Study On Aerostatic Characteristic Of Variable Cross-section Long Span Continuous Steel Box Girder Bridge

With bridge span increasing,the structure gets more flexible and the rigidity is intensely reduced and wind loading becomes one of the important loadings for bridge.In the study of wind loading,the three aerostatic coefficient change curves is close to wind loads on structures which is basis of analyzing the wind load and important parameters in bridge wind engineering.There are two methods in current study of three aerostatic coefficient.One is based on bridge segmental model test and wind tunnel test,which results long test cycle,costly expenses and hard to observe,another is based on Computational Fluid Dynamics(CFD),which can educe the three aerostatic coefficient approximately and the flow fields distribution characteristic around sections(Visible flow field).The CFD technology is widely used in primary bridge design stage to extract bridge aerodynamic parameters,which provides basis for wind loads design.CFD technology combined with wind tunnel test is an effective method to study bridge wind engineering.This article takes a variable cross-section continuous steel box girder as its researc h background.Its main contents are as follows:(1)This paper introduces the basic theory and method about Computational Fluid Dynamics,including fluid definition,control equation,grid classification,turbulence simulation and turbulence model.This paper based project on a continuous steel box beam,analyzing self-vibration frequency and mode equation through ANSYS and MIDAS software,then compared results from the two softwares,which differ little in lower order frequencies.It means that it is possible to set up an ANSYS model that replaces complicated steel box girder by fish-bellied type.(2)This paper studies the project in linear Variable cross-section segment,which is the relationship between section changing forms and the three aerostatic coefficient through CFD technology.Choose 9 sections in the variable cross-section segment and calculate the three aerostatic coefficient on each section in-12°~12° attack angle by FLUENT,summing 117 conditions.The study shows that in the condition that sections height linear change and in 0° attack angle,there are some change laws on sections about drag coefficient and lift coefficient,but not significant change about torque coefficient.Then the study gets pressure distribution profiles,velocity profiles and stream line profiles by Numerical Simulation.It is further verified that the superiority of CFD in the aspect of computational fluid dynamics from the result.(3)This paper educes the approximate formula of equivalent wind load on project,which divided equivalent wind load into mean wind load,background wind load and inertial wind load,then educes gust response factor formulas on max single-cantilever state and max double-cantilever state simplified in order to convenient for calculating equivalent wind load in practical engineering.Calculate displacement and internal force on four key sections which based on the condition of longitudinal and transverse d irection loading in the finished bridge state.And this paper solved main girder response s in the state of double-cantilever and single-cantilever.