Quantification And Prediction On Flutter Performance Of Flat Box Girder

The study on influence of aerodynamic configurations and wind attack angles on flat box girder flutter performance was conducted.15 sectional models were designed adopting the width height ratios and slopes of inclined web as variables,and the flutter onset speeds of different sectional models under construction state and full bridge state with 5 different wind attack angles were tested by wind tunnel tests.The results showed that,under 0° and positive wind attack angle,for the flat box girder with the side ratio 11 and 9,the flutter onset speeds increased with the slope of inclined web decreased.However,for the flat box girder with side ratio 7,the slope of inclined web had no influence on its flutter performance.Under negative wind attack angle,the flutter onset speeds decreased with the slope of inclined web decreased.In a conclusion,the flutter performance of flat box girder achieve the optimal aerodynamic effect with a 15°web inclination.Based on bending-torsional close-form solution coupling flutter formula,the influences of aerodynamic configuration and wind attack angle on flutter performance were quantified by the flutter factors as the reduction coefficients.The coefficients are positive correlation to flutter performance of flat box girder.For the flat box girder with the side ratio 11 and 9,the reduction coefficients are not very different with each other.For the flat box girder with the side ratio 7,the reduction coefficients are greater then the coefficients of girder with the side ratio 11 and 9.According to flutter derivatives obtained from forced vibration test,conclude the rule of reduction coefficients varied with reduced wind speed,and predict the flutter performance of flat box girder.Finally,verify the accuracy of reduction coefficients by comparing the flutter critical wind speed calculated by reduction coefficients with the wind tunnel test results.Compared to the fixed reduced coefficient in the code,the reduction coefficients can specific reflect the influences of aerodynamic configuration and wind attack angle on flutter,and can be used to calculate an acceptable flutter onset speed fast and accurately.