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Research on the Fatigue Performance of Rib-to-Deck Welded Joints of Wujiagang Yangtze River Bridge
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摘要: 纵肋与顶板构造细节疲劳开裂是正交异性钢桥面板结构的典型疲劳病害，疲劳裂纹一旦裂穿顶板将引发铺装层破损和渗水锈蚀等次生病害，严重危害钢箱梁的耐久性和安全性。由于传统的焊接技术只能在闭口纵肋外侧单面施焊，使得纵肋与顶板传统单面焊构造细节焊根位置存在天然的“类裂纹”构造，导致其焊根位置疲劳开裂问题突出。为解决纵肋与顶板传统单面焊构造细节焊根位置疲劳开裂难题，依托伍家岗长江大桥项目，通过引入纵肋内焊技术，发展纵肋与顶板新型双面焊构造细节，以提升其疲劳性能。以纵肋与顶板构造细节为研究对象，基于等效结构应力法对其疲劳性能进行了系统研究，首先确定了纵肋与顶板传统单面焊构造细节和新型双面焊构造细节各疲劳开裂模式的影响面，在考虑了轮载横向分布概率的基础上确定了两种构造细节的主导疲劳开裂模式，并对其疲劳寿命进行了评估。
研究结果表明：纵肋与顶板传统单面焊构造细节和纵肋与顶板新型双面焊构造细节中各疲劳开裂模式的纵向影响线长度主要在构造细节相邻的两个横隔板之间；在轮载的纵向移动作用下，纵肋与顶板传统单面焊构造细节顶板焊根开裂模式和顶板焊趾开裂模式均以承受拉-压循环应力为主，轮载作用于传统单面焊构造细节的正上方（e=-150 mm）为其最不利横向加载位置；纵肋与顶板传统单面焊构造细节的主导疲劳开裂模式为顶板焊根开裂，在标准疲劳车作用下其最大等效结构应力幅值为70.4 MPa；在轮载的纵向移动作用下，纵肋与顶板新型双面焊构造细节的顶板内侧焊趾开裂模式和顶板外侧焊趾开裂模式均以承受拉-压循环应力为主，其最不利横向加载位置和纵肋与顶板传统单面焊构造细节相同，为轮载作用于构造细节的正上方（e=-150 mm）；纵肋与顶板新型双面焊构造细节的主导疲劳开裂模式为顶板外侧焊趾开裂，其最大等效结构应力幅值为63.2 MPa；新型双面焊的引入使纵肋与顶板构造细节的主导疲劳开裂模式由传统单面焊构造细节的顶板焊根开裂迁移到新型双面焊构造细节的顶板外侧焊趾开裂，相较于传统单面焊构造细节，新型双面焊构造细节的疲劳寿命提升约42.4%。新型双面焊的引入可有效提升纵肋与顶板细节的疲劳性能。Abstract: 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. -
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