Performance-based Flutter Rresponse Of Long-span Bridges Probabilistic Eevaluation Method

Flutter or buffeting response of long-span bridges is a hot research topic for wind-induced vibration response of long-span bridges.Due to the large differences in wind field types and randomness of wind fields,traditional analysis and evaluation methods lack randomness considerations,so the method of Performance-based probabilistic has gradually become a hot spot in the evaluation of wind-induced vibration response of bridges.In this paper,based on the performance-based seismic design research method,the performance-based flutter response analysis and evaluation method for long-span bridges is studied.The thesis completed the numerical simulation of the non-stationary pulsating wind field and verified the simulation results based on the evolutionary spectrum theory;on the basis of the wind field simulation,a comparative study of the chatter response under the action of normal wind and non-stationary wind field was carried out,Get the similarities and differences of the effects of different wind fields on the chatter response of the structure;Based on pedestrian and driving comfort,a probabilistic evaluation framework for the tremor response of this performance requirement was constructed,and the flutter or buffeting response under normal wind load was evaluated,obtain the damage curves under different comfort levels and the probabilistic evaluation process of flutter response under non-stationary wind field.The main research work and conclusions of the paper include: 1.Based on the process of simulating the wind with harmonic synthesis,and taking into account the time-varying mean,complete the simulation of the non-stationary wind field,and the simulation results are verified according to the evolutionary spectrum theory.Comparing the short-time average method,wavelet analysis method and EMD empirical mode decomposition to extract the time-varying mean,the method of EMD empirical mode decomposition is used to decompose due to the speed quickly,the operation simply,and higher calculation accuracy than others.In the simulation of short-time average method,the power spectrum of the simulation result is verified by the evolution spectrum,which further proves that the non-stationary wind field is formed by the superposition of a time-varying average wind and pulsating components that change with time.2.On the basis of wind field simulation,through finite element modeling and analysis,obtain the flutter or buffeting response of the structure under different wind fields,and the displacement and RMS value of the structure are compared and analyzed.Comparing the flutter or buffeting response of the time course of normal wind and non-stationary wind speed,it is found that when the non-stationary wind field acts,the lateral displacement of the bridge structure is more sensitive than the vertical and torsional displacements.The same calculation of the average wind effect results,in the nonstationary wind field,the lateral response is 2.4 times than the lateral response under normal wind.3.Based on pedestrian and driving comfort,establish a probabilistic evaluation framework under this performance requirement;by simulating the flutter or buffeting response of multiple sets of wind speed time history,the distribution laws of structural responses under the same wind speed and different wind speeds were obtained respectively;According to the evaluation framework and response distribution,calculate the demand-based damage curve.Under the effect of normal wind,the mean value of the most unfavorable response in the mid-span increases exponentially with the wind speed in the horizontal and vertical directions.And regardless of the wind speed,based on pedestrian and driving comfort evaluation criteria,the vertical damage of the structure is more sensitive than the wind speed than the horizontal,and the damage of the structure is mainly controlled by the vertical damage.