Damage‐Based Fatigue Assessment of K‐Type Cast Steel Joints Considering Welding Residual Stresses and Casting Defects

Cast steel joints in steel truss bridges are vulnerable to fatigue damage due to welding residual stresses and casting defects. This study develops a damage‐based framework that incorporates welding residual stresses and defect‐induced initial damage into an atomic thermal perturbation damage model. Model parameters for ZG300‐500H cast steel and Q345qD steel were calibrated using high‐cycle fatigue tests and literature data, and the model was applied to a K‐type cast steel joint with an asymmetric circumferential butt weld and internal porosity defects. Increasing axle weight reduced the predicted fatigue life from 2.19 × 10 6 to 6.3 × 10 5 cycles, with each 10‐kN increase causing a 33%–35% reduction. Welding residual stresses reduced fatigue life on the cast steel side by 56.3%, while porosity defects caused reductions of up to 82.5%. These results highlight the need to consider residual stresses and initial defects in fatigue life assessment of cast steel joints.