青山长江大桥主航道桥结构动力特性分析

研究目的:青山长江大桥主航道桥是目前世界最大跨径全漂浮体系斜拉桥,桥塔为目前世界最高的A形桥塔,主梁为目前长江上最宽的钢箱梁,其动力特性是结构受力特性的关键,与常规斜拉桥相比具有独特之处。本文采用ANSYS建立空间有限元计算模型,对青山长江大桥主航道桥成桥状态、施工阶段最大单悬臂状态结构动力特性进行分析,从而为进一步进行结构抗震、抗风性能分析研究奠定基础。研究结论:(1)在成桥状态时,结构前3阶振型分别为纵飘、对称侧弯、对称竖弯,对应周期分别为14.22 s、6.25 s、4.78 s;在最大单悬臂状态时,结构前3阶振型分别为侧弯、竖弯、竖弯,对应周期分别为8.4 s、4.44 s、2.93 s,两种状态均属于长周期结构;(2)成桥状态和最大单悬臂状态时,结构侧向刚度均偏弱,对横向风致振动响应敏感;(3)结构采用A形桥塔、超宽主梁、空间双索面提高了结构的扭转频率和抗扭刚度,增强了结构的抗扭稳定性,边跨设置辅助墩提高了结构频率和刚度;(4)在成桥状态时,结构的高阶振型中出现了振型的耦合现象;在最大单悬臂状态时,结构的低阶振型中即出现了振型的耦合现象;(5)本研究成果可为大跨度全漂浮体系斜拉桥结构抗震、抗风设计提供依据。

Analysis of Dynamic Characteristics of Main Channel Bridge of Qingshan Yangtze River Bridge

Research purposes:The main channel bridge of Qingshan Yangtze River Bridge is the largest span cable-stayed bridge with full floating system in the world.Its pylon is the highest A-shaped pylon in the world and its main girder is the widest steel box girder on the Yangtze River.Its dynamic characteristics are the key to structural stress characteristics,which are unique compared with conventional cable-stayed bridges.By adapting ANSYS,spatial finite element model of main channel bridge of Qingshan Yangtze River Bridge was established,and structural dynamic characteristics at completion state and largest single cantilever state in construction stage were analyzed,which lays a foundation for further research on seismic and wind resistance performance of structures.Research conclusions:(1)At completion state,the top three order vibration modes of the structure are longitudinal wave,symmetric lateral bending and symmetric vertical bending respectively,and the corresponding period is 14.22 s,6.25 s and 4.78 s respectively.At largest single cantilever state,the top three order vibration modes are lateral bending,vertical bending and vertical bending respectively,and the corresponding period is 8.4 s,4.44 s and 2.93 s respectively.The structure in two states above belongs to long-period structure.(2)Under both states,lateral stiffness of structure is weak,and it is sensitive to wind-induced vibration response in transverse flow.(3)By adopting A-shaped pylon,ultra-wide main girder and double-cable plane,structural torsion frequency and anti-torsion stiffness are improved,and anti-torsion stability of structure is enhanced,and the structural frequency and stiffness are increased by setting auxiliary piers on the side span.(4)At completion state,coupling phenomenon of different vibration mode appears in higher-order vibration modes of structure,and corresponding to largest single cantilever state,coupling phenomenon of different vibration mode appears in lower-order vibration modes of structure.(5)The research result can provide a basis for seismic and wind resistance design of long span cable-stayed bridge with full floating system.