Dynamic Train Track Interaction Research Articles

Long-term freeze–thaw cycle behavior of high-speed railway embankment in frozen soil regions and its effects on train-track dynamic interaction system

The high-speed railway embankment built in cold regions has a long-term freeze–thaw cycle behavior, and the frost heave of soil will inevitably affect the smoothness of the track structure laid on the embankment, resulting in the deterioration of the train running performance and the dynamic behavior of the ballastless track system. This work is motivated by the research to investigate the long-term freeze–thaw behavior of the embankment in frozen soil regions and its effects on the train-track dynamic interaction system. Based on this motivation, the temperature-deformation field model of the embankment and the train-track dynamic interaction model (TTDIM) are established as an integrated model. The additional track irregularity triggered by the frost heave deformation of the embankment is regarded as the excitation source in the TTDIM to achieve the co-analysis of two sub-models. Through an illustrative example, the evolution characteristics of the freeze–thaw cycle behavior of embankment is fully revealed. Moreover, the effects of time-varying frost heave deformation of embankment on the performance of train-track interaction are quantified from the aspect of representative responses and safety evaluation indexes. This paper provides a valuable model and research thought reference for the analysis and assessment of the performance of train-track interaction under the long-term freeze–thaw cycles of the embankment in frozen soil regions.

Investigations on the Effects of Rail Longitudinal Forces in Train-Track Dynamic Interaction

Nowadays, attention to railways has been increased as one of the important transportation methods. Various factors can cause longitudinal forces on the railway tracks, so the most important factors are the temperature changes due to the rail contraction and expansion (thermal forces), train braking system forces and acceleration, etc. Increasing longitudinal force can lead to buckling phenomena in railway tracks. In this paper, the effects of tensile and compressive longitudinal forces on the parameters of rail, sleeper, and ballast layers under vertical moving loads are investigated by using the finite element method. In this regard, by performing sensitivity analyses for different values of longitudinal forces and train speeds dynamic responses (displacement, velocity, and acceleration) of railway track components like rail, sleeper, and ballast have been studied. The results show that increasing the values of longitudinal axial force from –2000 [kN] up to 2000 [kN] as well as increasing the train speed from 10 [m/s] (36 [km/h]) up to 100 [m/s] (360 [km/h]) increases the rail displacement and velocity in the range of 25% up to 37% also the rail acceleration in the range of 9% up to 14%. The velocity and acceleration of the sleeper also the ballast velocity increase in the range of 24% up to 30% and 7% up to 9%, respectively, by increasing the speed of the train from 10 [m/s] (36 [km/h]) to 100 [m/s] (360 [km/h]) in all three modes without applying axial force, considering compressive and tensile one in the train-track interaction system.

The Dynamic Train–Track Interaction on a Bridge and in a Tunnel Compared with the Simultaneous Vehicle, Track and Ground Vibration Measurements on a Surface Line

The vehicle–track interaction generates forces and consequently vibrations in the environment. The interaction has been analysed by the simultaneous measurements of vehicle, track and ground vibrations during test runs with varied train speeds. The special effects of the passage over a bridge and through a tunnel are studied and compared with the measurements on a conventional ballasted surface line. The maximum amplitudes, narrow band and one-third octave band spectra are presented for the axle-box accelerations and for the track, bridge and ground vibrations. The different frequencies and frequency bands are related to wheel out-of-roundness, track alignment errors, the sleeper passage and the wheelset–track resonance. An axle impulse component has been observed at the track, at the near-field soil and as a scattered version in the far field. Specific results can be found for the bridge track, where clearly speed-dependent bridge resonances occur due to the axle sequence of the train, and for the tunnel track where soft rail pads are responsible for a strong amplification around the wheelset–track resonance. On the other hand, the axle impulses are strongly reduced by the tunnel track, and the scattered axle impulse component is not as relevant as for the surface track. As a consequence, a strong mid-frequency amplitude reduction of the tunnel compared to the surface line has been measured for low and high train speeds by the Federal Institute of Material Research and Testing (BAM) and by other institutes.

