Study On Buffeting Of The ? Type Main Girder Cable-stayed Bridge In A Trumpet-shaped Mountain Pass

With the development of transportation,the construction of long span bridges in mountainous environments is becoming more and more urgent.Bridges in mountainous areas generally have the characteristics of high piers and large spans,so they are very sensitive to wind loads.Due to the complex weather and topography in mountainous areas,people's understanding of the characteristics of mountain wind field is still in a relatively backward stage.This paper chooses a?-shaped composite beam cable-stayed bridge in a typical trumpet-shaped mountain pass.The wind characteristics and wind-induced buffeting response were studied.The conclusions and scientific contributions are as follows:(1)Five wind observation masts and a Doppler acoustic radar observation station were built under a trumpet-shaped mountain pass to conduct a long-term wind observation on two long-span bridges under the mountain pass.The field measurement show that the strong wind of this trumpet-shaped mountain pass is mainly from the northwest,and the wind direction and wind speed profile are obviously twisted.For 47 consecutive years,the measured extreme wind speed of meteorological stations meets the loglogistic distribution,and the generalized extreme distribution will underestimate the return period wind speed.There is obvious spatial inhomogeneity in wind parameters.The closer to the mountain cliffs,the greater the turbulence intensity,the smaller the turbulence integral scale,the lower the power spectral density of the along-wind fluctuating wind at low frequencies,and the more obvious the nonlinear relationship between the gust factor and the turbulence intensity.The along-wind fluctuating wind power spectrum density at measuring points below 30 m will have a high-frequency sub-region phenomenon,and the introduced blunt-point power spectrum model has wide applicability.The correlation between the fluctuating wind at two measuring points separated by 765 m is described by the Davenport model,and the phenomenon of the limited fluctuation of the fitting parameter value will occur.The conditional probability density of turbulent wind parameter A_u,w satisfies the Weibull distribution,and the conditional probability density of?_u,w satisfies the Lognormal distribution.The wind tunnel test shows that the wind parameters are closely related to the local topography and the inflow direction.The spanwise variation equations of wind parameters in different inflow directions along the bridge axis are established,and the suggestions for the field measurement of the trumpet-shaped terrain are given.(2)The design parameters of the?-type composite beam section is summarized,and the typical?-type beam section is made and wind tunnel test is carried out.The experimental results show that the grid turbulence can satisfy the isotropic assumption.The angle of the wind attack will change the static pressure coefficient,fluctuating pressure coefficient and separation point.At 0°angle of attack,the correlation of the buffeting drag at low frequencies is smaller than that of the along-wind fluctuating wind,and the correlation of the buffeting lift is greater than that of the vertical fluctuating wind in all frequency ranges.Both the correlation of buffeting lift and the correlation of buffeting moment fluctuate at low frequencies.The grid type and section shape will significantly change the buffeting force spectrum and the buffeting force coherence function.The aerodynamic admittance function of the cross section at the different angles of attack is identified and the objective function is fitted.(3)Based on the measured uniform wind parameters of the trumpet-shaped terrain,the buffeting of a?-girder cable-stayed bridge is studied in the following four aspects:(1)The difference between the buffeting response under the measured wind characteristics and the normalized wind characteristics is studied,and the buffeting response results of?-type girder under different aerodynamic admittance functions are discussed.(2)The probability model of wind parameters is established,and the extreme value of the buffeting response of the main girder is estimated by the environmental contour method and the first-order reliability method.(3)Based on the measured twisted wind speed and wind direction profiles,a calculation method for buffeting response of the variable cross-section bridge tower under twisted wind profiles is established,and the influence of different wind profile types on buffeting response is compared.(4)Based on the principle of virtual work,the mode coupling buffeting control equation of the multi degree of the freedom control is derived.The traditional DTMD is improved,and the evaluation standard for the stroke of TMD is proposed.The advantages and disadvantages of multi-mode control and single-mode control are discussed,and the vibration reduction effects under different optimal parameters and frequency spacing are compared.(4)The buffeting calculation models of long-span bridges with spanwise variation of the mean wind speed and wind yaw angle,spanwise variation of the mean wind speed and wind attack angle,and spanwise variation of the mean wind speed and arbitrary wind direction are established.The effect of the spanwise variation of mean wind parameters on buffeting response is discussed.The buffeting calculation theory considering the spanwise variation of mean wind parameters,turbulent wind parameters and aerodynamic admittance function is proposed,and the effects of non-uniform wind parameters on the buffeting response are compared.