Structural Consideration in Design of Reinforced Concrete Slabs with Openings

Over 90% of framed structures in Uganda are built from reinforced concrete. Prior to the 1990’s, most buildings had no openings in slabs, yet in city centers buildings butt against each other with widows at front and back only. This limited retail activities to front rooms of the ground floor and the buildings had to be narrow. A baseline survey of 50 shopping malls in Kampala Central Business District revealed that 40 of them have openings through all floors to the transparent roof section above. These openings allow improved air circulation and lighting, and facilitate full utilization of the structure for retail up to the last floor. However, the openings pose a break in the continuity of the slab; a potential weak point in the whole structure. Reinforced concrete slabs with openings are usually designed with help of traditional rules of thumb proposed by building codes. Such methods however, introduce limitations concerning size of openings and magnitude of applied loads. The research investigated the current methods of analysis and design of reinforced concrete slabs with openings. Approved plans were obtained and analyzed with emphasis on detailing. The problem is compounded when openings are made in existing slabs; strengthening methods for the slab are explored. The seismic performance, shortfalls in design and detailing methods of slabs with holes are explained.