Dynamic Response Of Track Structure Research Articles

Static and dynamic response characteristics of a ballastless track structure of a high-speed railway bridge with interlayer debonding under temperature loads

The ballastless track structure of a high-speed railway (HSR) undergoes interlayer debonding during its service due to train loads, environmental loads, and construction. A CRTS Ⅱ ballastless track slab structure is a longitudinally-continuous reinforced concrete structure, and the temperature load is a major factor in the occurrence of interlayer debonding. However, the effect of temperature loads on the static and dynamic response of the CRTS Ⅱ ballastless track structure of an HSR bridge following interlayer debonding is unknown. This study established a finite element simulation model of a ballastless track structure over a bridge and a vertically-coupled dynamic vehicle–track–bridge simulation model. The deformation generated by the track structure at temperature loads was inputted as track irregularity to the dynamic simulation model, and the change laws of the deformation and dynamic response of the track structure under different temperature loads was studied. The results showed that under different temperature loads, the ballastless track slab first undergoes longitudinal deformation, followed by transverse deformation. On this basis, the dynamic response of the HSR ballastless track structure over a bridge with interlayer debonding was found to increase with increasing temperature loads, while the frequency band changed from single to complex. This study not only provides insights into the effects of temperature loads on track structure damage, but also lays a theoretical foundation for the development of maintenance and repair plans for railroad departments.

Dynamic Responses of Ballastless High-Speed Railway Due to Train Passage With Excitation of Uneven Trackbed Settlement

The ballastless slab track has been widely used in newly-developed high-speed railways in China as well as in other countries for its high stability and low maintenance. However, loss of track vertical alignment due to uneven trackbed settlement will bring adverse impact on train’s running safety and track serviceability. In this study, a train-track-trackbed coupling model has been proposed to investigate the dynamic responses of track structure with the excitation of trackbed settlement with varied patterns. To validate the proposed analysis model, comparisons with both the analytical solution and in- situ measures have been performed. The influences of train speeds, settlement trough amplitude and length are discussed based on this analysis model. It’s indicated that the dynamic responses of train vehicle and track structure increase with increasing in train speed and settlement amplitude within certain settlement length. By introducing the standards for train operation safety and riding comfort, a new trackbed settlement control criteria is proposed. The computation results indicate that the standard for train operation safety is found to be the dominating factor for uneven settlements with the length less than 10 m, while the standard for riding comfort dominates the settlement control criteria in other cases. To further facilitate the settlement control criteria in engineering practices, the ratio of settlement amplitude and settlement length (which is defined as deflection ratio) is adopted to depict the envelop curves for various settlement patterns.

Study on the interlayer debonding and its effects on the mechanical properties of CRTS II slab track based on viscoelastic theory

In this study, a novel viscoelastic finite element model of China Railway Track System (CRTS) II slab track incorporating viscoelastic parameters and a cohesive zone was established. Based on this model, the interlayer debonding between the prefabricated concrete slabs and the cement asphalt mortar layer and its effects on the mechanical performance of track structure were systematically investigated. Firstly, the validity of the viscoelastic model was verified by comparing the simulated results with experimental data. Then, the initiation mechanism of debonding under temperature gradient loading and under coupling actions of temperature and dynamic vehicle loadings was analyzed and then compared with that based on a common elastic model. Finally, typical interlayer debonding cases with different locations and sizes were purposely set up and their effects on the vertical stresses and vertical displacements of the track were discussed. Results show that after introducing viscoelastic parameters, the maximum opening height and the extension width of debonding increase rapidly, while the temperature gradients of initiating debonding keep unchanged but the penetration temperature gradients significantly decrease. On the other hand, the vertical stresses and vertical displacements of track structure are hardly affected by the debonding in the middle, slightly changed by the debonding length at the edge and significantly affected by the debonding width at the edge. With the increase of debonding area, the vertical stresses and vertical displacements significantly increase, especially when the debonding area is larger than critical values. Compared to the elastic model, the use of the viscoelastic model leads to larger vertical stresses and displacements. It is believed that the incorporation of viscoelastic parameters effectively enhances the performance of FEM, which can better predict the initiation of interlayer debonding and the dynamic response of track structure.

