Study On Vortex Resonance And Its Control Of Long Span Continuous Bridge With Steel-Box Girder

Long span continuous bridge with steel-box girder will be very senstive to obvious vortex-induced resonance in less than the design wind speed, when its girder trends to be bluff shape of cross sections, flexible, light and small damping. It is observed that Trans-Tokyo Bay crossing bay bridge in Japan and Rio-Niter6i bridge in Brazil occur distinct vortex-induced vibration as typical resprentatives of continous bridge with steel-box girder. Although vortex resonance is a kind of limited amplitude response, it ocurs at low wind speed and in high probability with relative large amplitude,which will affect fatigue of the structure, bring discomfort of passengers, even endanger security of driving. Howerer, research on wind vibration of long span continuous bridge with steel-box girder in china is very poor, lacking of high attention, nearly no experience of its vibration reduction measures can be taken for reference.In this thesis, based on the longest span of continous bridge with steel-box girder in demostic, vortex resonance and relative vibration control of the kind of bridges is studied. The main work of this thesis is listed as follows:First of all, analysis theory and research method of vortex resonance is reviewed. In view of the bridge with6spans varying-depth and separated the steel-box girders, full areoelastic model testing of its scale of1:45during completion stage is studied by wind tunnel test. Then, qualitative explaination of vortex resonance is made through analysising wind speed and wind pressure layout of key bridge section by CFD software.Secondly, using finite element software to simulate the bridge-TMD (tuned mass damper) system, brief discussion on influence of bridge dynamic characters is made by respectively changing quality ratio, frequency ratio and damping ratio of TMD parameters, which provides a suitable scope for selection of TMD parameters.Thirdly, based on the semi-analytical nonlinear aerodynamic vortex force theory, bridge-TMD model in vertical direction is constructed by identifying aerodynamic parameters of bridge in the vortex "lock-in" region. Influence on maximum amplitude of the bridge is disscussed by adopting different TMD parameters, and the simplified formulas for the optimum TMD parameters are summarized. Furthermore, the optimal paramenters of TMD are concluded by programing matlab software via gradually iteration method. Credibility of vibration control model and conclussions in the thesis is checked by bridge specification and bridge-TMD model of vortex force as harmonic load.Finally, using the optimized TMD parameters, the TMD passive control plan of the bridge is designed. The amlitude, acceleration and other values of the bridge with or without TMD, are calculated, when vortex-induced vibration occurs under different wind angles of attack and different structure dampings. Comfort feeling of passengers on the bridge with TMD or without TMD is evaluated by combining wind-resistent design specification and popular rule of comfort index (Acceleration Index and Amplitude Diekmann Index). Some results prove passive control measures more effectively.