Structural Health Monitoring of a Selected Reinforced Concrete Highway Bridge in Ogun State Using Vibration-Based Techniques

Vibration-based structural health monitoring provides a non-invasive means of detecting changes in the dynamic characteristics of bridges that indicate structural degradation, stiffness loss, or damage accumulation before visible symptoms appear. This study implements a vibration-based structural health monitoring system on a selected reinforced concrete highway bridge on the Lagos-Seme coastal expressway in Ogun State in the South West geopolitical zone, a bridge of significant strategic importance to West Africa's coastal trade corridor. Piezoelectric accelerometers were installed at nineteen locations on the bridge deck, piers, and abutments, and ambient vibration data were recorded over twelve months under operational traffic. Operational modal analysis using the stochastic subspace identification method was applied to extract natural frequencies, mode shapes, and damping ratios from ambient vibration records. Baseline modal parameters were established and deviation from baseline tracked as a damage-sensitive feature. Damage scenarios including simulated column stiffness reduction and additional mass were introduced computationally to validate the sensitivity of identified modal features to realistic damage states. Results indicate that natural frequencies were identified with a coefficient of variation below 3 percent across repeated measurement sessions, confirming system consistency. A 15 percent reduction in column-bending stiffness was detectable as a 4.2 percent frequency shift, above the noise threshold of the monitoring system. Long-term seasonal temperature effects produced modal parameter variations that required compensation to avoid false damage indications. The study provides a replicable structural health monitoring framework for Nigerian highway bridges and recommends its adoption in the Federal Ministry of Works bridge monitoring programme. Keywords: structural health monitoring, vibration-based, highway bridge, operational modal analysis, Ogun State.