Seismic vulnerablity and strengthening of a masonry building aggregate. A case study in Prata (L'Aquila)

Masonry building aggregates constitute a significant portion of the Italian architectural heritage. This building typology comprises adjacent structures, often constructed in different historical periods and therefore featuring significant differences in materials and construction techniques. The temporal layering of these buildings has led to structural heterogeneity, with connections between individual units that may be more or less effective, resulting in a lack of overall structural unity. This complexity makes building aggregates vulnerable to collapse mechanisms when subjected to seismic forces, especially due to irregular interactions between different parts. This study focuses on a specific case of a masonry building aggregate located in Prata (Lucoli, L’Aquila), which sustained significant damage during the 2009 L’Aquila earthquake. Following the seismic event, widespread cracks and separations between walls and inadequately anchored floors were observed, with damage particularly concentrated in the central area of the aggregate. To assess the seismic vulnerability of the structure, software 3Muri was used. Nonlinear static analyses were performed to evaluate the global load-bearing capacity of the model, as well as kinematic analyses to examine and verify local failure mechanisms. These analyses revealed significant vulnerability of the structure to horizontal loads, showing how seismic action can easily activate local collapse mechanisms in the absence of adequate structural connections. The results provided a basis for the design of targeted strengthening interventions to improve the overall structural resistance and reduce the seismic vulnerability of the aggregate.