Adaptive time series representation for out-of-round railway wheels fault diagnosis in wayside monitoring

Through the integration of advanced sensor technologies and machine learning algorithms, artificial intelligence has revolutionized wayside monitoring in the railway sector. Although several algorithms have been proposed for detecting out-of-roundness, i.e., flats, wear treads and polygonization, they generally fall short in isolating the root cause of the wheel's issue in a train passage. In this context, the paper presents a novel approach for wheel out-of-roundness diagnosis with (1) detection of aberrant train behavior; (2) isolation of specific defective wheels; (3) identification of the severity. For this, the methodology automatically segments a strain gauge signal, capturing the complex nature and temporal dependence of vibration patterns. This segmentation allows the extraction of localized accelerometer features in both the time and frequency domain, as well as implicit axle count and labelling of each wheel passage. Moreover, a single-value damage indicator based on anomaly detection algorithms was proposed. To validate the effectiveness of the proposed methodology, experiments on a set 3D numerical train-track dynamic interaction simulations are performed for different wheel profiles, track irregularities, train speeds, sensor placement and noise, associated to other environmental and operational variations. This demonstrates the potential of artificial intelligence for real-time assessment of wheels without interfering with normal service conditions, suggesting the possibility of automated fault diagnosis.© 2023 Elsevier Inc. All rights reserved.

Reconstruction of sleeper displacements from measured accelerations for model-based condition monitoring of railway crossing panels

Railway switches and crossings (S&C, turnouts) connect different track sections and create a railway network by allowing trains to change tracks. This functionality comes at a cost as the load-inducing rail discontinuities in the switch and crossing panels cause much larger degradation rates for S&C compared to regular plain line tracks. The high degradation rates make remote condition monitoring an interesting prospect for infrastructure managers to optimise maintenance and ensure safe operations. To this end, this paper addresses the development of tailored signal processing tools for condition monitoring using embedded accelerometers in crossing panels. Multibody simulations of the dynamic train–track interaction are used to aid the interpretation of the measured signals in a first step towards building a model-based condition monitoring system. An analysis is performed using sleeper acceleration measurement data generated by 100 000 train passages in eight crossing panels. Based on the given data, a novel frequency-domain displacement reconstruction method is developed and the robustness of the method with respect to encountered operational variability of the measured data is demonstrated. The separation of the track response into quasi-static and dynamic domains based on deformation wavelength regions is proposed as a promising strategy to observe the ballast condition and the crossing geometry condition, respectively.

Parameter optimization of a new cone-oriented elastic side-supporting long sleeper damping track: Experiment and simulation

Ground vibration and noise have been frequently observed in urban rail transit as a consequence of severe train-track dynamic interaction. To reduce train-induced vibration and noise, a new cone-oriented elastic side-supporting long sleeper damping track (COESSLSDT) is proposed in this paper. Unlike traditional sleeper damping tracks, COESSLSDT sleeper is suspended by two pairs of conical elastic side-supporting pads (ESSPs) on both sides, and the outer sides of ESSPs are connected with both sides of the sleeper groove by conical interference fit. Firstly, the mechanical performance of the COESSLSDT was obtained through static and dynamic analyses with a finite element (FE) model and then validated in the field. Then, the proposed model was used to evaluate the effects of key structural parameters of ESSPs on the mechanical performance and energy dissipation performance of COESSLSDT. Finally, the effect of side and bottom supports on the dynamic responses of the track structure under drop hammer impact load was studied, and the numerical results were compared with field test data. Both computational and experimental results demonstrate that COESSLSDT have good mechanical and dynamic responses control performance.

Optimisation of slab track design considering dynamic train–track interaction and environmental impact

Modern railway tracks for high-speed traffic are often built based on a slab track design. A major disadvantage of slab track compared to conventional ballasted track is that the environmental impact of the construction is higher due to the significant amount of concrete required. In this paper, the dimensions of the rectangular cross-sections and the types of concrete used in slab tracks are optimised with the objective to minimise greenhouse gas emissions, while considering the constraint that the design must pass the static dimensioning analysis described in the European standard 16432-2. The optimised track design is also analysed using a three-dimensional (3D) model of vertical dynamic vehicle–track interaction, where the rails are modelled as Rayleigh–Timoshenko beams and the concrete parts are represented by quadratic shell elements. Wheel–rail contact forces and the time-variant stress field of the concrete parts are calculated using a complex-valued modal superposition for the finite element model of the track. For the studied traffic scenario, it is concluded that the thickness of the panel can be reduced compared to the optimised design from the standard without the risk of crack initiation due to the dynamic vehicle load. In parallel, a model of reinforced concrete is developed to predict crack widths, the bending stiffness of a cracked panel section and to assess in which situations the amount of steel reinforcement can be reduced. To reduce the environmental impact even further, there is potential for an extended geometry optimisation by excluding much of the concrete between the rails.

