钢桥面板纵肋与顶板焊接细节疲劳裂纹扩展三维模拟方法

为了深刻认识正交异性钢桥面板的疲劳特性，准确评估其疲劳抗力，对纵肋与顶板焊接细节进行了三维疲劳裂纹扩展模拟。提出了一种主要针对椭圆或半椭圆形疲劳裂纹的扩展模拟方法，采用相互作用积分法计算裂纹尖端处的应力强度因子K，作为三维裂纹模拟的基本参量。以青山长江公路大桥正交异性钢桥面板疲劳试验节段模型为研究对象，将纵肋与顶板焊接细节处的疲劳裂纹近似为单个半椭圆形裂纹，对其扩展过程进行三维模拟，通过试验结果验证了所提方法的有效性。在此基础上将初始裂纹分别设置于焊根和顶板焊趾，探讨了顶板厚度和U肋形式对于纵肋与顶板焊接细节疲劳裂纹扩展特性的影响问题。研究结果表明：所提出的方法能够准确模拟纵肋与顶板焊接细节疲劳裂纹的扩展过程，适用于其疲劳问题研究；增加顶板厚度能够有效改善纵肋与顶板焊接细节处的疲劳性能；相对于传统纵肋与顶板焊接细节而言，顶板与镦边U肋焊根和焊趾处的疲劳裂纹扩展特性和疲劳抗力没有显著差别，顶板与镦边U肋焊缝构造细节难以显著改善焊根和顶板焊趾处的疲劳性能；萌生于焊根并向顶板扩展的疲劳失效模式是控制传统纵肋与顶板焊接细节和顶板与镦边U肋焊缝构造细节疲劳性能的主导疲劳失效模式。

3-D Simulation Method for Fatigue Crack Propagation in Rib-to-deck Welded Joints of Orthotropic Steel Bridge Deck

In order to deeply understand the fatigue characteristics of orthotropic steel bridge deck and accurately evaluate its fatigue resistance, 3-D simulation of fatigue crack propagation in rib-to-deck welded joints was carried out. A method for simulating elliptical and semi elliptical fatigue crack propagation was proposed. The interaction integral method was used to calculate the stress intensity factor K (the basic parameter of 3-D crack simulation) of the endpoints of the crack. The Orthotropic steel bridge deck model of Qingshan Yangtze River Highway Bridge was taken as the research object. The fatigue crack in rib-to-deck welded joint was simplified into a single semi elliptical crack to make 3-D propagation simulation. The validity of the proposed method was verified by model tests. The impacts of the thickness of the deck plate and the form of the U-rib on the fatigue crack propagation properties of the rib-to-deck welded joints were investigated by setting the initial crack at weld root and weld toe of the deck plate respectively. The results show that the proposed method can accurately simulate the fatigue crack propagation in the rib-to-deck welded joints, applicable to the research on fatigue problem. The increase of the deck thickness can effectively improve the fatigue performance of the rib-to-deck welded joints. In terms of rib-to-deck welded joints, there is no significant difference in fatigue crack propagation properties and fatigue resistance of weld root and weld toe of the U-rib. Fatigue properties of the weld root and weld toe are difficult to be improved by the welded joints of deck plate and U-rid. The fatigue failure mode produced at the weld root and extending to the deck plate is the leading fatigue failure mode governing the fatigue properties of the rib-to-deck and deck-to U rib welded joints.