Analytical Investigation of Fatigue Behavior in a Modified Composite Steel Box Concrete Girder Bridge with Corrugated Steel Webs under Pavement and Expansion Joint Deterioration

In this study, the numerical investigation of the fatigue impact factor of critical structural details near the expansion joint for a modified composite steel box concrete girder bridge with corrugated steel webs (MCSBCGBCSW) was conducted using a vehicle–bridge coupled vibration system (VBCVS). Within the VBCVS framework, the MCSBCGBCSW served as the bridge model, and the three-axle vehicle model was employed as the fatigue vehicle loading model. Additionally, deterioration models for pavement roughness and expansion joints were established. The stress impact coefficient IMS and stress amplitude impact coefficient IMR of critical structural details near the expansion joint were investigated in detail, considering various vehicle speeds, pavement roughness conditions (PRCs), and expansion joint deterioration degrees (EJDDs). The results demonstrate that the most critical factor affecting IMS and IMR of the critical structural details near the expansion joint is the deterioration degree of the PRC rather than the vehicle speed or EJDD, with maximum values of 4.943 and 8.682, respectively, when the PRC is very poor. When the distance between the critical structural details and the expansion joint is within 6 m, a greater dynamic impact action is observed, with a maximum value of 4.067. The fluctuation range of IMR between the critical structural details decreases and stabilizes as the distance between these details and the expansion joint exceeds 6 m. Based on the IMR of the critical structural details near the expansion joint, a calculation formula for the design value of IMR was developed for an MCSBCGBCSW, with a confidence level of 95% compared to the values stipulated by the American Association of State Highway and Transportation Officials specification. These results provide reference information for calculating the IMR of the critical structural details near expansion joints for MCSBCGBCSWs.