Structural Safety Evaluation of Multi-Storey Car Parks in Major Nigerian Cities: A Focus on Kano and Lagos

Multi-storey car parks present unique structural engineering challenges due to their exposure to moving vehicular loads, open facades exposing reinforcement to chloride-laden air, and the use of flat or post-tensioned slabs over large column-free spans. This study evaluates the structural safety of six multi-storey car park structures across Kano in the North West and Lagos in the South West geopolitical zones, assessing compliance with current design standards and identifying deficiencies requiring intervention. The evaluation incorporated visual inspection of structural elements, chloride content testing of concrete from outer column faces and slab soffits, carbonation depth measurement, and review of original structural calculations where available. Results indicate that four of the six car parks exhibited chloride-induced reinforcement corrosion at or above the initiation threshold, with the highest chloride contents recorded in the open-deck perimeter columns of the two Lagos facilities, consistent with coastal airborne chloride exposure. Carbonation depths exceeded cover depths in reinforcement at lower deck levels in three structures, predicting ongoing corrosion progression without intervention. One Kano facility showed extensive diagonal cracking at column heads indicative of punching shear distress under heavy vehicle concentration. Structural safety ratings using the Institution of Structural Engineers Car Park Guidance Note criteria classified two car parks as requiring immediate investigation and potential load restriction. Recommendations include the installation of impressed current cathodic protection on the most corrosion-affected structures, load restriction pending full structural assessment, and a national protocol for periodic car park structural safety inspection. Keywords: multi-storey car parks, structural safety, chloride, corrosion, punching shear.