Comparison between aerodynamic admittances identified via force and pressure measurement tests

Aerodynamic admittances are important parameters in buffeting analysis,and often identified via wind tunnel test of force or pressure measurement in turbulent wind field.However, both the natural vibration of the balance-model system and the frequency-response effect of the tubing system for pressure measurement can affect the identified results of aerodynamic admittance.In this study,the aerodynamic admittances of a quasi-flat section were identified via wind tunnel tests of force and pressure measurements in conj unction with a least square method based on a colligated-residue composed of buffeting-force auto-spectrum and cross-spectra be-tween buffeting force and fluctuating wind speeds (simplified as “colligated least square meth-od”).The span-wise incomplete correlation effect of buffeting forces on the sectional model was taken into account in the identification of aerodynamic admittance based on the force measure-ment test.Two cases with and without correcting the frequency-response effect of pressure tub-ing system according to the Bergh-Tij deman’s formulae were considered in the identification of aerodynamic admittance based on the pressure measurement test.On these bases,the influences of the natural vibration of the balance-model system and the frequency-response effect of the pres-sure tubing system on the identified results of the aerodynamic admittances were investigated by observing the discrepancies among the test results and the Sears Function,which is the theoreti-cal aerodynamic admittance of flat plate cross section.The results show that the resonance of bal-ance-model system can significantly amplify the identified results of aerodynamic admittances. Furthermore ,compared with the results of aerodynamic admittances identified via force measure-ment test,those identified via the pressure measurement test are much more reasonable in gener-al,and have much wider ranges of reduced frequency with practicable values,because the natural frequency of pressure tubing system is generally much higher than that of the balance-model sys-tem.Moreover,the values of the identified aerodynamic admittances would drop to some extent within a concerned range of reduced frequency for buffeting analyses of common long span bridges after considering the correction of frequency-response effect of pressure tubing system,because the resonance effect of tube cavity plays an amplifying role on the fluctuating pressure signals with frequencies lower than the resonant frequency of the tube.