Experimental study of fatigue behaviour of Q690qENH bridge weathering high-strength steel welded joints

The Q690qENH weathering high-strength steel has a considerable potential for bridge engineering due to its superior mechanical strength, toughness, and corrosion resistance. To evaluate its performance under fatigue loads, the high-cycle fatigue behaviour of Q690qENH base metal and its welded joints is studied. A total of 68 specimens are tested to obtain their stress-fatigue life (S - N) curves. Results show that the fatigue strengths of the base metal, butt-welded joint, and cross-welded joint are greater than those specified in the ANSI/AISC 360-16, Eurocode 3-2005, and BS 7608-2014 design standards. The most suitable S - N curve for evaluating the fatigue properties of the Q690qENH base metal, butt-welded joint, and cross-welded joint was deemed to be that given by ANSI/AISC 360-16. New S - N curves were proposed for the base metal and butt-welded joint, whereas the S-N curve for the cross-welded joint remained unchanged as per the existing codes. Additionally, the cumulative fatigue damage behaviour of the butt-welded and cross-welded joints was analysed, and a safety threshold based on the ratcheting strain rate was established to provide early warning at 85%-95% of fatigue life. Through digital image correlation and fatigue fracture analysis, the cause of fatigue fracture in the welded joints was determined to be caused by stress concentration at the weld toe.