Simulation And Measurement Analysis On Nonstationary Effects Of Buffeting Responses Of A Long-span Cable-stayed Bridge Under Typhoon Actions

The refinement on the analytical theory quantifying wind-induced vibrations of the long-span bridges is the basic and long-term research interests in the field of structural wind engineering.Under the background of obvious nonstationary characteristics captured in typhoon winds,simulation and field measurements,which surrounds the hot topic "refinements on the wind-induced vibration of bridges",on the nonstationary effects of typhoon-induced buffeting responses of a long-span cablestayed bridge are conducted.The main contents of this dissertation mainly include:(1)Analysis of nonstationary characteristics of strong typhoons and the extraction of characteristic parameters.Based on the measured data of Typhoon Fung Wong at Sutong Bridge site,the nonstationary wind characteristics of a strong typhoon wind is analyzed.Since the extraction of the time-varying trend in nonstationary winds always depends on experience,a self-adaptive method in determination of the time-varying mean wind velocity is proposed.Based on this approach,the turbulence intensity,gust factor,peak factor,turbulence integral scale and turbulence power spectral density are emphatically analyzed.The stationary and nonstationary models of wind characteristics are compared accordingly.(2)Modelling of the evolutionary power spectral density of nonstationary typhoon winds.The evolutionary power spectral densities of nonstationary typhoon winds are investigated based on the measured wind samples of typhoons.Assuming the wind in a short period is stationary,the general expression of the empirical evolutionary power spectral density is derived for typhoon winds and the validity of this model is verified.Since high-frequency subranges beyond the initial subrange is always captured in the stationary spectra of typhoons,the evolutionary power spectral model considering highfrequency subranges is further investigated and an approach determining this model is established.(3)Fast simulation of the multivariate stationary random fluctuating wind field.According to the deficiency that the simulation efficiency of the traditional interpolation-enhanced scheme is restricted to Cholesky decompositions,a new method based on the two-dimensional reduced Hermite interpolation is proposed for the simulation of stationary turbulence field.The reduced Hermite interpolation and the two-dimensional technique make the number of Cholesky decompositions independent from the number of simulation points the duration of samples to be generated,thus overcoming the aforementioned restriction.(4)Fast simulation of the multivariate nonstationary random fluctuating wind field.Under the framework of the spectral representation method,an approach based on the two-dimensional interpolation is proposed for the simulation of nonstationary turbulence field.The two-dimensional reduced Hermite interpolation renders the number of Cholesky decompositions to the cross evolutionary power spectral density matrices independent from frequency segments and simultaneously realizes the decoupling of the time-frequency spectrum.In allusion to the two cases characterized by time-varying and time-invariant coherence functions,the simulation efficiency and modelling error of the proposed approach are investigated with a comparison to the POD based approach.(5)Measurement and analysis of the nonstationary buffeting responses of a longspan cable-stayed bridge.Based on the measured vibrations of Sutong Bridge during typhoon periods,the measured buffeting responses are analyzed in a nonstationary perspective.Assuming the response in a short period is stationary,the modal frequencies and damping ratios of the bridge during typhoon periods are identified using the random decrement technique.Then,the evolutionary features and amplitudedependent properties of modal parameters are analyzed accordingly.On this basis,the time-frequency analysis on the nonstationary buffeting responses of the bridge is conducted with the wavelet transform,and then the necessity of considering nonstationary characteristics of typhoon winds in the structural buffeting analysis is further discussed.(6)Simulation and analysis of nonstationary buffeting responses of a long-span cable-stayed under the action of typhoon winds.Based on the first kilometer-level cable-stayed bridge in China,the simulation and analysis of nonstationary buffeting responses of a long-span cable-stayed bridge under typhoon winds are conducted.The nonstationary self-excited forces are expressed in time domain through the indicial function and the impulse function.Then,the time-domain buffeting analysis of the section model is performed with a comparison to the stationary time-domain results.Meanwhile,the performances of the time-domain method and the time-frequency method in the nonstationary buffeting analysis are compared.Accordingly,the framework for the prediction of nonstationary buffeting responses of bridges is summarized.Based on this framework,the multi-mode coupled nonstationary buffeting responses of a long-span cable-stayed bridge is further investigated.