Zhi-ping Zeng’s research while affiliated with Central South University and other places

In order to accommodate higher speeds, heavier axle weights, and vibration damping criteria, a new floating slab structure was proposed. The new type of floating slab track structure was composed of three prefabricated floating slabs longitudinally interconnected with magnesium ammonium phosphate concrete (MPC). This study investigated the dynamic performance of the structure. We constructd a full-scale indoor experimental model to scrutinize the disparities in the impact performance between a longitudinally connected floating slab track and its longitudinally disconnected counterpart. Additionally, a long-term fatigue experiment was conducted to assess the impact performance of longitudinally connected floating slab tracks under fatigue loading. The findings are described in the following. 1) The new structure effectively suppresses ground vibrations, exhibiting a well-balanced energy distribution profile. However, the imposition of fatigue loading leads to a reduction in the damping performance of the steel spring damping system, thereby reducing its capacity to attenuate structural vibrations and leading to an increase in ground vibration energy; 2) After 107 loading cycles, the attenuation rate of the vibration acceleration for the MPC increases by 171.9%. Conversely, at the corresponding disconnected location, the attenuation rate of ground vibration acceleration decreases by 65.6%. In conclusion, longitudinally connected floating slab tracks exhibit superior vibration reduction performance. While the vibration reduction performance of longitudinally connected floating slab tracks may diminish to some extent during long-term service, these tracks continue to meet specific vibration reduction requirements.

To study the damping effect of different track structures on the environmental vibration, field tests of train-induced vertical acceleration were performed on four types of track structures, namely, ordinary track (OT), medium vibration-damping fastener track (MVDFT), floating-ladder track (FLT) and steel-spring floating slab track (SSFST). The measurement points were set on the rails, track slabs, and tunnel walls. Eventually, the time domain, frequency domain, and one-third- octave frequency division vibration level were adopted to investigate the vibration characteristics of four track structures. The results were obtained as follows. (1) The root-mean-square acceleration values of the four track structures at different measurement points were analyzed in the time domain. Overall, the results could not effectively reflect the damping capacity of the vibration-reduction measures. (2) Based on the one-third octave frequency analysis, regarding 10À6 m/s2 as the decibel reference value, we found that three vibration-reduction measures' vertical vibration level of the tunnel wall was significantly lower than that of OT. Specifically, the damping effect of SSFST was the most obvious. The Z-weighted vibration levels of the three vibration-reduction measures on the tunnel wall have been reduced by 8.919, 11.745 and 13.744 dB, respectively. (3) According to the results of the vibration-transmission characteristics in the frequency domain, the main vibration-frequency regions of the four track structures at the track slab and tunnel wall were all in the range of 1 to 20,00 Hz. Concerning OT, MVDFT, FLT, and SSFST, the peak values of the vibration transmission from the rail to the tunnel wall sequentially decreased, and the damping effect sequentially increased. This paper compared the damping capacity of the above four track structures at 1 to 80 Hz according to ISO 2631-1. In addition, their more detailed vibration characteristics at 1 to 2000 Hz were also considered. It aims to provide a more comprehensive study for the application of subway vibration-reduction measures.

Background: In order to study the applicability of Low Vibration Track (LVT) in heavy-haul railway tunnels, this paper carried out research on the dynamic effects of LVT heavy-haul railway wheels and rails and provided a technical reference for the structural design of heavy-haul railway track structures. Methods: Based on system dynamics response sensitivity and vehicle-track coupling dynamics, the stability of the upper heavy-haul train, the track deformation tendency, and the dynamic response sensitivity of the vehicle-track system under the influence of random track irregularity and different track structure parameters were calculated, compared and analyzed. Results: Larger under-rail lateral and vertical structural stiffness can reduce the dynamic response of the rail system. The vertical and lateral stiffness under the block should be set within a reasonable range to achieve the purpose of reducing the dynamic response of the system, and beyond a certain range, the dynamic response of the rail system will increase significantly, which will affect the safety and stability of train operation. Conclusions: Considering the changes of track vehicle body stability coefficients, the change of deformation control coefficients, and the sensitivity indexes of dynamic performance coefficients to track structure stiffness change, the recommended values of the vertical stiffness under rail, the lateral stiffness under rail, the vertical stiffness under block, and the lateral stiffness under block are, respectively 160 kN/mm, 200 kN/mm, 100 kN/mm, and 200 kN/mm.

In this paper, a train-track-bridge coupled dynamics modeling and coupling method was proposed. The coupled dynamic system was modeled separately with multiple subsystems by finite element method and the three-dimensional nonlinear wheel-rail contact relationship was used to account for non-linearity. Using explicit numerical methods and coupling the subsystems by the load term on the right end of the dynamic equations, repetitive iteration in the dynamic response solution process was avoided. Thus, a simplified the solution of nonlinear dynamic models can be achieved in limited time. In order to meet the requirement of diagonalization of the mass matrix in the algorithm, the modal superposition method was adopted. In the solution method proposed in this study, only a set of mass, damping, and stiffness matrices of the subsystem structure need to be established for solution instead of building the total matrix of the coupled dynamic system. Thus, greatly reduce the dynamic system matrix dimension for periodic train-track-bridge coupled dynamic systems. The train-track-bridge coupled dynamics model proposed in this paper is suitable to model various track and bridge structures, the wheel-rail contact relationship used is closer to reality and has more accuracy in describing the force state between wheel and rail. Besides, the unit size, number of modalities and numerical integration step size required in the calculation of each subsystem have been determined based on numerical experiments. Using the established dynamics model, the effects of the commonly used bound and separation ballastless track structures on the train operation safety was analyzed employing single-sample and multi-samples analysis. The calculation results demonstrated that the separation model is preferable for the prediction of train operation safety.

