Study On Vibration Isolation Performance Of The Floating Slab Track System In Mertro Lines

Floating slab track system is one of the most effective measures for mitigating ground-borne vibration induced by metro trains. It has been widely used in special districts which have strict vibration limitation required. The effectiveness of the floating slab track vibration isolation system is only achieved in reducing medium and high frequencies above ^1/22 times the resonance frequency of the track. While low frequency vibration propagates through the tunnel and surrounding soil into nearby buildings, causing much annoyance to inhabitants and malfunctioning to sensitive equipment. Therefore, it is important to expand the vibration isolation range and improve the vibration isolation performance by changing structural and dynamic parameters of floating slab track.Based on analytical approach and numerical simulation, the paper assesses vibration isolation effective and vibration isolation range of floating slab system. The main research works of this dissertation are as follows.(1) A comprehensive survey and generalization for vibration countermeasures is reviewed, and the basic principles and methods (analytical approaches, numerical simulation and field measurement) are discussed to illuminate necessary and aim of this research.(2) The vibration isolation mechanism of floating slab track is presented. Moreover, the design principles and criteria of the track are discussed.(3) A double-beam model on rigid foundation subject to a harmonic moving load is employed to assess vibration isolation performance of floating slab system. The track is assumed to act as infinitely long double Euler-Bernoulli beam on elastic foundation. By means of moving coordinate and Fourier transformation method, the differential equations of floating slab track system are established and solved in the wavenumber-frequency domain. The contour integration method is used to convert the responses of the track system from wavenumber-frequency domain into space-time domain. The results of transmitted force are obtained by MATALB software to assess vibration isolation effectiveness of the track with various parameters.(4) By means of ANYSY software, a dynamic finite element model of floating slab track system is developed to research the dynamic characteristic. In order to assess effects of the structural parameters (such as length, thickness of slab, etc.) and dynamic parameters (such as stiffness of railpads and bearing, etc.) on vibration isolation range, various parameters are calculated in the model. The result demonstrates that proper dynamic parameters of floating slab track choosen in design phase can improve vibration isolation range.(5) The contents are summarized and some questions on this subject which need to be deeply studied are put forward.