Study On Wind-Induced Response And Aerostatic Stability Of A Longspan Cable-Stayed Bridge

Long-span cable-stayed bridges are typical of being flexible and sensitive to wind,and will experience considerable vibrations due to wind loads,thus affecting the safety of the structure.Recently,the rail-cum-road cable-stayed bridge has been widely used.Research on the wind resistance performance is of great significance for ensuring the safety of the bridge and the safety of rail transit operations on it.In this paper,the proposed Fourth Bridge over the Panama Canal at the pacific side,a rail-cum-road cable-stayed bridge with the main span of 510 m,is taken as the engineering background.The study on the wind-induced responses and the aerostatic stability is carried out.The main research content is as follows:(1)The research history of geometric nonlinear theory of long-span bridges is expounded.The research status at home and abroad of the aerostatic stability as well as the wind-induced responses of the cable-stayed bridges are reviewed.Finally,the research significance,content and innovation are introduced.(2)The full spatial FEM model of the bridge is established by compiling in ANSYS software,and its accuracy is validated.Three types of geometric nonlinearities and the corresponding solving methods of nonlinear equations are introduced,and the influence of different nonlinear factors on the displacements and internal forces of the bridge are analyzed.(3)A fast spectral analysis method is used to generate the 3-D random wind speed field of the bridge based on MATLAB platform.The wind-induced responses of the long-span cable-stayed bridge is calculated in the time domain.The influence of different wind attack angles and wind speeds on the buffeting responses of the bridge is analyzed.(4)The one-incremental and two-iterative procedures are compiled based on the aerostatic stability analysis method of long-span cable-stayed bridges by APDL,and its rationality is verified.The aerostatic stability analysis of the bridge are therefore carried out,from which the influence factors such as the initial wind attack angles,wind loads on the bridge tower and cables,as well as the geometric nonlinearities on the critical static instability wind speed are analyzed.The results show that: 1)The influence of geometric nonlinearities on the bridge displacement is greater than the that on the internal forces.Considering the influence of three types of nonlinearities is the most disadvantageous.The influence is more significant by using the multi-segment chain method to consider the cable sag effect.2)The amplitude of the vertical buffeting displacement responses of the main girder is large in the early stage,and then it enters the stable state of small amplitude buffeting.The time history of the cable force is similar to that of the vertical buffeting displacement of the girder.3)The peak values of the buffeting displacement and acceleration both occur in the mid-main span due to its weak restraint.4)The critical static instability wind speed of the bridge calculated by using the two-dimensional linear torsional divergence formula recommended is higher than using the two-iterative three-dimensional nonlinear method in this paper,indicating better practical significance.