钢桥面板顶板-U肋焊缝多轴疲劳效应评估

Multiaxial Fatigue Evaluation of U-rib to Deck Welded Joint in Steel Bridge Deck

了评估顶板-U肋焊缝多轴疲劳效应,定义了主要应力分量为坐标轴向幅值最大的正应力。基于弹性力学对比了单、多轴疲劳应力,提出了采用绝对值最大的主应力与主要应力分量的偏差值δ作为多轴疲劳评判依据。建立了钢桥面板节段模型和顶板-U肋细节子模型,对细节处多轴疲劳变形和应力状态进行了评估。为了定量单、多轴疲劳寿命评估的差异,定义了疲劳寿命比R,理论推导得R-δ关系,并通过试验和有限元分析加以验证。研究结果表明:单轴荷载下绝对值最大的主应力等于主要应力分量,多轴荷载下两类应力存在偏差,偏差越大,多轴疲劳效应越显著;对于顶板-U肋焊缝,多轴疲劳效应随荷载中心线偏离焊缝位置越发显著,横隔板处顶板-U肋焊缝的多轴应力状态更为明显;R与δ3成正比,该关系为在单轴疲劳评估的基础上进行多轴疲劳寿命评估提供参考。

To evaluate the multiaxial fatigue of U-rib to deck welded joint,the main stress component was defined as the normal stress with maximum amplitude along coordinate axes.The stress state under uniaxial and multiaxial fatigue was compared based on elastic mechanics,and the deviationδbetween the maximum absolute principle stress and the main stress component was proposed as the basis for evaluating the multiaxial fatigue.Then segment model of steel bridge deck and submodel of joint detail were established.The deformation and stress state of welded joint under multiaxial fatigue were evaluated.In order to quantify the difference between uniaxial and multiaxial fatigue life assessment,the fatigue life ratio R was defined,and the relationship between R andδwas deduced theoretically,which was verified by experiment and finite element analysis.The result showed that when it was under uniaxial load,the maximum absolute principal stress was equal to the main stress component.There was a deviation between the two kinds of stresses under multiaxial load and the greater the deviation,the more significant the multiaxial fatigue effect was.The effect of multiaxial fatigue became more significant when the load center deviated from the weld position,and the multiaxial stress state of welded joint located at the diaphragm was more obvious.R was proportional toδ3,which provided a reference for multiaxial fatigue life assessment based on uniaxial fatigue assessment.