Influence of structural unit-interconnection degree on the seismic response of unreinforced masonry building aggregates

Unreinforced aggregate buildings are the result of progressive expansion across different construction periods, leading to heterogeneous structures composed of multiple units with varying degrees of connection. These connections are often complex to identify and even more challenging to model. This study investigates the impact of the different interconnection degree to the seismic response and damage evolution of masonry aggregates through an explicit modelling of the inter-unit connectivity. A three-structural unit elementary building aggregate is analyzed by simulating nonlinear time-history analyses under two assumptions for the slab (flexible and a rigid diaphragm) and three different semi-connection degrees besides the isolated and fully connected cases. The effects are evaluated in terms of displacement and base shear demand, energy dissipation and damage distribution over the longitudinal walls. The finite element (FE) model is developed using a continuum homogenized modeling approach for the masonry walls and the interfaces with 2D layered shell elements. The results show that stronger inter-unit connections lead to better performance of the structural units and markedly reduced in-plane damage, exhibiting displacement demands up to three times lower than the isolated units. However, the results also show that modelling units as isolated structures is not always conservative, with the external units experiencing increased displacement demand especially in the cases of weak connections and flexible diaphragms.