Fatigue assessment framework for steel-concrete-composite bridges considering component-degradation and corrosion coupled effects

Existing fatigue assessments of steel-concrete composite girder bridges often neglect the critical interaction between vehicle-induced degradation and environmental corrosion. To address this limitation, this study introduces a comprehensive life-cycle framework designed to elucidate the fatigue damage evolution under these coupled actions. A vehicle-bridge coupled vibration system was first established, in which the vehicle and bridge model were determined based on the AASHTO bridge design specifications. Subsequently, corrosion and degradation models for key structural elements, including road surface condition (RSC), concrete deck, and steel girders, were developed. Building on this foundation, a time-dependent fatigue analysis framework was proposed, which iteratively updates the finite element model based on the coupled system's dynamic responses to capture the synergistic effects of corrosion and vehicle-induced degradation. The results demonstrate that the coupled action induces a severe synergistic acceleration of fatigue damage accumulation ( FDA ) and reduces bridge service time by at least 45% compared to individual action. Furthermore, the analysis reveals the competing mechanism of component degradation on the stress range and thus on the fatigue damage accumulation of fatigue details. These findings highlight the imperative to integrate coupled mechanical-environmental degradation into fatigue design and maintenance strategies to ensure long-term structural safety and serviceability.