Study on dynamic response of track structures under a variable speed moving harmonic load

Basing on the dynamic response characteristics of the periodic structure under a moving harmonic load in frequency domain and the superposition principle, the dynamic response of track structure under variable speeds moving harmonic load is investigated. Firstly, the track is simplified as an Euler beam model periodically supported by continuous discrete point, the dynamic differential equation of vertical vibration for the track structure is formulated. Secondly, for convenience of analysis, the analytical expression for the amplitude-frequency response of any point on the track structure under the moving harmonic load is derived in frequency domain. Based on the theory of the infinite periodic structure, the dynamic responses of the track structure under the variable speed moving harmonic load are analyzed theoretically. Finally, the influences of velocity and acceleration on the dynamic response of track structure are numerically analyzed in detail. The research results indicate that the amplitude-frequency response peaks of the track under moving harmonic load with variable and constant speeds occur near the excitation frequency. The displacement response of the track increases slightly with increase of the acceleration, and the variation trend of dynamic response is basically similar. The vibration displacement response of the rail can be effectively improved by increasing the initial velocity of the moving harmonic load, while the peak value of amplitude-frequency response remained constant.

A 2.5D finite element approach for predicting ground vibrations generated by vertical track irregularities

Dynamic responses of track structure and wave propagation in nearby ground vibration become significant when train operates on high speeds. A train-track-ground dynamic interaction analysis model based on the 2.5D finite element method is developed for the prediction of ground vibrations due to vertical track irregularities. The one-quarter car model is used to represent the train as lumped masses connected by springs. The embankment and the underlying ground are modeled by the 2.5D finite element approach to improve the computation efficiency. The Fourier transform is applied in the direction of train’s movement to express the wave motion with a wave-number. The one-quarter car model is coupled into the global stiffness matrix describing the track-ground dynamic system with the displacement compatibility condition at the wheel-rail interface, including the irregularities on the track surface. Dynamic responses of the track and ground due to train’s moving loads are obtained in the wave-number domain by solving the governing equation, using a conventional finite element procedure. The amplitude and wavelength are identified as two major parameters describing track irregularities. The irregularity amplitude has a direct impact on the vertical response for low-speed trains, both for short wavelength and long wavelength irregularities. Track irregularity with shorter wavelength can generate stronger track vibration both for low-speed and high-speed cases. For low-speed case, vibrations induced by track irregularities dominate far field responses. For high-speed case, the wavelength of track irregularities has very little effect on ground vibration at distances far from track center, and train’s wheel axle weights becomes dominant.

Comparison on General Track Spectrum for Chinese Main Railway Lines and Track Spectrum of American Railway Lines

The general track spectrum of Chinese main railway lines (ChinaRLS) and the track spectrum of American railway lines (AmericaRLS) are compared in terms of character of frequency domain, statistical property of time domain samples and dynamic performance. That the wavelength range of the ChinaRLS, which is characterized by the three levels according to the class of railway line, is less than AmericaRLS at common wave band of 1~50m is calculated. Simultaneously, the mean square values of two kinds of track spectra are provided at the detrimental wave bands of 5~10m, 10~20m, and so on. The time-histories of ChinaRLS and AmericaRLS are simulated according to the trigonometric method, and the digital statistical nature of simulated time samples is analyzed. With inputting the two kinds of time-histories into the vehicle-railway system, the comparative analysis of the two kinds of dynamic performances for ChinaRLS and AmericaRLS is done in terms of car body acceleration, rate of wheel load reduction, wheel/rail force, and the dynamic responses of track structure. The result shows that ChinaRLS can characterize the feature of the Chinese track irregularity better than AmericaRLS, the track irregularity with the ChinaRLS of 200km/h is superior to the AmericaRLS, and the track irregularity with the ChinaRLS of 160km/h corresponds to with the sixth of AmericaRLS.