Study On Vibration Induced By Idle Speed Of Continuous Girder Bridge Under Heavy Traffic Congestion

The dynamic response of vehicle-bridge coupled vibration of bridge structure under vehicle load is one of the important directions of bridge research at present.Especially when heavy-duty vehicles are congested on the bridge,the impact effect of the vehicle engine idling vibration as the excitation source on the bridge has not been paid attention to.In the "2015 General Specification for Bridges and Culverts",the consideration of the impact coefficient is the impact effect of the vehicle vibration on the bridge during the movement of the car,and only the fundamental frequency of the structure is considered as the only factor,and no heavy-duty vehicles are congested on the bridge.,The impact effect of the idle speed as the excitation source on the bridge.Therefore,the study on the effect of idling-speed excitation of congested heavy vehicles on the bridge has important theoretical significance and engineering practical value.This paper takes the Shizuishan Yellow River Highway Bridge as the backing project.The main work and conclusions are as follows:1.Based on the investigation and statistics of the traffic flow of the overburden control and detection station of Shizuishan Yellow River Highway Bridge,the traffic flow data of three peak hours are summarized,five vehicle load models of the bridge are put forward,and 10 models of congestion idle speed are drawn up.Finally,the vehicle motion equations of the typical light vehicle and the typical heavy vehicle are established,and then the mass matrix,damping matrix and stiffness matrix of the corresponding vehicle are deduced.2.The overall structural dynamics model of the full bridge of the Shizuishan Yellow River Highway Bridge was established by Midas civil finite element software,and the dynamic characteristics of the full bridge were obtained.Finally,in the Midas civil finite element software,the vehicle congested idling coupled vibration was established through the contact points of the vehicle tires and the bridge deck.The finite element model gives the dynamic characteristics of the full bridge after the heavy vehicle train is coupled with the bridge.3.Considering the four influencing factors of the congested vehicle load,the distance between the congested vehicles,the idling frequency of the car engine and the congestion condition of the vehicle,the displacement and stress at the middle span of the first span and the second span of the bridge and the displacement and stress at the top of the pier are compared.Analysis;On this basis,the magnification coefficients under the respective influencing factors are calculated and analyzed separately,and compared with the impact coefficients obtained according to the calculation formula in the "2015 General Specification for Bridges and Culverts".The research results show that,on the whole,for the long-span prestressed concrete continuous girder bridge supported by the study,the dynamic coefficient of the bridge under the idling state of heavy traffic congestion is greater than the impact coefficient calculated according to the code.When the load of the congested heavy truck and train changes,the obtained mid-span stress amplification factor increases first and then decreases with the increase of the load weight.When the heavy truck is fully loaded,the mid-span stress amplification factor reaches the maximum value.In the range of 1.0m ～4.0m,the mid-span stress amplification factor decreases gradually with the increase of the congestion distance between heavy vehicles and trains,and tends to be stable in the range of 3.0m ～ 4.0m.In the range of 600r/min to 800r/min,with the increase of engine idle frequency,the calculated mid-span stress amplification factor firstly increases and then decreases.When the idle frequency is 700r/min,the mid-span stress amplification factor reaches the maximum value.The displacement amplification coefficient and the stress amplification coefficient obtained by the change of the phase difference of the sinusoidal function of the congested heavy train have no significant change,indicating that the change of the phase difference cannot have a significant impact on the vehicle-bridge system.Due to the variety of the parameter of congestion condition,the obtained amplification coefficient is irregular to follow,and further research is needed.