Experimental and comparative investigation on fatigue performance of three typical welded joints of Q370qNH bridge weathering steel

The weathering index of welded details, including butt-welded, non-load-carrying T-shaped and cruciform welded joints, fabricated with Q370qNH weathering steel was evaluated, and fatigue tests were conducted on the three types of welded details with a stress ratio of -1 to determine the fatigue modes and fatigue properties. The fatigue S-N curves of three typical welded joints are fitted using the fatigue data and compared with the existing fatigue specifications, such as Eurocode 3, IIW 2007 and China code Standard for Design of Steel Structures GB50017-2017. Total of 215 fatigue data are collected form the existing literature, the difference of fatigue performance between the WS welded joints and that of traditional structural steels was analyzed. Results show that the slope parameter m of S-N curve of Q370qNH butt-welded joint is 5.83, which is quite different from the recommended value of 3. The fitting S-N curves of T-shaped welded joints and cruciform welded joints are in relatively well correlation to the S-N design curves. The fatigue performance of non-load-carrying T-shaped welded joints is significantly better than that of butt-welded joints and load-bearing cruciform welded joints. FRI analysis based on the collected fatigue data of 13 types of metallic materials in this study indicates that the actual fatigue strength of Q370qNH welding details demonstrates a certain fatigue safety margin, especially for the non-load-carrying T-shaped welded joints.