Distortion-Induced Fatigue Mechanism and Lane-Distribution-Based Damage Assessment of Steel Plate Girder Bridges

Distortion-induced fatigue is an important failure mechanism in steel plate girder bridges. Existing studies have advanced the understanding of local stress responses and damage identification of distortion-sensitive details; however, the mechanism by which traffic lane distribution affects distortion-induced fatigue characteristics and governs fatigue damage accumulation remains insufficiently understood. To address this issue, a global–local finite element model was established using ABAQUS 2016 to investigate deformation transfer behavior and fatigue stress responses in a steel plate girder bridge. Longitudinal and transverse load position analyses were conducted to quantify the spatial characteristics of fatigue responses. Furthermore, a lane-distribution-based fatigue damage assessment framework was developed and verified. The results demonstrated that distortion-induced fatigue response is governed by deformation incompatibility, with web gap welds identified as the critical fatigue details under different structural configurations. The transverse displacement at the stiffener end showed a strong correlation with fatigue stress (Spearman coefficients > 0.8). The transverse influence range extended across almost the entire region between the two main girders, indicating that adjacent-lane loads contribute to fatigue damage accumulation. Compared with the single-lane critical load method, the proposed framework better represents fatigue damage evolution under actual lane distributions and captures asymmetric damage between the two girders, with the maximum difference reaching 46.7%. This study provides new insights into distortion-induced fatigue evolution from the perspective of traffic lane characteristics and offers a refined approach for fatigue assessment of existing steel plate girder bridges.