Structural assessment of the seismic sway resistance of local unreinforced masonry building aggregates with discontinuous internal masonry partition walls

Abstract

The built environment of the Maltese Islands is saturated with buildings constructed using unreinforced masonry (URM). This construction practice relies heavily on the skill of the mason, and, therefore, such buildings are rarely designed to comply with codes of practice. Furthermore, the last recorded earthquake which caused significant damage in the Maltese Islands occurred in 1693 and, therefore, the local population does not generally view earthquakes as a particular hazard. However, in recent years, an interest has developed in the performance of local URM buildings under earthquake loading and studies have shown that the building heights regulations which are currently in place, could render URM buildings unsafe. Nevertheless, it was also concluded that when individual buildings units are situated within an urban building aggregate, which is the norm, they could also experience an enhanced performance in resisting seismic loading. This parametric study was carried out using the Equivalent Frame Method and it seeks to take this research topic a step further, into a more realistic scenario, where the internal transverse partition walls of adjacent building units forming a building aggregate are not perfectly aligned. The effect of having a displacement in the longitudinal direction of 20% of the plot width of the individual building units, upon the safe height of the building aggregates subjected to seismic loading, was investigated for various plan configurations of building aggregates, with varying combinations of mortar type, ground geotechnical type and building material type. Through the structural analysis performed, it was concluded that such building aggregates achieved a marginal increase in the seismic resistance when compared to building aggregates with continuous internal transverse partition walls. However, the building heights as currently prescribed in L.N. 227 of 2016 still remain unsafe for the majority of cases considered in this study.