Time-domain Analysis On Buffeting Response Of Long-span Suspension Bridge Considering Unsteady Characteristics Of Fluctuating Wind

With the continuous development of bridge construction in the direction of long-span and softness,the stiffness of bridge structures is getting smaller and smaller,and the problem of wind-induced vibration is becoming more and more prominent.Wind-resistant design has become an indispensable part of bridge design.Among them,buffeting response calculation is a hotspot in the research of bridge wind vibration problems.Most of the relevant studies regard the fluctuating wind speed that causes buffeting as a stationary random process.However,in recent years,measured data have shown that the fluctuating wind in the area of bridges exposed to complex wind environments has strong non-stationary characteristics.Traditional chattering analysis ideas can no longer meet the needs of practical engineering.Therefore,it is of great significance to study the buffeting response of long-span bridges under the action of non-stationary fluctuating wind for bridge wind resistance and disaster reduction engineering.This paper adopts the research method of numerical simulation,based on a long-span suspension bridge located in the coastal area of China,and carries out the research on the nonstationary buffeting response of the bridge under the condition of considering the nonstationary characteristics of fluctuating wind.The specific work content is as follows:(1)Based on the evolutionary spectrum theory,the non-stationary fluctuating wind in the bridge site area was simulated by using the harmonic synthesis method,and the simulation results were tested from the perspective of power spectrum and turbulence degree,and compared with the simulation results of the steady fluctuating wind field.The research shows that the simulated non-stationary fluctuating wind speed has the characteristics of time-varying variance,the power spectrum test results are highly consistent with the target spectrum,the turbulence degree is smaller than the simulated steady fluctuating wind speed turbulence degree under the same parameters and meets the requirements of the wind resistance code that the downwind turbulence degree is about twice the vertical relationship,and generally can be used as a source of fluctuating wind field data for bridge non-stationary buffeting response calculations.(2)The finite element model of the long-span suspension bridge was established and the dynamic characteristics of the structure were analyzed.Based on the bridge non-stationary buffeting analysis theory,the non-stationary wind speed was transformed into non-stationary wind load,the time-domain processing and loading method of the load were studied.The research results show that the first-order natural frequency of the bridge is 0.06973 Hz,and the corresponding vibration mode characteristic is symmetrical side bending of the main beam.When applying wind load to the model,it is necessary to treat the load into three parts: static wind load,non-stationary buffeting force load and aerodynamic self-excited force.The static wind load is loaded on the unit nodes by the centralized method after coordinate transformation.The time-domain processing of non-stationary buffeting force loads based on unsteady assumptions can be done by using the equivalent wind spectrum method.The pneumatic selfexcitation force is realized by the Matrix27 unit provided by the finite element analysis platform.(3)Based on the numerical wind tunnel,the necessary aerodynamic parameters of the main girder section in the analysis of the bridge buffeting response were identified,combined with the previous work results,the time domain analysis of the non-stationary buffeting response of the long-span suspension bridge was carried out,and the effect of different factors on the buffeting response of the bridge was studied.The research results show that: the nonstationary chattering displacement response of the main girder is greater than that of the bridge tower,and the maximum response position of the transverse bridge direction and torsion is in the mid-span and the vertical maximum response position is near the 1/4 span;The peak buffeting internal force at the tower bottom of the bridge tower is relatively large,but there is no wind-induced displacement response at this place;the change of the incoming wind angle of attack has a significant impact on the buffeting displacement response of the main beam but has little effect on the bridge tower;Compared with the self-excited force,the aerodynamic admittance attenuates the buffeting displacement response of the bridge to a greater extent.When the two act together,the peak buffeting internal force of each section of the bridge is greatly reduced and the displacement response is correspondingly weakened.