Experimental study on fatigue behavior of trapezoidal rib-to-deck welded joints in orthotropic steel decks strengthened with CFRP sheets

Due to the unavoidable stress concentrations and welding defects, the trapezoidal rib-to-deck welded joints of Orthotropic Steel Bridge Decks (OSBD) are prone to fatigue cracking. It is a new exploration to apply Carbon Fiber Reinforced Polymer (CFRP) sheets to strengthen the complex welded joints to improve the fatigue strength. In this paper, the comparative tests of un-strengthened and CFRP strengthened welded joints were carried out. The hot spot stress distribution under static load and fatigue behavior under cyclic load were studied, considering the influence of the number of CFRP sheet layers. The experimental results indicate that CFRP reinforcement can effectively reduce the stress concentrations at weld toe of the deck, and three-layers reinforcement has a greater effect than one-layer reinforcement. There was no significant difference in failure modes between the un-strengthened and CFRP strengthened welded joints. The fatigue cracks of all joints originated from weld toe of the deck, and then expanded along the width and thickness of the deck which caused the deck to break. CFRP reinforcement can significantly improve the fatigue life of trapezoidal rib-to-deck welded joints under the same nominal stress range and three-layers reinforcement presented a longer fatigue life. The S-N curve log N = 12.059 - 3 . log delta sigma(hs) based on the hot spot stress range at weld toe of the deck was established, which can be applied to the fatigue strength design of un-strengthened and CFRP strengthened rib-to-deck welded joints. The mechanism that CFRP reinforcement can significantly improve the fatigue performance of welded joints can be concluded to less stress concentrations and slower growth rate of the crack.