Dynamic Analysis Of Rubber Bearing Floating Slab Track System On U-beam In Metro Elevated Line

U-beam is widely used in more and more metro elevated lines because of its lightweight structure,good sound insulation effect,high system integration efficiency and low construction and operation cost.Vibration and noise problems caused by metro operation are particularly prominent in elevated lines.In order to solve this problem,a variety of damping tracks are adopted in metro engineering design.In this paper,the coupled vibration characteristics of a rubber bearing floating slab track-U beam system in a metro project was studied in order to guide the track and bridge design of metro project.Firstly,the metro vehicle-track-bridge vertical coupled dynamic model was established based on the vehicle-track-bridge dynamic interaction theory.In the dynamic model,the vehicle submodel and the wheel-rail interaction submodel were programmed with the parametric design language APDL.The track and bridge were simulated by finite element method.The wheel and rail were coupled by wheel-rail force and wheel-rail displacement.The numerical integration method was hybrid explicit-implicit.Then,the vibration characteristics of vehicle-track-bridge system under the speed of 100km/h was calculated and analyzed.The results show that the dynamic responses of floating slab track,such as the wheel-rail vertical force,rate of wheel load reduction,the vertical deflection of bridge and the vertical acceleration of bridge,are reduced than that of integrated bed,and the decreasment of the vertical acceleration of bridge even reaches 80%.The vertical displacement of rail and floating slab exceed the limit when the vehicle reaches the maximum axle load.The vibration damping effect of the rubber bearing floating slab track is 9.7dB.It has a good vibration damping effect for the vibration of 20 Hz and above,and the vibration amplification phenomenon occurs in the frequency range of 8-16 Hz.In the same direction of the bridge,the vibration acceleration of the bottom plate is the largest,followed by the web plate,the vibration acceleration of the flange plate is the smallest.The U-beam is asymmetric structure,so the vertical acceleration of the left plates are smaller than that of the right plates.Finally,the effects of passenger load,driving speed,fastener stiffness,aging of rubber bearing and laying method of floating slab on the vibration characteristics of vehicle-trackbridge system were discussed.The results show that passenger load mainly affects wheel-rail force and system displacement responses,but has little effect on acceleration responses and vibration damping effect of floating slab.The increase of passenger load will slightly increase the low-frequency vibration of bridge below 10 Hz.When the vehicle speed increases,the wheel-rail force and the system acceleration responses present an increasing law.When the vehicle speed is 100 km/h,the vibration damping effect of the floating slab track reaches the maximum.Then,the vibration damping effect decreases continuously with the increase of the vehicle speed.With the increase of fastener stiffness,the vertical wheel-rail force,rate of wheel load reduction,the vertical acceleration of floating slab and bridge increase,and other dynamic indexes decrease.Fastener stiffness has a great impact on medium-high frequency vibration above 50 Hz.The greater fastener stiffness,the more disadvantageous to acceleration damping of bridge,and combined with the control of the vertical displacement of rail,the fastener with vertical static stiffness of 30-40 kN/mm should be adopted for the floating slab track.In the aging process of rubber bearing,the vertical displacement of rail and floating slab decreases,the vertical acceleration of bridge increases linearly,and other dynamic responses change little.With the increase of rubber bearing stiffness from design value to 1.4 times of design value,the vibration damping effect of floating slab track decreases from 9.7dB to 8.4dB,with a reduction rate of 13%,which can still meet the expected vibration damping requirement.Under the two kinds of floating slab laying schemes,the difference of dynamic responses amplitude at the beam end of track-bridge system is not more than 3%,and the track smoothness is good.