Analysis of Floor Slab Deflection in Multi-Storey Commercial Buildings in Abuja’s Central Business District

Excessive floor slab deflection in multi-storey commercial buildings poses risks to serviceability, finishes integrity, and occupant confidence, particularly in high-density urban environments. This study analyses floor slab deflection behaviour in selected multi-storey commercial buildings within Abuja's Central Business District in the North Central geopolitical zone, focusing on flat slab systems constructed between 2015 and 2022. Deflection measurements were taken using a precision optical level at ten reference points per floor across eight buildings, and the readings were compared against the allowable limits prescribed by Eurocode 2 and the Nigerian National Building Code. Construction drawings were also reviewed to assess compliance with span-to-depth ratios and shear reinforcement detailing. Findings reveal that three of the eight buildings exhibited total long-term deflections exceeding span/250, the threshold above which damage to non-structural partitions is expected. Inadequate attention to creep and shrinkage effects during the design stage was identified as the principal cause, compounded by early striking of formwork before concrete achieved its full design strength. Cracks at column-slab interfaces consistent with punching shear initiation were observed in one building, warranting urgent structural assessment. The study recommends the adoption of long-term deflection monitoring using embedded sensors during construction and the strict enforcement of minimum curing periods before striking flat slab formwork. Keywords: flat slab, deflection, multi-storey buildings, Abuja, serviceability.