上坝夹江大桥钢箱梁施工方案比选及关键技术

Construction Scheme Selection and Key Technology for Steel Box Girder of Shangba Jiajiang Bridge

浦仪公路西段上坝夹江大桥采用独柱钢塔分离式钢箱梁设计,项目具有索塔刚度偏弱、超宽钢箱梁横向刚度偏弱、匹配困难的技术难点。结合桥梁边跨位于浅水区的水文条件,经过多方比选,钢箱梁最终选择“边跨高支架存梁+中跨单悬臂拼装”工艺。钢箱梁在桥位现场高支架上焊接成大节段,梁段顶底板焊接收缩不均匀将导致梁段间夹角改变,梁段自由线型发生改变。从梁段支撑反力测量、恢复的角度出发,调整梁段线型,避免箱梁顶底板不均匀收缩引起线型误差累积。钢箱梁悬拼节段的横梁位于前端,为不对称布置,吊装过程中箱梁左右幅提升的同步性至关重要。通过建模分析,有无临时横撑对梁段在吊装过程中的变形和应力影响较小,最终确定不设临时横撑方案。钢箱梁悬拼节段和起吊节段因受力不一致存在横向错缝问题在分离式结构中体现较为明显,随着箱梁悬臂长度增加,箱梁横向刚度降低,错缝有进一步增加的规律。项目实施过程中采用了设计的调整工装较好解决此类问题。结果表明:大桥成桥线型良好,结构受力合理。“边跨高支架存梁+中跨单悬臂拼装”工艺对于塔柱刚度偏弱和边跨位于浅水区斜拉桥施工均有良好借鉴意义,钢箱梁支架上大节段焊接施工的线型调整措施及悬拼梁段匹配方案可为类似项目提供参考。

The Shangba Jiajiang Bridge in the western section of Puyi Highway adopts the design of single-column steel pylon separated steel box girder,the project has the technical difficulties such as weak cable pylon stiffness,weak lateral stiffness of ultra-wide steel box girder,and difficult matching.Combining with the hydrological conditions of the bridge side span located in shallow water area,after comparison and selection,the process of“side span high bracket storage girder+mid span single cantilever assembly”is finally chosen for the steel box girder.The steel box girder is welded into large segments on the high bracket of the bridge site.If the welding shrinkage of the top and bottom plate of the girder segment is uneven,the angle between the girder segments will change,and the free geometric shape of the girder segment will change.From the perspective of girder segment support reaction measurement and recovery,the geometric shape of the girder segment is adjusted to avoid the accumulation of geometric shape errors caused by uneven shrinkage of the top and bottom plates of the box girder.The cross girder of the steel box girder cantilever segment is located at the front end,which is asymmetrically arranged,the synchronization of the left and right hoisting of the box girder is crucial.Through modeling analysis,it is found that the presence or absence of temporary cross braces has little influence on the deformation and stress of the girder segment during hoisting process,and the scheme of no temporary cross bracing is finally determined.The transverse stagger joint between the cantilever segment and the hoisting segment of the steel box girder is obvious in the separated structure because of the inconsistent stress.With the increase of the cantilever length of the box girder,the transverse stiffness of the box girder decreases,and the stagger joint has the rule further increase.The designed adjustment tooling is used to solve such problems during the implementation of the project.The result shows that(1)the geometric shape of the finished bridge is good,and the structural stress is reasonable;(2)the process of“side span high bracket storage girder+mid span single cantilever assembly”has good reference significance for the construction of the cable-stayed bridge with weak stiffness of pylon column and side span in shallow water area,and the geometric shape adjustment measures and suspension girder segment matching scheme of large-segment welding construction on steel box girder bracket can provide reference for similar projects.