The seismic resistance of reinforced concrete building aggregates of high building unit plan slenderness ratio with soft storey basements on clay subsoil

Abstract

The construction industry in Malta has remained quite traditional. There have been advances in building construction methods, which, however, have not yet been widely implemented. The most common system is the masonry wall system with an overlying slab. Throughout the years, the local building stock has witnessed an increase in building heights, particularly within town and village centres, where the predominant building typology is the unreinforced masonry (URM) load-bearing building with an open plan soft storey basement used primarily for car parking. Buildings are being demolished to make space for larger structures and to increase the space obtained. As the number of floors constructed above ground within these buildings increases, so does the resulting accommodation space. The population is opting for open plan internal areas with minimal vertical load-bearing obstacles in order to increase the flexibility and flow of the space. Basements and garages are constructed using piers or columns rather than walls so as to increase the spaces provided, but often the columns over basement level do not act rigidly with the slab, thereby leading to the creation of a “Soft Storey”. When looking at the lateral stability of these load-bearing structures, all the aforementioned effects drastically reduce the lateral stability of the buildings, due to fewer walls acting continuously along the height of the building. Through the introduction of reinforced concrete (either in situ or precast twin wall construction) as the main material of wall construction, a certain level of continuity may be achieved, certainly much greater than can possibly be obtained with masonry wall construction. Furthermore, the increasing heights of buildings for the same building plot width results in an ever-increasing Slenderness (Height-toWidth) Ratio. Several research studies have been carried out with regards to seismic resistance of masonry structures, although none of the previous studies considered the effect of using reinforced concrete walls instead of masonry walls. The results obtained from this dissertation have shown that, by utilizing reinforced concrete rather than masonry wall construction in building aggregate systems, a better degree of continuity would be obtained between the slabs and walls, thereby leading to enhanced structural performance and seismic resistance. This dissertation aims to achieve a better understanding of the seismic resistance and seismic vulnerability when using reinforced concrete walls rather than masonry walls within building aggregates of high slenderness ratios with soft storey basements.