Effects of weld residual stress and relaxation on fatigue life of rib-to-deck joint in orthotropic steel deck

Fatigue cracking frequently manifests at the rib-to-deck (RTD) joints of orthotropic steel decks (OSDs) in steel bridges. Welding residual stress (WRS) and its subsequent relaxation (WRSR) constitute primary factors that undermine fatigue resistance and jeopardize structural integrity. Neglecting the synergistic effects of WRS and WRSR in fatigue assessments may result in significant inaccuracies. This study investigates the influence of initial WRS and WRSR on fatigue life through a fracture mechanics-based approach. Specifically, the initial WRS and its relaxation under external cyclic loading were simulated using a three-dimensional thermo-mechanical model and a macroscopic time-independent plastic constitutive model, respectively. These models were validated against experimental data and integrated into a crack propagation model to predict fatigue life. By accounting for both WRS and WRSR, the proposed model yields fatigue life predictions with a relative error of merely 2.7% compared to test data. In contrast, neglecting both WRS and WRSR leads to an overestimation of fatigue life by 12.3%, while considering WRS without accounting for WRSR results in a 10.3% underestimation. Furthermore, the impacts of stress amplitudes and stress ratio on fatigue life were examined, revealing a negative correlation. Ultimately, a predictive formula was derived as a function of stress amplitude and stress ratio. The results demonstrate that the formula-based predictions align closely with the simulation data, achieving a coefficient of determination (R 2 ) of 0.98, which underscores the high predictive accuracy of the proposed formula.