Study On Flutter Stability And Vibration Response Due To Pedestrian Walking Of Long-Span Suspension Footbridge

With the rapid increase of suspension footbridge, footbridges are becoming lighter and more flexible, which results in an increasing sensitivity to wind action and pedestrian load. Because vibration and deformation even the disasters are more probability to happen, there is an increasing importance of aerodynamic study about wind-induced vibration, especially flutter stability, and human-induced vibration. The measures about vibration control must be taken when the vibrations are excessive.Based on the Zhangjiajie suspension footbridge whose section is optimized with fairings, the flutter stability and human-induced vibration stability of long-span suspension footbridge are studied in the thesis. The characteristics of the bridge are so prominent that the bridge is more flexible than Tacoma Bridge. Forced vibration wind tunnel test of section model and full aeroelastic bridge model wind tunnel test were carried out to study the flutter stability of the footbridge. The analysis of human-induced vibration stability was conducted and the way using Tuned Mass Damper(TMD) to reduce the vibration was researched. The main research contects and achievement are introduced as follows:1. The development history of the suspension bridge and the application condition of suspension footbridge in our country were introduced. The hazards of wind-induced vibration and human-induced vibration of the bridge were briefly presented. Then the ways to deal with the vibration were summed up. The main contents of this thesis were given.2. The characteristic of the Zhangjiajie suspension footbridge was analysed, and the similar requirements for making full aeroelastic bridge model were described.Based on the similar requirements, full bridge aeroelastic bridge model with variable stiffness girder and spacial cable system was designed, and the dynamic behavior test result met the requirement. The factors affecting the main girder stiffness were analyzed, and a method for pre-processing model wire of the hangers was put forward.3. In order to study the effect of the fairing, the forced vibration wind tunnel test of the section model was carried out and eight flutter derivatives were calculated, then the method for analyzing three-dimensional full-mode flutter was used to evaluate flutter stability. The analysis result and full aeroelastic bridge model wind tunnel test showed that fairings are able to improve the flutter performance of bluff girdersection significantly, and the final design of Zhangjiajie suspension footbridge can reach a higher flutter critical wind speed, which satisfied the requirement of flutter stability.4. Based on the vibration characteristics of the pedestrian bridge and the evaluation of comfort, analysis of the vibration responses to the different pedestrian loads, and the research of vibration control on the basis of the TMD system were carried out, then the parameter of the TMD using eddy current damping(ECD) was preliminary calculated. Research showed that, when the number of synchronous pedestrian on the bridge exceeded 200, the acceleration response went beyond the limit of very comfortable level, when the number was more than 400 people, the uncomfortable feeling may appear; the TMD system had a good control performance,and the effect was more obvious when the mass ratio(<2%) increased.