Seismic retrofitting of local contemporary unreinforced masonry buildings with soft storey basements constructed using hollow concrete blockwork

Abstract

URM Buildings in the Maltese Islands have been traditionally designed without taking into regard loading by earthquake activity. Consequently, some concerns have been raised by local experts over the last few decades regarding the increase in construction of unreinforced masonry-load bearing buildings built out of hollow concrete blockwork having a clear-span basement in the Maltese Islands. The reason is that such buildings are highly vulnerable to earthquakes, due to the soft storey effect created at the basement level. The research methodology used in this dissertation consisted of a numerical approach where 3D Macro was used to carry out a non-linear static pushover analysis. The objective was to determine the number of additional floors that a URM building can support once the structure has been retrofitted with sway resistant frames using either reinforced concrete or structural steelwork plane frames in the basement level where several factors come into play such as the aggregate size and ground type. At the same time, the seismic vulnerability of the retrofitted URM buildings is being assessed and compared with the seismic vulnerability of the URM buildings with soft storey basements and repeated ground floor arrangements. Throughout the analysis, it was acknowledged that assessing and comparing the seismic vulnerability of different URM buildings by the number of floors supported does not reflect their true seismic behaviour. Instead, the safety factors which are also known as alpha values give a better understanding of the seismic performance of the buildings analysed. Key observations from the results include the effectiveness of retrofitting portal frames in structural steel which proved to be the best solution to increase the seismic resistance of the URM buildings with soft storey basements. The effect of the enhancement of the retrofitting structures was shown mostly on Ground Type A (rock), the strongest ground material taken for this study. Also, as the aggregate size increased so did the seismic resistance of URM buildings on Ground Type A meaning that the increase in the rate of sway resistance is larger than the increase in the rate of the seismic mass.