钢箱梁U肋嵌补段疲劳开裂机理与养护措施研究

某大型悬索桥为主跨1650 m的两跨连续钢箱梁悬索桥,加劲梁采用扁平流线型分离式双箱。近2年在正交异性板钢箱梁顶板U肋嵌补段发现焊缝开裂状况,为研究及处治该病害,采用大型有限元程序ANAYS进行局部仿真计算,分析焊缝开裂后的应力分布规律、影响范围。结果表明:重车轮压的疲劳荷载、施工焊接质量等是嵌补段焊缝开裂的主要原因;钢箱梁顶板U肋嵌补段焊缝开裂会对邻近结构抗力产生影响,U肋嵌补段开裂使相邻U肋嵌补段焊缝应力增加11.8%,使U肋与顶板之间焊缝主拉应力增加57%,使邻近位置的横隔板弧形缺口主拉应力增加6%。根据分析结果建议尽早处治焊缝开裂问题,短期养护措施推荐在低应力区打止裂孔和设置临时支撑架,长期养护措施建议刨去已开裂焊缝后补焊、嵌补段整体切割后补焊和改用高强度螺栓连接方式。

Study of Fatigue Cracking Mechanism for Location of Steel Box Girder Where U Ribs are Embedded and Added As Well As Maintenance Measures

A long-span suspension bridge is a continuous steel box girder suspension bridge with two spans,among those,the main span is 1650 m long.The stiffening girder consists of two separately-arranged streamlined flat steel boxes.In the recent two years,cracks have been observed in the locations of top plate of the orthotropic steel box girders where U ribs are embedded.To study and treat the deterioration,the finite element software ANSYS was used to carry out local simulation calculation,to analyze the distribution law and influential scope of stresses after the welding joints are cracked.The results demonstrate that the fatigue loads from heavy vehicles and construction welding quality are the main factors inducing cracking in the sections with U ribs.The welding joints at the locations of steel box girder top plates where U ribs are embedded will influence the cracking resistance of the adjacent structure.If the locations where U ribs are embedded are cracked,the stresses in the welding joints of the adjacent sections with U ribs would increase by 11.8%,the main tensile stresses in the welding joints of U ribs and top plates would increase by 57%,and the main tensile stresses in the arc gaps in the diaphragms would increase by 6%.According to the analysis,it is suggested that measures should be taken as early as possible to treat cracking of welding joints.Drilling anti-cracking holes in the low-stress zones and install temporary supporting frames are recommended for short-term maintenance,but for long term effect,the already-cracked welding joints should be chiselled away and at the same locations,new welding joints are made.The sections with U ribs embedded or added should be cut off as an entirety,at the same locations,new sections are welded for compensation,and the high-strength bolt connection is used.