Ultra-low frequency vibration control of urban rail transit: the general quasi-zero-stiffness vibration isolator

More intensive vibration reduction measures are necessary given increasing demands for urban rail transit vibration control. While the floating slab track system remains the most effective vibration isolation measure, a large vibration reduction blind area can still be observed at low frequencies. In the present study, a general quasi-zero-stiffness vibration isolator (GQZS vibration isolator) was proposed to enhance the ultra-low frequency (< 20 Hz) vibration control capability of floating slab tracks. The dimensionless analysis was utilised to design nonlinear stiffness curves and to determine the proposed GQZS vibration isolator static mechanical performance. Analyses of the dynamic mechanical behaviours of the proposed vibration isolator were conducted based on the force transmissibility rate. Results showed that the designed stiffness curve effectively reduced force transmissibility at low frequencies. A vehicle-floating slab track-substrate coupled dynamic model was proposed considering complicated train loads, and the results were consistent with force transmissibility analyses. When compared with conventional linear steel spring vibration isolators, the proposed GQZS vibration isolator significantly enhanced the floating slab track vibration reduction performance at ultra-low frequencies without affecting the driving stability or safety.