Structural Assessment of Selected Aging Bridges on Federal Roads in Ogun State

Nigeria's federal road network includes numerous aging bridge structures that have not received systematic structural assessment, creating potential safety risks for road users. This study conducts a visual and non-destructive structural assessment of five selected bridges along federal road corridors in Ogun State, South West Nigeria. A visual inspection protocol based on the Federal Highway Administration bridge inspection manual was applied, supplemented by rebound hammer testing for in-situ concrete strength estimation and crack mapping. Bridge element condition ratings were assigned using a modified Nigerian Federal Ministry of Works grading scale. Structural adequacy was assessed by comparing estimated load capacity with current commercial vehicle loading requirements. Results indicate that two of five assessed bridges are in poor condition (Overall Condition Rating below 4), with significant concrete spalling exposing corroded reinforcement in the deck and abutments. Rebound hammer estimates suggest in-situ concrete compressive strengths between 12 and 18 MPa in deteriorated zones, below the design minimum of 25 MPa. Crack widths exceeding 0.5 mm were recorded at midspan soffit locations on two bridges. The study concludes that immediate structural intervention is required for two bridges and that routine inspection protocols should be established for all highway bridges in Ogun State. Recommendations include load posting restrictions and priority placement on the Federal Roads Maintenance Agency rehabilitation programme.

Keywords: bridge assessment, structural condition, aging infrastructure, Ogun State, federal roads