Seismic response of unreinforced masonry building aggregates: Investigation on the “aggregate-effect” based on an elementary building aggregate

Masonry building aggregates constitute a significant portion of Italian and Mediterranean countries built heritage. These structures originate from the progressive transformation and interconnection of originally isolated structural units over time. Masonry aggregate seismic performance is affected by significant uncertainty arising from the lack of knowledge of their complex structural arrangement, which is also reflected in the reliability of modeling assumption adopted for the analysis and the descending outcomes. This paper presents a numerical study investigating the seismic behavior of an elementary building aggregate made of three almost identical structural units. Different boundary conditions are explored in the analysis, extracting and comparing the responses of the individual structural units modeled both in aggregate and isolated and with rigid or flexible floors. Homogenized masonry approach is implemented for the building aggregate models with 2D layered inelastic shell elements. The structural models are realized with the STKO software platform for OpenSees, enabling parallel computing to analyze large scale models. Results will highlight the extent of the so-called "aggregate effect" for the elementary aggregate building and its potential benefits to the structural units, showing also that the behavior of structural units in aggregate strongly depends on their position and the polarity of the seismic forces.