Mechanical Deterioration of Q420 Bridge Steel in Dual-Corrosive Environments

The mechanical degradation of Q420 bridge steel in arid, deicing-salt environments poses a major threat to structural integrity and economy. This study combines experimental and numerical analysis to elucidate the fracture mechanism under combined atmospheric and salt corrosion. Specimens exposed for 0–60 days underwent quasistatic tensile tests and scanning electron microscope fracture analysis, revealing three decisive pit types. These findings directly guided the development of three finite element models, including a uniform corrosion model and models with explicit pit geometries. Results showed post-60-day corrosion elevated stress concentrations by over 33%. The modified void growth and stress-weighted damage models, incorporating these pitting parameters, achieved fracture displacement predictions with ≤ 6 % error, validating their accuracy as representations of the fracture process. This integrated approach not only shifts the failure analysis paradigm from conservative uniform-corrosion assumptions to morphology-aware prediction but also provides engineers with validated tools for quantitative residual life assessment.