Modelling strategies for structural units within masonry aggregates

Many historic centers in Italy are composed of masonry aggregates—clusters of adjoining buildings developed over time. Within these aggregates, it is often possible to identify structural units (S.U.s), which represent the smallest portions with potential for independent structural behavior. When retrofitting interventions are required, it is essential to correctly define the extent of the intervention unit and understand how to model it accurately, without the need to simulate the entire aggregate. In this study, a case located in Todi (Italy), specifically the north-east corner of a school building, is investigated as a representative S.U. within a masonry aggregate. Based on historical and structural analysis, the S.U. is modeled in three different configurations, with varying extents of adjacent portions included. The goal is to evaluate the extent of the surrounding aggregate that has to be modeled to reliably reproduce the S.U.’s seismic behavior. Results are evaluated through capacity curves and validated against damage patterns observed on site. The analysis confirms that including a limited extent of the adjacent buildings is sufficient to significantly improve the accuracy of the structural model, particularly in terms of stiffness and damage distribution. The model shows a notable increase in capacity, confirming the effectiveness of the proposed modelling strategies.