To further explore the fatigue characteristics of the CRTS (China Railway Track System) type III slab ballastless track structure generally used for high-speed railways, the fatigue damage of CRTS III type slab ballastless track structure system under the action of heavy-haul trains was studied. Based on the three-stage model, the CRTS III slab ballastless track structural system fatigue finite element numerical model was established, with particular emphasis on the fatigue characteristics of the self-compacting concrete of the CRTS III slab ballastless track under a load of heavy haul trains. To verify the reliability of the established model, the track structure displacement and stress under static load and fatigue load were analyzed and compared. The results shows that the model can be used to explore the fatigue damage law of the structural system of the CRTS III slab ballastless track under the action of heavy-haul trains. The results of further analysis showed that: (1) For self-compacting concrete, the maximum longitudinal tensile stress is greater than the maximum lateral tensile stress (2) For the longitudinal direction of the lower surface of the self-compacting concrete, once the tensile stress reaches the tensile strength of concrete, the self-compacting concrete cracks; as the number of fatigue loads further increases, more cracks will develop from the sides of the slab centre in the self-compacting concrete (3) The larger the axle load, the higher the stress level of each layer of the track structure, the faster the concrete damage rate, and the earlier the concrete cracks. As axle load is greater than 35 t, the damage of self-compacting concrete is more pronounced.

Compared with ordinary railways, the curve radius of tram lines tends to be smaller, with minimum values of only 30 m. Therefore, wheel–rail interaction is more intense and complicated in sections of small radius tram line curves. Using a stochastic variable sample set based on a generalized probability density evolution method, the stochastic variable–spectrum representation method was used to generate a time-domain sample set of stochastic track irregularities. By inputting the stochastic set of track irregularities into a tram-track coupled dynamic system model, the stochastic dynamic response of the coupled dynamic system can be obtained. Moreover, by substituting the stochastic dynamic system response into the generalized probability density evolution formula, the process of probability density evolution of each evaluation index can be obtained by the finite difference method. Finally, the dynamic response of the tram-track coupled dynamic system can be evaluated by the probability distribution of each index. By setting a series of specific groove rail wear values, a tram-track coupled dynamic analysis was carried out, and compared with the specification requirements, vehicle safety limits under different wear values were obtained. This research has great engineering value for guiding the routine maintenance of small radius curve sections of trams.

This paper presents a vehicle operation safety evaluation model; to this end, a nonlinear vehicle-track coupled dynamic system stochastic analysis model under random irregularity excitations based on probability density evolution method was developed. The nonlinear coupled vehicle-track dynamic system is used to accurately describe the wheel-rail contact state. The stochastic function-spectral representation is used to simulate the random track irregularity in the time domain for the first time; consequently, the frequency components in the irregularity are preserved and random variables are reduced. In the process of evaluating the safety of train operation, the probability evolution, reliability of evaluation indices for different limit values, and evaluation indices for different probability limits are calculated for more accurate evaluation. The dynamic model and safety evaluation method was verified using the Zhai-model and Monte Carlo method. The results show that, when the probability guarantee is increased, the running safety index of the vehicle increases more rapidly with running speed and the left/right wheel-rail derailment coefficient increases rapidly at running speeds above 400 km/h. The computational model provides a novel direction for vehicle operation safety evaluation.

The rails at the transition between a bridge or subgrade and a tunnel tend to creep longitudinally because of a temperature gradient on the rail, which can cause irregularity in the track. The longitudinal temperature distribution along the rail and the longitudinal resistance of the fasteners are the main influences on rail creep. In this paper, the linear and nonlinear models of longitudinal temperature distribution on rails and the longitudinal resistance of fasteners are tested for their accuracy in predicting rail creep. By researching the rail at the temperature-transition zone, differential equations for the longitudinal displacement and force of the rail are established. To predict the changes that a rail will experience in a temperature-transition zone, expressions for the longitudinal displacement and force are derived from these differential equations. The derived calculation scheme is tested for three conditions: linear models of both rail temperature and longitudinal resistance, linear rail temperature and nonlinear resistance, and nonlinear models of both rail temperature and displacement. The maximum longitudinal rail displacement and the maximum longitudinal additional force in all three conditions are compared to reveal the influence of the maximum temperature force gradient multiple and the maximum fastener resistance on longitudinal displacement.

A three-dimensional rail-bridge coupling element of unequal lengths in which the length of the rail element is shorter than that of the bridge element is presented in this paper to investigate the spatial dynamic responses of a train-track-bridge interaction system. Formulation of stiffness and damping matrices for the fastener, ballast, and bearing, as well as the three-dimensional equations of motion in matrix form for a train-track-bridge interaction system using the proposed element are derived in detail using the energy principle. The accuracy of the proposed three-dimensional rail-bridge coupling element is verified using the existing two-dimensional element. Three examples of a seven-span continuous beam bridge are shown: the first investigates the influence of the efficiency and accuracy of the lengths of the rail and bridge elements on the spatial dynamic responses of the train-track-bridge interaction system, and the other two illustrate the influence of two types of track models and two types of wheel-rail interaction models on the dynamic responses of the system. Results show that (1) the proposed rail-bridge coupling element is not only able to help conserve calculation time, but it also gives satisfactory results when investigating the spatial dynamic responses of a train-track-bridge interaction system; (2) the double-layer track model is more accurate in comparison with the single-layer track model, particularly in relation to vibrations of bridge and rail; and (3) the no-jump wheel-rail interaction model is generally reliable and efficient in predicting the dynamic responses of a train-track-bridge interaction system. © 2016, Brazilian Association of Computational Mechanics. All rights reserved.