Moving-train-induced rotation and multi-crack propagation analysis for pinned suspender of suspension bridges

The frequent longitudinal repetitive motion induced by asymmetric train loading accelerates the deterioration of ‌suspenders of suspension bridges. A friction-based rotation capability model ‌was established based on restricted rotation analysis at the pinned ‌suspender anchorage, deriving formulas for the rotation-triggered longitudinal incline threshold‌ and moving-train-induced bending moment. Based on an actual ‌suspender fracture incident in a self-anchored ‌rail transit suspension bridge‌, a multi-scale fatigue crack propagation model was established for the ‌pinned anchorage‌ of short ‌suspenders‌. The results showed that, restricted rotation causes a maximum nominal bending stress of 130 MPa at short suspender anchorages, with peak nominal stress hitting 232.9 MPa. Bending stress constitutes over 50% of total stress in fatigue-prone sections. 70% of the train’s design axle weight is recommended as the fatigue load model for rail transit bridges. The unfavourable bending stress range at the upper anchorage threads’ fatigue-prone detail reaches 182 MPa, while axial tensile fatigue stress range stays below 6 MPa. Both the fracture morphology observation and crack propagation analysis reveal that multi-crack propagation under bending stress is the fundamental driver of fatigue fracture in the suspender anchorage.