正交异性钢桥面板U肋-盖板焊接节点的疲劳性能试验

Fatigue Test on U-Rib-to-Deck Connections in Orthotropic Steel Bridge Decks

为深入研究正交异性钢桥面板U肋-盖板焊接节点的疲劳性能及其破坏机理,设计了6个足尺试件模型开展试验研究。首先进行中心加载和偏心加载两种加载工况下的静力试验,对焊缝附近区域的钢板表面应力进行实测,得到热点应力分布规律及应力集中系数;随后进行不同热点应力幅下的高周疲劳循环加载,得到相应的疲劳破坏模式、疲劳寿命、疲劳裂纹扩展过程及速率、刚度退化等实测数据。结果表明:U肋-盖板焊接节点的最大热点应力位于盖板焊趾处;节点在循环荷载作用下的疲劳裂纹扩展过程大致分为裂纹萌生、裂纹稳定扩展、裂纹贯穿壁厚、断裂失效4个阶段,且裂纹贯穿盖板壁厚之后的剩余疲劳寿命可忽略不计;疲劳开裂初期的裂纹扩展速率较为稳定,裂纹贯穿盖板厚度之后的扩展速率明显加快;节点刚度在裂纹长度达到150 mm时开始出现下降趋势,并在裂纹贯穿盖板厚度之后发生刚度急剧退化。通过疲劳寿命数据对比,可以认为采用IIW规范的FAT100级S-N曲线对正交异性钢桥面板U肋-盖板焊接节点的疲劳寿命进行预测和评估是偏于安全的。

In order to deeply investigate the fatigue behavior and failure mechanism of U-rib-to-deck weld connections in orthotropic steel bridge decks,6 full-scale specimen models are fabricated for the experimental study. The static tests,where load cases of centric and eccentric loadings are both conducted,and the stresses on the steel surfaces near welds are recorded to obtain the hot spot stress distributions and the stress concentration factors at first. High-cycle repeated loading are subsequently applied to the specimens with different hot spot stress ranges, and the measured data including failure pattern, fatigue life, crack propagation process,crack growth rate,as well as rigidity degradation of the specimens are obtained. The result shows that（ 1） the weld toes on deck plate provide the highest hot spot stresses of U-rib-to-deck weld connections;（ 2） the fatigue crack propagation process of the connections under repeated loading could be divided into 4 stages,i. e.,crack initiation,crack stable propagation,crack running through plate thickness,and fracture failure,and the residual fatigue lives after the crack running through plate thickness could be neglected;（ 3） the crack growth rates in the initial stage are stable,while the growth rates after runningthrough plate thickness are obviously accelerated;（ 4） degradations of connection rigidities are first observed for specimens when the single crack has been accumulated to be 150 mm long and could be significantly aggravated when the crack has run through the plate thickness. Conservatively,based on the comparison of fatigue lives,the FAT100 S-N curve as provided in the International Institute Welding（ IIW） fatigue recommendation could be used to predict the fatigue lives of such U-rib-to-deck welded connections in orthotropic steel bridge decks.