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. © 2020, Journal of Railway Engineering Society, Editorial Department. All right reserved.