Time-domain Simulation And Analysis On Nonstationary Buffeting Responses Of A Long-span Suspension Bridge Under Typhoon Actions

Long-span suspension bridges are developing along a trend of softening,thus the sensitivity to wind loads is becoming increasingly significant.In recent years,typhoons and other extreme wind disasters have occurred frequently and exhibit an obvious nonstationary feature.The wind-induced dynamic responses of long-span suspension bridges are more complicated under typhoon.However,the traditional bridge buffeting analysis method is based on the assumption of stationary stochastic process,which is difficult to accurately predict the wind-induced responses of the bridge.Therefore,combined with the time-varying characteristics of typhoon at the bridge site,it is necessary to advance the traditional buffeting analysis framework on the basis of stationarity,and further study the nonstationary buffeting responses of long-span suspension bridges under typhoon actions.The purpose is to improve the safety and applicability of long-span bridges under extreme wind conditions.Surrounding the nonstationarity of both typhoon environment and buffeting responses,the time-domain simulation and analysis of nonstationary buffeting responses of a long-span suspension bridge under typhoon actions are conducted.The main contents of this thesis mainly include:(1)Finite element modeling and modal analysis of the long-span suspension bridge.According to the structural design parameters of the Runyang Suspension Bridge,one three-dimensional finite element model is established.Modal analysis of the bridge is then conducted by subspace method and the first 30 natural frequencies and vibration modes are obtained.Simultaneously,comparisons are also carried out among the calculated typical modal parameters,the measured modal parameters of the scale model and the third-party calculated modal parameters.(2)Analysis of nonstationary characteristics of the measured typhoon.According to the measured wind records,the nonstationary characteristics of the typhoon is analyzed.The time-varying average wind speed is extracted by wavelet transform.Then based on the nonstationary/stationary wind models,the turbulence intensity,gust factor and turbulence integral scale of the fluctuating wind in the two models are calculated and compared.On this basis,the power spectrum of stationary wind and the evolution power spectrum of nonstationary wind are studied.Based on the principle of nonlinear least squares,the power spectrum and evolution spectrum model of the measured wind velocity are fitted both in the along-wind direction and vertical direction.(3)Three-dimensional nonstationary fluctuating wind field simulation of the longspan suspension bridge.Based on the fitted evolution power spectrum models in the along-wind direction and vertical direction,the nonstationary fluctuating wind field of the long-span suspension bridge are generated by the harmonic synthesis method of nonstationary wind field after the time-domain spectrumd ecoupling is realized with the POD method.Meanwhile,the simulated wind field is tested from two aspects of evolution power spectrum and correlation functions.(4)Time-domain simulation and analysis of nonstationary buffeting responses of the long-span suspension bridge.Based on the nonstationary buffeting theory,numerical simulation analysis of the nonstationary buffeting responses of the Runyang Suspension Bridge is investigated in time domain with both of the aerodynamic selfexcitation and structural nonlinearity taken into consideration.The analytical results are performed with a comparison to the stationary time-domain results,which verifies the necessity of considering the nonstationary wind load when analyzing the buffeting response of long-span suspension bridges under typhoon actions.