Field testing and finite element modelling of old metal railway bridges with corrosion impact analysis

Bridges are vital to transport infrastructure and connectivity, but old bridges pose significant maintenance and possibly even safety concerns. Accurately assessing the structural health of old bridges requires an approach that accounts for both bridge conditions and detailed simulation. This paper describes field monitoring and associated numerical investigation to assess the impact of corrosion on the structural performance of two old steel railway bridges, with an emphasis on nonlinear behaviour. Measured structural accelerations (natural frequencies of 13.9 Hz for bridge 1 and 7.2 Hz for bridge 2) and deflections during train passage are used to verify the accuracy of finite element models of each bridge in capturing modal responses and deflection behaviour. Parametric analyses across multiple corrosion scenarios for both representative bridges showed that a uniform thickness loss of around 30 % resulted in only a 10–12 % decrease in natural frequency and a 40–73 % increase in deflection (less than 1.5 mm) but led to substantial stress increases of up to 60–180 %. This demonstrates that stress is significantly more sensitive to corrosion than global stiffness or frequency. Moreover, localised corrosion produced far greater stress amplification than uniform corrosion with comparable total mass loss, confirming its potential to cause local yielding even when global deflection remains within acceptable limits. The study establishes a validated framework combining field measurements with corrosion-sensitive FE modelling to quantify the impact of both uniform and localised corrosion on old bridges. The findings highlight the need to integrate global monitoring data with detailed local inspections and modelling to improve the accuracy of bridge condition assessment and long-term service life prediction.