intervention techniques. With the aim of obtaining representative geometries useful for creating a prototype church, the CarTiS church form, integrated with additional fields, was applied to a collection of 108 churches located in the highest seismicity areas according to the Italian building code. The resulting masonry church prototype was, in a first phase, modeled and analyzed in its as-built condition using both modal analysis, to investigate the structure dynamic characteristics, and pushover analysis, to evaluate its nonlinear seismic performance and collapse mechanisms. To perform the assessment, a procedure was implemented to create a three-dimensional numerical model, within the finite element method and adopting a damage model for the masonry implemented in FEAP. These results provided valuable insights into the intrinsic weaknesses and collapse modes of the building in its original state. In parallel, the modeling and verification of the Cathedral of Troia (Foggia) was performed, taking advantage of in situ survey and testing. Finally, intervention strategies (such roof stiffening and buttresses addition) aimed at improving the seismic performance of the prototype church were applied to the model. Modal and pushover analyses were repeated in the post-intervention condition, with the aim of quantifying their contribution in terms of changes in dynamic properties, improved load-bearing capacity, and reduced seismic vulnerability.