Research On Vibration Characteristics Of Overhead Contact System Portal Structure When Freight Train Runs On Dashaping Bridge

The Dashaping Bridge is located in the Lanzhou hub section of the newly built railway from Lanzhou to Chongqing.When there are freight trains passing through the bridge,the long-term vibration of the bridge itself and the shaking of the overhead contact system cause problems such as loosening,breaking,and falling off of the connecting bolts of the portal structure,as well as breaking of the hanging strings.These problems cause the contact line to swing greatly,affecting the pantograph flow and resulting in the vehicle being only able to run at a limited speed.This paper takes the portal structure of the overhead contact system on the Dashaping Bridge as the research object and studies the vibration characteristics of the portal structure.Through on-site detection of the hard span,the real-time data of the portal structure vibration is obtained and compared with the simulation results.A curved beam portal structure is designed and studied under the same special conditions,and finally,the dynamic characteristics of the two beams are compared and studied.(1)On the basis of structural dynamics,the static characteristics of overhead contact system portal structure are calculated,and the distribution of beam stress and bending moment is obtained.The calculation model of overhead contact system portal structure on four-line bridge is derived.Through modal analysis,the most basic vibration modes of overhead contact system portal structure are longitudinal and lateral vibration of portal structure pillar with small amplitude.Secondly,vertical vibration;The beam exhibits torsional vibration when the frequency of natural vibration is higher.(2)The portal structure simulation model of bridge-net is established.The portal structure vibration characteristics of vehicle under dynamic load were studied.As the speed of the truck on the continuous bridge increases,so does the speed.The moment shear force of overhead contact system line across the overhead contact system line is mainly concentrated in the overhead contact system column,and the other positions are small.The maximum displacement deformation is mainly concentrated in the beam span.It can be seen from the simulation analysis that the mid-span deflection and stress of overhead contact system are the largest when the truck runs at about 120km/h.(3)On-site portal structure vibration reduction measures are implemented by adding equipment beams,increasing equipment crossbeams,and diagonal support between equipment crossbeams and pillars to reduce beam vibration.The effectiveness of the on-site reinforcement optimization measures is verified through finite element simulation.Finally,by comparing the original state with the reinforced portal structure,the shear force,bending moment,displacement,and dynamic stress produced by the reinforced beam are significantly decreased,with a peak amplitude of the decrease of approximately 25%.(4)Real-time vibration detection of the working state of the portal structure is carried out using an automation and information detection system,which promptly detects the vibration data of the beam on-site.By comparing the vibration amplitudes obtained from finite element simulation and experimental vibration data collected under dynamic loads on-site,it can be determined that the contact line vibration is caused by the rapid passage of vehicles over the bridge,leading to torsional resonance of the portal structure and the eventual breaking of some of the hard span bolts of the overhead contact system.(5)A curved beam portal structure is designed under the same special conditions,and the Midas Civil finite element software is used to establish a model of the curved beam portal structure,and simulate and calculate the bending moment,displacement,and stress values of the curved beam under dynamic loads.The dynamic characteristic values of the two beams are compared under different working conditions,and the dynamic characteristic values produced by the curved beam hard span show a significant decrease,with a peak amplitude of the decrease of approximately 23%.