Experimental study on fatigue behavior of butt-welded thin-walled steel plates strengthened using CFRP sheets

Welded steel joints in structures are susceptible to fatigue failure. In this context, advanced carbon fiber reinforced polymer (CFRP) possess a demonstrated potential for the fatigue strengthening of steel structures. However, limited information is available on CFRP strengthening of butt-welded joints, which are the most common joint types in steel structures. This paper presents a study on fatigue behavior of butt-welded thin-walled steel plates strengthened using CFRP sheets. A total of 34 specimens with both single-sided and double-sided strengthening were performed via constant amplitude tensile fatigue loading, and another four specimens were employed for hot-spot stress measurement. The effect of CFRP strengthening on fatigue behavior was investigated by varying the strengthening scheme (single-sided or double-sided) and the number of CFRP sheet layers. Test results showed that the fatigue life of butt-welded steel plates with CFRP strengthening increased by approximately one to ten times when compared to the fatigue life of butt-welded steel plates without CFRP strengthening. Triple-layered double-sided specimens seemed to exhibit the best effect on fatigue life; their fatigue strength at 2 million cycles increased by 34% compared to that of specimens without CFRP strengthening. Specific fatigue design S-N curves of butt-welded thin-walled steel plates with and without CFRP strengthening were proposed directly. The fatigue test results were used to calibrate a fatigue design approach for CFRP strengthened butt-welded steel plates. In addition, the effect of CFRP strengthening on stiffness degradation was also discussed.