Study On The Characteristics Of Buffeting For Truss Girder Bridge In Mountain Gorge

Truss girder has the geometric features of hollowness,span-wise discontinuity,and high width-height ratio,which enhance the difficulty in spatial distribution research of aerodynamic force on truss girder.Besides,the turbulence spectrum released in the existing "Code for Wind-resistant Design of Highway Bridges" is proved insufficient to describe the fluctuating characteristics of the western mountainous gorges.Therefore,this dissertation firstly measured the gorge wind on long-span truss girder bridge site in the western mountainous areas,and carried out statistical research subsequently.Then,a determination approach for the characteristics of buffeting force on truss girder is theoretically derived,and verified through dynamic force-measurement on rigid truss girder model in grid-generated turbulence.The influence of incoming flow and geometric characteristics of truss girder on span-wise coherence of buffeting force as well as the two-dimensional wavenumber aerodynamic admittance is studied by wind tunnel tests whereafter.Empirical models for aerodynamic admittance and span-wise coherence are fitted based on the test results.Finally,the empirical models are proved liable by comparing the displacement calculation results with full bridge aeroelastic model test results.Combining the gorge turbulent spectrum with the empirical models,the effects of turbulent spectrum,span-wise coherence function and aerodynamic admittance on buffeting displacement response of truss girder bridge are analyzed.The specific research contents and main conclusions of this dissertation are as follows:1.The turbulence and average wind were observed on the bridge sites of three long-span truss girder bridges in the western mountainous gorges.Statistical study on the turbulent characteristics and average wind characteristics is carried out.Turbulent intensity of gorges in western mountainous area is much higher than normative range.Integral length scales are significantly different with the code.The peak frequency and spectral value of turbulent spectrum are higher than spectrums in the code.The average wind directions basically parallel gorge directions,and the dominant wind directions are affected by small terrains.The mean wind angle of attack has a wide distribution(-10°?+20°).Wind profile also varied from the code.2.The theory of isotropic uniform turbulence is introduced,different forms of aerodynamic admittance is clearly distinguished,and the classical empirical models of span-wise buffeting force coherence as well as aerodynamic admittance is summarized.The classical coherent models are compared for choosing the most applicable ones on truss girder.By regarding truss girder equivalent to a continuous cross-section,a three-dimensional two-wavenumber aerodynamic admittance determination approach is proposed.The formulas for coherence and correlation of buffeting force on equivalent truss girder cross-section are derived.The effectiveness of the proposed approach is verified by dynamic force-measurement on rigid truss girder model in grid-generated turbulent wind tunnel tests.Three-dimensional two-wavenumber aerodynamic admittance and two-dimensional one-wavenumber aerodynamic admittance of the equivalent truss girder cross-section are obtained.The approach is also applicable to any bluff body bridge.3.Based on wind tunnel tests,the influence of turbulence and geometric characteristics of truss girder on buffeting force are studied by changing turbulent intensity,angle of attack,width-height ratio,real area ratio and railing porosity.The main influence laws are summarized.According to wind tunnel test results,a two-dimensional aerodynamic admittance empirical model and a buffeting force span-wise coherence empirical function of equivalent truss girder cross-section are fitted.4.By adopting the Davenport function,the Karman function and the fitted empirical span-wise coherence function as coherence function respectively,using Sears function,1 and the fitted empirical two-dimensional function for truss girder as aerodynamic admittance,and taking Simiu spectrum,Kaimal spectrum,Panofsky spectrum,the turbulent spectrum measured on bridge sites,and the uniform turbulent spectrum for the western mountainous gorges fitted in this dissertation,based on the SRSS method,frequency-domain calculations on three long-span truss girder bridges of buffeting displacement response are carried out.The influence of each part is studied.The impacts of buffeting force influence factors are also discussed.