Analysis On The Dynamic Characteristics Of The Track Transition Of Typical Metro Track Systems

To mitigate the impact on the vibration-sensitive wayside areas, different kinds of vibration-reduction tracks are applied in a single subway line to satisfy the requirements of environmental evaluation and sTable operation. However, at the transition section between two tracks with different structure, stiffness and vibration degree, the abrupt change of the track stiffness will lead to higher dynamic load, which might cause unsTable operation or broken rails, etc. Based on previous studies, in this paper, four kinds of track models have been established by the finite element analysis, including general track, GJ-III fastener track, rubber damping pad floating slab track and steel spring floating slab track. According to the field test of a certain city metro, this paper analyzes the vibration and dynamic performance of the track transitions from the perspectives of vibration transmission and dynamic response. Taking the metro track parameters in the measured city as reference, three vertical dynamics models of the transition sections are established, namely, the transitions between general track and GJ-III fastener track, general track and rubber damping pad floating slab track, and general track and spring-steel floating slab track. Also, when a60km/h B-type vehicle passing by the transition sections, the relationship between the vertical vibration acceleration of the vehicle, the vertical displacement of the rail, the vertical acceleration of the rail, the wheel/rail vertical force, and the length of the transition section, the stiffness of the track are analyzed, taking the Sperling stability index is as one of the indicators to check the arrangement of the track transition sections. The analysis and conclusions are as follows:(1) According to the theoretical analysis and the measured data, it shows that: When the vibration frequency is less than500Hz, vibration reduces layer by layer on the same track. As for different tracks, the variations of vibration under different frequency are directly reflected on the rails.As for the general track and GJ-III fastener track, the vibration amplitude on the rail is obviously larger than that of track slab and the tunnel foundation; as for the rubber damping pad floating slab track and spring-steel floating slab track, the vibration amplitude on the rail and track slab is larger than that of the tunnel foundation.The vibration amplitude of rubber damping pad floating slab track and steel spring floating slab track slab is larger than that of general track and the GJ-III fastener track due to different track structures.The maximum vibration gap between general track and GJ-Ⅲ fastener track, rubber damping pad floating slab track and steel spring floating slab track is12dB,13dB and26dB respectively.(2) It is suggested by the results that a transition section should be set between the25m-long steel spring floating slab and the common rail, and the suggested length is10-15m. In the section, the steel springs can be laid out vertically with a-third increased density, normal spacing, and stiffness2times that of the A steel spring5.3kN/mm.As for the transition section between general track and rubber damping pad floating slab track, the stiffness increase of the rubber damping pad have more impact on the track system than the dynamic response of the vehicle. With a stiffer rubber damping pad, the vibration in the transition section will become weaker.The stiffness difference between the general track and GJ-III fastener track makes it necessary to set the stiffness transition section, which can be completed by rails with stiffness of25kN/mm.