The effect of porous sound-absorbing concrete slabs on railway noise reduction is examined in this paper. First, the acoustical absorption coefficients of porous concrete materials with various aggregate types, gradations, fibre contents, and compaction indexes are measured in the laboratory. The laboratory results show that porous concrete that uses a composite of expanded perlite and slag as aggregate can not only obtain good acoustical absorption properties but also satisfy mechanical requirements. Also, the gradation of the combined aggregate has a significant effect on the acoustic absorption performance of the porous concrete, with an optimal aggregate gradation of 1~3 mm. Furthermore, the fibre content and compaction index affect both the strength and the acoustic absorption property of the porous concrete, with the optimum value of 0.3% and 1.6, respectively. Then, the findings from the laboratory studies are used to make porous sound-absorbing concrete slabs, which are applied in a test section. The measurements indicate that porous sound-absorbing concrete slabs can significantly reduce railway noise at different train speeds and that the amount of the noise reduction changes roughly linearly with speed when the train is traveling at less than 200 km/h. The maximum noise reduction is 4.05 dB at a speed of 200 km/h.

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.

Self-powered realization for synchronous switching circuits is a hot spot for piezoelectric vibration energy harvesting. Two typical kinds of switches, bi-polar junction transistor (BJT) or metal oxide semiconductor field effect transistor (MOSFET) are popularly used without a clear understanding about the performance difference. In this paper, comparative investigations about adopting these two types of switches based on a case study are performed. It is analyzed that the performance difference comes from three aspects: the gate parasitic capacitance, the turning-on threshold and the driven mechanism. In particular, the third one imposes a critical influence on the performance. Investigations are performed on the self-powered synchronous switching circuit of two possible methods: with electronic breakers or with external control units. The results from simulations and experiments show that the current-driven mechanism limits the available performance in the case of the BJT switch in comparison with the case of the MOSFET switch. The difference is especially obvious for the cases of large piezoelectric capacitance and open-circuit voltage. A preliminary design guideline is concluded that the MOSFET is probably a better choice with the same voltage and current ratings in most cases.

The extensive use of steel spring floating slab tracks has effectively addressed the challenge of alleviating the environmental vibrations induced by urban