Weining Liu

Dynamic displacement response of track subjected to a load moving at a variable speed

A closed-form displacement response of track subjected to loads moving at variable speeds is proposed in this paper. The structure of the track is modeled as a Timoshenko beam of infinite length that is periodically supported by double-layer spring-damping elements. The frequency-domain displacement response of the track is simplified into the mathematical form of a summation rather than an integral. The transfer function for the track is expressed in the form of a transfer matrix. Various kinds of moving loads, such as single and series moving forces, masses and double-layer mass systems, are considered in calculations. For the verification of the theory, the displacement response of a simply supported beam subjected to masses moving at variable speeds is calculated and compared with reports in the literature on the same case. The obtained results indicate that the influence of the loads moving at variable speeds on the displacement response of the track cannot be ignored, and the displacement response of the track increases slightly with acceleration of the moving loads. Also, larger oscillations are generated by the interaction of the moving mass and the track.

An experimental study of vibration reduction of a ballasted ladder track

The ballasted ladder track is a new type of longitudinal track. In this paper, to investigate its vibration reduction effect, both a laboratory test and in situ experiment were conducted. As the vibration sources, a newly designed drop weight impulse setup was employed in the laboratory test, and moving metro trains were employed in the in situ measurement. The vibration reduction effects of the ballasted track with ladder sleepers and regular concrete sleepers were compared. The results show that the ballasted ladder track can effectively decrease the peak value in the time domain and has the potential effect to control the environmental vibration in low frequencies. The shape of the sleeper can induce changes in the vibration field of the ballast.

Dynamic response of a curved railway track subjected to harmonic loads based on the periodic structure theory

In this study, the authors have analysed the dynamic response of a curved railway track that is subjected to moving and non-moving harmonic loads. The track is considered as a curved Timoshenko beam supported by periodically spaced discrete fasteners. The displacement and rotation of the curved rail are expressed as the superposition of track modes in the frequency domain. Periodic structure theory is applied to the equations of motion of the curved track, allowing the dynamic response of the track to be calculated efficiently in a reference cell. The effect of the stiffness and damping of the fasteners, the fastener spacing and the radius of curvature on the mobility and decay rate of the track are analysed for non-moving loads on the rail head. The vibration of the rail due to moving loads is also discussed. It is found that the dynamic response of a curved rail with a large radius has the same characteristics as that of a straight track. However, the dynamic response of the track is significantly affected when the radius of curvature becomes small. The radius affects the mobility; it also has an effect on the track decay rate below 2000 Hz and the velocity of the rail in the vertical direction when the radius is smaller than about 15 m and for the lateral direction when it is less than about 30 m. Moreover, the curvature has a significant influence on the vertical/lateral cross mobility, the magnitude of which increases as the radius is reduced. When the radius is larger than 10 m, the amplitude of the lateral vibration under a moving vertical load and the vertical response to a moving lateral load are inversely proportional to the radius.

Prediction of Metro Train-Induced Vibrations on a Historic Building: The Case of the Round City and Chengguang Hall in Beijing

With the development of urban mass transit, the train-induced vibrations become a potential problem to historic buildings nearby. The protection and maintenance of historic buildings have aroused a great deal of public attentions. In this paper, the problem of environmental vibrations was analysed for the Round City and Chengguang Hall, a group of historic buildings in Beijing. The historic buildings are located close to a busy road and are near to a planning subway line. The natural frequencies and dynamic amplification factor of the timber structure were estimated by an empirical method. Then, a finite element model was built to predict the metro train-induced vibrations. The results show that, even if the floating slab track was used train-induced vibration can still be a potential problem against long-term protection for the timber structure.

Study on Evaluation Index of Environmental Vibration Induced by Urban Transit

Index to evaluate environmental vibration induced by urban rail transit are VLzmax and VLmax. Confused calculating methods of evaluation index have affected plan and design of subway line. Influence of overlapping coefficient and frequency weighting curve on VLzmax is researched in this paper. The study found that when the overlapping coefficient is 3/4, the result of VLzmax is stable basically. Frequency weighting curve in ISO 2631-1:1997 considering the effect of rail transit vibration on human health, comfort and perception, which is recommended for the amendments on the GB10070-88 Standard. Calculating methods of linear averaging, peak hold have significant influence on the VLmax result, which could affect the evaluating result. In order to ensure the reliability of evaluation results, peak hold method should be adopted as the calculating method.