AbstractThe linear elastic fracture mechanics (LEFM)–based approach has been widely applied to investigate the threshold for corrosion-to-fatigue crack transition in the corrosion fatigue process. However, investigations to determine the transition threshold of generally corroded steel are still insufficient. In the present study, the threshold for the corrosion-to-fatigue crack transition was investigated via fatigue testing of naturally corroded steel plates. The specimens were procured from the corroded U-ribs obtained from a cable-stayed bridge that has been in operation for more than 30 years. Profiles of the corroded surface were obtained via three-dimensional scanning. Stress intensity factor ranges and stress concentration factors were examined as potential indicators of a threshold for corrosion-to-fatigue crack transition. These factors, however, proved to be inappropriate. Modified stress intensity factor range was proposed to consider the shape-dependent effect of stress concentration from corrosion damage, and a consistent threshold of corrosion-to-fatigue crack transition was identified. These results are a novel finding whereby the corrosion-to-fatigue crack transition could occur when the modified stress intensity factor range exceeds 600 MPa√mm.