The Effect Of Railing Spanwise Arrangement On Vortex-induced Vibration Of Steel Box Girder With Vertical Webs

The characteristics of long-span bridges,such as low damping and light weight,make it increasingly important to study the evaluation indexes of wind-resistance performance,windinduced vibration theories,and mechanism of aerodynamic mitigation measures.For bridge girders,the vortex-induced vibration(VIV)occurs from time to time,which can affect the safety and the life of the structures and reduce the driving comfort.For the steel box girder with vertical webs,because of the large angles between the inclined webs and the bottom plate and the extension of the cantilever sections,as well as the influence of the auxiliary facilities on the bridge deck when it is completed,it has obvious bluff characteristics and is prone to the phenomenon of VIV.The followings are the main works of this paper:(1)The paper takes a bridge engineering project with steel box girder with vertical webs as the research object and evaluates the aerodynamic performance by wind tunnel test with normal scale model.It indicates the relationship between the wind-induced vibration responses of the main girder and the wind attack angles.Then,the uneven spanwise layouts of the outer railings have been found to reduce or eliminate the vibration efficiently.Given that the conventional scale model may have manufacture errors,so a large-scale segment model is designed to verify those results,which shows the correctness of this spanwise arrangement of aerodynamic mitigation measures.Based on the results of wind tunnel tests,this paper focuses on the study of the characteristics of flow-field of original section and the section with spanwise irrelevant aerodynamic mitigation measures.(2)Bending vibration occurs in two different scale segment model,so this type of vibration has been selected as the main content of the study.Considering the spanwise non-uniformity of aerodynamic measures,a geometric model with the same size as the large-scale model is established for three-dimensional numerical simulation research.Large Eddy Simulation technology is used to obtain the whole flow field transient information.From the perspective of velocity distribution,the development and evolution of three-dimensional vortex structure and surface pressure distribution in main girder,the cause of vibration can be analyzed.Coupled with comparative analysis,the mechanism of efficient aerodynamic mitigations can be explained from two aspects,its influence on flow field and its influence on aerodynamic force.(3)Based on above research,the flow field test research for the large-scale segmental model has been carried out.In order to obtain the flow field information in the whole space of the large model,this paper designs a new type of flow field test device for large-size structure.By capturing the information of the flow field around the model,the velocity field around the main beam is constructed,and the influence of aerodynamic measures on the velocity distribution around the flow field is analyzed.Focusing on the characteristics of the wake region of the girder,it explains the efficiency of vibration mitigation of aerodynamic measures from the perspective of frequency domain.