Fragility functions of unreinforced masonry aggregate buildings under varying unit-interconnectivity conditions

Within the Mediterranean region, particularly in Italy, masonry aggregate buildings constitute a significant portion of the architectural heritage. These structures result from the gradual transformation and interconnection of originally isolated structural units over time, shaping the evolution of urban areas. Assessing the seismic performance of masonry aggregates is challenging due to the significant uncertainties arising from interactions between individual units. Moreover, existing building codes and standards lack comprehensive guidance on this topic, impacting the reliability of modeling assumptions and the accuracy of analytical outcomes. Consequently, studying masonry aggregates at an elementary level, with similar regular units, to isolate the effects of unit interconnectivity has recently gained interest. This thesis is structured into two parts. The first part presents a fragility analysis of a reference building aggregate composed of three similar structural units, evaluated under three different boundary conditions: (i) in-aggregate configuration with a rigid connection between units, (ii) in-aggregate configuration with a degrading connection, and (iii) as isolated buildings. The probability of exceeding the collapse limit state is estimated using the in-plane drift on masonry panels as the engineering demand parameter (EDP), measured during an Incremental Dynamic Analysis (IDA) with a set of thirty ground motions. The second part applies the lessons learned to a real case study—the Palazzo Ducale of Popoli (Pescara)—for which a detailed numerical model was created to study its dynamic behavior, considering the building as part of a more complex architectural arrangement. The presence of adjacent structures was simulated by introducing constraints. The building was assessed using the previous framework with a reduced number of ground motions due to the large scale of the structure. All numerical models are developed using the STKO software platform for OpenSees, enabling parallel computing for large-scale analyses. A homogenized masonry approach is adopted, employing 2D layered inelastic shell elements. The results showcase the impact of the so-called “aggregate effect” and its potential benefits for the seismic performance of individual structural units. They also emphasize the critical influence of boundary condition modeling choices on the evolution of global and local failure mechanisms.