钢桥面板弧形切口疲劳裂纹切割修复与优化

Fatigue Crack Repair and Optimization of Cope Holes in Orthotropic Steel Decks

对正交异性钢桥面板的弧形切口进行疲劳修复时,切割孔形的优劣决定了疲劳修复效果。以检查到较多弧形切口疲劳病害的钢桥面板为研究对象,采用有限元和结构力流法分析了弧形切口处应力集中的原因。结合4种修复方案对切割孔形的圆弧半径、直线长度和倾角进行参数优化,得到了切割孔形对峰值应力的影响规律。依托钢桥面板弧形切口疲劳裂纹切割、修复工程,选择切割前、后的弧形切口开展试验研究。采用试验车进行纵向和横向移动加载,测试了2片横隔板弧形切口断面和侧面的应力分布规律和轮载位置-应力变化关系,并采用修正名义应力法近似评估其疲劳寿命。研究结果表明:轮载产生的力流通过U肋以剪应力的形式传递给横隔板,力流扩散中遇到弧形切口的阻碍,导致切口处力流高度密集;弧形切口开孔尺寸宜小,开孔半径宜大,避免阻碍力流传递路径;弧形切口优化后,其峰值应力降低58.4%,考虑横向概率分布的等效应力降低55.2%;因增大弧形切口的开孔而削弱截面面积,导致横隔板的平均压应力稍有增大;基于有限元计算和试验测试的峰值应力进行疲劳寿命预测,修复前的疲劳寿命分别为3.8年和7.2年,修复后的寿命分别为58.5年和184.4年,说明此切割修复方法具有良好的加固效果。

During the process of repairing of cope hole fatigue in orthotropic steel decks(OSD), the fatigue rehabilitation results depend largely on the quality of cutting geometries. An OSD with several cope hole fatigue cracks was investigated, and the cause of stress concentration at the cope holes was analyzed via finite element analysis(FEA) and the structural force flow method. The parameters of cope hole geometry, including the radius of arcs and length and angle of straight lines, were optimized based on four different types of repairing programs. Furthermore, the effects of cutting geometry on the maximum stress were also determined. Several cope holes were selected to conduct an experimental study, before and after the cutting repair process, which relied on the fatigue crack cutting and repair engineering in the OSD. Longitudinal and transversal movement loads were applied via an experimental vehicle, and the stress distribution and the relationship between wheel load positions and stresses were tested at the normal section of the cope holes and on both sides of the diaphragms. Finally, the modified nominal stress method was employed to estimate the fatigue life of the cope holes. The study indicates that the stress flow, generated by wheel loads, passes through the U ribs and then spreads to the diaphragms in the form of shear stress. However, the stress flow is obstructed by the cope hole, which results in stress concentration surrounding the cope hole. The size of the cope hole should be small, while the radius of the cope hole should be larger, and the path of stress flow should be unobstructed. After the cope hole was optimized, the stress reduction proportion attained a value of 58.4%, and the equivalent stress amplitude, which considered the lateral probability distribution, reduced to 55.2%. Enlarging the size of the cope holes leads to the reduction in the section area and thereby results in a slight increase in the average compressive stress in the diaphragms. Based on FEA and experimental stress, the fatigue life of the cope hole before repair are respectively 3.8 years and 7.2 years, and the fatigue life increases respectively to 58.5 years and 184.4 years after repair, which indicates that the cutting repair method exerts a positive effect.