Study On Train Induced Wind And Wind-induced Vibrations Of A Fly-over Steel Box Girder Cable-stayed Bridge Subjected To Under-passing Of High-speed Trains

In recent years,with the increase of train speed,the wind-induced vibration and comfort of pedestrian were concerned.The steel box girder bridge has lightweight,low stiffness,and small damping,so the aerodynamic force of the high-speed train may cause a larger vibration response of the bridge.Under this background,this thesis carried out a series of studies of characteristics of train induced wind and wind-induced bridge vibrations during the under-passing of high-speed trains.Firstly,the computational fluid dynamics software FLUENT is used to carry out the numerical simulation of a cross-line bridge at a station and compare it with the measured values to verify the reliability of the analysis method used in this paper.Furthermore,establish the flow field model of high-speed trains passing through the bridge,and the train induced wind characteristics are analyzed.On this basis,analyze the characteristics of train induced wind and its variation rule under different influencing factors.Finally,based on the finite element software MIDAS/CIVIL2019,the dynamic responses of cable-stayed bridges during construction and operation are studied under these influencing factors.The main conclusions are as follows.(1)The wind pressure of plates and the three-component force of the beam sections show obvious "head wave" and "tail wave" effects.The disturbance of adjacent parts,the height from the track surface,and the distance from the train together affect the wind pressure distribution in different regions.The extreme value coefficient of the lift is exponentially related to the distance from the centerline of the track.Extreme values of wind pressure and lift force of each section have a quadratic relationship with the speed and a negative power exponential relationship with clearance under the bridge.As the intersection angle decreases,the lift amplitudes at both ends and mid-span of the beam are less affected,and the lift amplitudes at 1/4 span and 3/4 span are more affected.(2)Compared with the single-line operation,the extreme values of wind pressure and lift force under the bridge increased significantly.The extreme values of head wave positive pressure and tail wave negative pressure on the windward side are mainly controlled by train1,and the extreme values of head wave negative pressure and tail wave positive pressure are mainly controlled by train 2.In addition,the characteristics on the leeward side are contrary to them.The extreme lift in the range of the L5～R5 beam sections are about 1.7～2.5 times that of single-line operation.The influence of the distance between centers of lines on wind pressure and lift force of each beam section is not significant.(3)The law of construction stage and operation stage under the influence of different factors are the same.With the increase of the train speed,the vibration displacement of the beam is advanced,and the amplitude is basically on the rise.As the clearance under the bridge decreases and the intersection angle decreases,the vibration displacement value increases.(4)Within the value range of each influencing factor investigated in this paper,the positive reaction of temporary pier caused by train induced wind can be ignored compared with the maximum limit value.The negative reaction will not cause the temporary pier to empty.The vibration of the beam caused by the aerodynamic action of the train does not have a significant impact on the comfort of the pedestrian.