Study On The Influence Of Aerodynamic Admittance Function On Buffeting Responses Of Bridge In Time-domain

Compared with frequency-domain analysis,buffeting analysis in time-domain has advantages of being able to taking into account of various non-linear factors and to obtain buffeting time-histories.The equivalent wind-spectrum and buffeting forcespectrum methods,which have been used extensively to date in buffeting time-domain analysis,have many a few shortcomings.In this paper,the buffeting loads and aerodynamic admittance are simulated in time-domain by Küssner type function,and the buffeting load expressions in time-domain based on Küssner function are derived.This paper investigates influences of different aerodynamic admittance functions on buffeting responses in time-domain,and influences of aerodynamic admittances on buffeting responses of bridge with different spans as well.The main research contents and conclusions are presented as follows:1.Time domain buffeting load expressions are obtained based on the process of aerodynamic load evolution.According to the frequency-domain equivalence of the Küssner model to the quasi-steady model modified by aerodynamic admittances,the relations between the Küssner functions and aerodynamic admittances are established.In so doing,aerodynamic admittances are is flexibly converted into time-domain,and new buffeting load expressions in time-domain are derived.2.Aerodynamic admittances of the deck section of a suspension bridge with a main span of 920 m are identified via wind tunnel tests.The test results show that there is significant difference between the identified function and the Sears function.the value of the identified admittance decreases with the frequency more slowly than does the Sears function,and the aerodynamic torque related admittance is lower than the Sears function at low frequency range.3.The Küssner function based buffeting load expressions are employed in this study to simulate the buffeting responses of a suspension bridge with a main span of 920 m.The buffeting responses have been obtained with unit aerodynamic admittance,Sears function,and tested aerodynamic admittance functions,respectively.Hence discrepancies in buffeting responses due to different aerodynamic admittance functions are investigated.The results show a significant difference between those obtained respectively from the Sears function and the tested aerodynamic admittances.Therefore,even for flat box girder section,it is inappropriate to use the Sears function for buffeting analysis.4.Seven suspension bridge models,respectively with a main span of 400 m,600m,800 m,1000m,1200 m,1400m and 1600 m,are designed to perform buffeting analysis.Unit aerodynamic admittance,Sears function,and tested aerodynamic admittance functions are employed for comparison,and the influence of the same admittance function(Sears)on buffeting responses of suspension bridge with different spans is studied.The results show that the influence of aerodynamic admittance function on the buffeting responses decreases as the bridge span increases.