Fatigue strength improvement of out-of-plane welded joints of steel girder under variable amplitude loading

This study investigates improvement effects of fatigue strength by the postweld treatments, which are hammer peening treatment and additional welding with low-temperature transformation welding material. High cycle fatigue tests with constant and variable amplitude loadings are performed on out-of-plane gusset-welded joints of girder specimens. Test results indicate that this treatment can improve fatigue life under both the constant and variable amplitude loadings. The damage accumulations (D) of as-welded and cleaning obtained by Miner’s rule with the mean curve of constant amplitude loading are conservative (D > 1.0). However, since the beneficial effects of the compressive residual stress on fatigue life should decrease due to the relaxation of compressive residual stress, the D in specimens prepared by cleaning plus pneumatic peening, cleaning plus electric peening, and additional welding with low-temperature transformation welding material are extremely nonconservative (D ≈ 0.2–0.6). The modified Miner’s rule based on the results of fatigue test with constant maximum stress, which is the same as the maximum stress in the variable amplitude loading, is appropriate to the improved welded joints.