Numerical Simulation Of Aerodynamic Characteristics Of Steel Box Girder Bridge Under IEC Gust Wind And Turbulence

Modern bridge is very sensitive to wind load due to its high flexibility,so wind load is one of the key factors in bridge design.In particular,the dynamic effect of turbulent components in the wind on the bridge is a key issue in the wind-resistant study of bridge.At the present,the static gust coefficient has been specified in the Chinese wind-resistant design specification for highway bridges and widely used to calculate the lateral static gust load of the bridge.Based on this,aerodynamic characteristics of the continuous steel box girder bridge are analyzed under the combined effect of IEC(International Electrotechnical Commission)gust wind and grid turbulence in this paper.The main contents and results of this paper are as follows:(1)The CFD(Computational Fluid Dynamics)numerical simulation of two-dimensional model of cylinder,square column and rectangular column is carried out in Fluent software,and the numerical simulation of two-dimensional bridge section is further carried out,and the calculated three-component force coefficient is compared with wind tunnel test data.The results show that the numerical simulation results in this paper are close to the experimental results,and the turbulence model selected in this paper can accurately simulate the aerodynamic force of this kind of two-dimensional calculation model.(2)Three-dimensional turbulent flow fields of two passive grids schemes are numerically simulated.In the first scheme,the monitoring surface is set at the downstream of the flow field about 6.7 times the grid spacing,and in the second scheme,the monitoring surface is set at the downstream of the flow field about 13.3 times the grid spacing.By evenly arranging monitoring points on the monitoring surface,the turbulence intensity,turbulence integral scale and fluctuating wind speed power spectrum at the monitoring surface are obtained.The analysis of the flow field characteristic parameters shows that the turbulence characteristic parameters obtained from the first scheme are close to the experimental results.This verifies the accuracy of the numerical simulation of the grid turbulence field in this paper.All grid turbulence flow fields at the location of the monitoring surface show a good uniform turbulence.(3)Using the UDF(User Defined Function)interface in Fluent software,the velocity of grid turbulence inlet boundary condition is defined as IEC gust wind.The three-dimensional bridge section model is set at the downstream monitoring surface of the flow field in the second scheme,and the time-history of the aerodynamic coefficients of the bridge section model under the combined effect of IEC gust wind and turbulence are calculated.It is concluded that the amplitude of the time-history of the aerodynamic coefficients near the peak of the IEC gust wind is large,especially for the time-history of the lift coefficient.And the calculated value of the time history curve of the aerodynamic coefficients of the bridge section lags behind the theoretical value.(4)Using the calculated time-history of the aerodynamic coefficients,the corresponding time-history loads of the bridge section under the combined effect of IEC gust wind and turbulence is obtained.Then,the time-history loads are applied to the finite element model of the continuous steel box girder bridge established by the finite element software Midas in the form of dynamic node load.The dynamic response analysis is further carried out to obtain the vertical,lateral and torsional displacement responses of each control section on the main beam.It is concluded that the vertical displacement of each section of the steel box girder is greater than the transverse displacement,and the maximum transverse,vertical and torsional displacements of each section lag behind the theoretical peak of IEC gust wind.