This study aimed to investigate the effect of the fatigue life enhancement of the rib-to-deck welded joints of orthotropic steel decks (OSDs) by extended peening treatment utilization. First, hammer peening was conducted around the weld bead of the test specimens of OSDs. It was found that the treatment on both the weld toes of the deck and the U-rib plates caused a deformation of the U-rib plate, i.e., peen forming. Then, fatigue tests were performed under R = 0.0, using an out-of-plane bending fatigue test machine by applying several magnitudes of pre-loadings, and the results showed that the specimens with peen forming had one JSSC class higher than the deck plate only. Finally, numerical simulations of peening treatment and peen forming were performed to reveal the reason for higher fatigue life enhancement by peen forming. Simulation results showed that peen forming would introduce about three times higher compressive residual stress at the weld root of the deck plate side than the peening treatment on the deck plate only, and induced compressive residual stresses around the weld root by peen forming were kept even after applying the pre-loadings. Therefore, it can be concluded that peen forming, as an extended peening treatment utilization, is highly effective in enhancing the fatigue life of OSDs.

This study investigates the fatigue strength of peened-welded joints after single high compressive load peaks. To understand the relaxation behavior of compressive residual stress, out-of-plane gusset welded joints were treated using different peening methods. Compressive residual stress near the peened edge was measured using an X-ray residual stress analyzer while applying plate bending compression loads. The results showed that compressive residual stresses at 2 mm from the peened edge relaxed proportionally with increasing compression load. Strain measurements at the same location supported the estimation of stress relaxation behavior. Plate bending fatigue tests were then conducted under a stress ratio of R = 0.5. Fatigue strength decreased with increasing compression load, and under a 5.8 kN (approximately − 286 N/mm²), the fatigue strength approached that of as-weld. Finally, the fatigue results were evaluated using a newly proposed fatigue strength design curve with a cut-off limit for peening treatment, based on recommendations from the JSSC. It was concluded that this curve remains applicable if the applied compressive load after peening does not exceed 3.8 kN. Furthermore, continuous residual stress monitoring at the 2 mm confirmed that fatigue strength improvement remains effective as long as residual compressive stress is preserved during subsequent loading.