Multi Mode Vortex Induced Vibration Of Long Span Bridge Girder Under Nonuniform Spanwise Flow

In recent years,with the increase of the span of long-span bridge,the bridge becomes softer and softer,which is prone to inspire vortex-induced vibration under low wind speed.In addition,more and more long-span bridges are built in the coastal and mountainous gorge areas.The flow field around these landforms is non-uniform,and the distribution of incoming flow along the span direction of the bridge is not uniform,which is easy to stimulate multi-mode vortex-induced vibration.Although vortex-induced vibration does not cause divergence damage like flutter,it will cause inconvenient transportation and economic loss.Therefore,it is of practical significance to study the multi-mode VIV of long span bridge girder under nonuniform flowBased on the wind tunnel test,this paper studies the multi-mode vortex-induced vibration response of long span bridge girder under non-uniform spanwise nonuniform flow.Designs and makes a 1:60 scale model of the Great Belt bridge in Denmark,designs two kinds of non-uniform incoming wind speed profiles: linear profile and parabolic profile,and compares the actual measured non-uniform wind speed profile with the designed one,the measured wind speed profile is in good agreement with the designed profile.In this paper,the response of multi-mode vortex induced vibration(VIV)under six groups of working conditions are analyzed through the taut strip model test.The vibration characteristics of the main girder under the working conditions without and with railings are discussed respectively.The influence of railings on the VIV of the main girder is analyzed and its mechanism is discussed;the variation law of wake frequency with wind speed is analyzed,and the variation law of wake frequency along the spanwise distribution of main girder with or without railings is studied.In this paper,POD mode time-frequency analysis and energy analysis are carried out for six groups of working conditions,the POD eigenvalues and modal coefficients are extracted,the variation law of modes of each order of the taut strip model with wind speed is studied,and the energy proportion,time-domain response and spectrum characteristics of each mode are analyzed.The results are similar with the direct timefrequency analysis.Pod method can not only analyze the time-frequency response of vortex-induced vibration,but also analyze the energy proportion between various modes,and even find the information ignored in direct time-frequency analysis,improve the vibration information,and be more conducive to the analysis of multimodal response.