Proactive strengthening of U-rib butt-welded joints in steel bridge decks using adhesively bonded Fe-SMA strips

Abstract

U-rib butt-welded joints are one of typical fatigue-prone details in early aging orthotropic steel bridge decks, which poses a potential threat to the structural behavior and safe operation of steel bridges. Therefore, it is of great importance to seek out an effective way for retrofitting fatigue cracks. This study proposes an efficient prestressing technique using bonded iron-based shape memory alloy (Fe-SMA) to strengthen cracked U-rib butt-welded joints proactively. A series of static and fatigue tests were conducted on the cracked specimens to investigate the feasibility and fatigue improvement of the proposed technique. Results from the experiments demonstrated that applying prestressing force by heating Fe-SMA strips is a convenient and reliable technique. Activated Fe-SMA strips could introduce significant compressive stresses and provide additional stiffness for the cracked components. This led to a reduction of the mean stress and fatigue stress ranges at the U-rib butt-welded joints under cyclic loading. All the cracked specimens strengthened with adhesively bonded Fe-SMA strips presented excellent fatigue performances, with a maximum equivalent fatigue life extension of 4.09 times compared to the specimen before cracking. Numerical simulation was also performed to better understand the test results. It was demonstrated that prestressed Fe-SMA strengthening could decrease the mode-I stress intensity factor (SIF) at the crack tip, indicating the beneficial effects of the prestressing in retarding crack and its further propagation. In conclusion, the use of adhesively bonded Fe-SMA strips for strengthening cracked butt welds is highly effective in improving the fatigue performance, even better than bonding CFRP.