Research on the Fatigue Performance of Rib-to-Deck Welded Joints of Wujiagang Yangtze River Bridge

The fatigue cracks in the rib-to-deck welded joints are typical fatigue diseases in orthotropic steel deck. The fatigue crack penetrating through the deck will cause secondary diseases such as pavement damage, water seepage and corrosion, which will endanger the durability and safety of steel box girder seriously. The natural "crack-like" structure is formed at the deck root of the traditional rib-to-deck single-side welded joints because the traditional welding technology can only weld at the outside of the U-rib, which causes the critical fatigue cracking problems at the deck root. In order to solve the fatigue problem of crack initiating from the deck root for traditional rib-to-deck single-side welded joints in the Wujiagang Yangtze River Bridge project, the innovative rib-to-deck both-side welded joints were proposed to improve its fatigue resistance. The rib-to-deck welded joints were analyzed systematically by the equivalent structural stress method. The influence surface of each fatigue cracking mode of the rib-to-deck single-side and both-side welded joints was determined respectively. The predominant fatigue cracking mode of the two welded joints was determined considering the lateral distribution probability of the wheel load, and then their fatigue life was evaluated.
The results indicated that the length of the longitudinal influence line of each fatigue cracking mode of the rib-to-deck single-side and both-side welded joints were mainly between the two diaphragms adjacent to the specific construction details. The fatigue cracking mode of deck root and deck toe of the traditional rib-to-deck single-side welded joints were mainly in tensile and compressive cyclic stress under the longitudinal movement of wheel load. The location(e=-150 mm) where the wheel load acts directly above the traditional rib-to-deck single-side welded joints was the most unfavorable transverse loading position. The crack initiating from the deck root was the predominant fatigue cracking mode of the traditional rib-to-deck single-side welded joints. The maximum equivalent structure stress amplitude is 70.4 MPa under the action of standard fatigue vehicle. The fatigue cracking mode of deck inner and outer toe of the innovative rib-to-deck both-side welded joints were mainly in tensile and compressive cyclic stress under the longitudinal movement of wheel load. The most unfavorable transverse loading position of the rib-to-deck both-side welded joints was same to the traditional rib-to-deck single-side welded joints. The crack initiating from the deck outer toe was the predominant fatigue cracking mode of the innovative rib-to-deck both-side welded joints. The maximum equivalent structure stress amplitude is 63.2 MPa. The predominant fatigue cracking mode of rib-to-deck welded joints was changed from the crack initiating from the deck root of the traditional rib-to-deck single-side welded joints to the crack initiating from the deck outer toe of the innovative rib-to-deck both-side welded joints by introducing the innovative rib-to-deck both-side welded joints. The fatigue life of the innovative rib-to-deck both-side welded joints was increased by about 42.4%. The introduction of the innovative rib-to-deck both-side welded joints can effectively improve the fatigue performance of rib-to-deck welded joints.