Testing and Modelling of Elastomeric Element for an Embedded Rail System.

Modelling of elastomeric elements of railway components, able to represent stiffness and damping characteristics in a wide frequency range, is fundamental for simulating the train–track dynamic interaction, covering issues such as rail deflection as well as transmitted forces and higher frequency phenomena such as short pitch corrugation. In this paper, a modified non-linear Zener model is adopted to represent the dependences of stiffness and damping of the rail fastening, made of elastomeric material, of a reference Embedded Rail System (ERS) on the static preload and frequency of its deformation. In order to obtain a reliable model, a proper laboratory test set-up is built, considering sensitivity and frequency response issues. The equivalent stiffness and damping of the elastomeric element are experimentally characterised with force-controlled mono-harmonic tests at different frequencies and under various static preloads. The parameters of the non-linear Zener model are identified by the experimental equivalent stiffness and damping. The identified model correctly reproduces the frequency- and preload-dependent dynamic properties of the elastomeric material. The model is verified to be able to predict the dynamic behaviour of the elastomeric element through the comparison between the numerically simulated and the experimentally measured reaction force to a given deformation time history. Time domain simulations with the model of the reference ERS demonstrate that the modelled frequency- and preload-dependent stiffness and damping of the elastomeric material make a clear difference in the transient and steady-state response of the system when distant frequency contributions are involved.

Dynamic Behavior in Transition Zones and Long-Term Railway Track Performance

Transition zones between embankments and bridges or tunnels are examples of critical assets of the railway infrastructure. These locations often exhibit higher degradations rates, mostly due to the development of differential settlements, which amplify the dynamic train-track interaction, thus further accelerating the development of settlements and deteriorating track components and vehicles. Despite the technical and scientific interest in predicting the long-term behavior of transition zones, few studies have been able to develop a robust approach that could accurately simulate this complex structural response. To address this topic, this work presents a three-dimensional finite element (3D FEM) approach to simulate the long-term behavior of railway tracks at transition zones. The approach considers both plastic deformation of the ballast layer using a high-cycle strain accumulation model and the non-linearity of the dynamic vehicle-track interaction that results from the evolution of the deformed states of the track itself. The results shed some light into the behavior of transition zones and evidence the complex long-term response of this structures and its interdependency with the transient response of the train-track interaction. Aspects that are critical when assessing the performance of these systems are analyzed in detail, which might be of relevance for researchers and practitioners in the design, construction, and maintenance processes.

Analysis of buckling failure in continuously welded railway tracks

Continuously welded rails (CWR) are sensitive to thermal and train loads which could destabilize the track and cause buckling. The study of track buckling in the literature, however, is mostly focused on static analysis of CWR tracks under thermal loads. Yet in reality, train dynamic loads in lateral, vertical and longitudinal directions can have a major impact on track buckling behaviour. Moreover, track and wheel defects can aggravate the dynamic train track interaction loads, and reduce the safety against track buckling. The aim of this paper is to have an in-depth comparison of static and dynamic track buckling by employing a multi-body train-track dynamic model and a 3D finite element track model. Various scenarios are elaborated, base scenario dealing with static thermal analysis, dynamic analysis for a steady motion of a wagon with constant speed, dynamic analysis for a wagon with defect free wheels during braking, and dynamic analysis for a wagon with out of round defect wheels during braking. For each scenario, a sensitivity analysis of relevant parameters is also presented. Based on the results, it is concluded that train loads can significantly change the buckling temperature, as well as the safe temperature. For a severe braking of a wagon with out of round wheel defect of order 3, buckling temperature is almost 5.5 °C less than that of the static case. The drop for safe temperature in this case is 6.7 °C.

Long-term deformation of railway tracks considering train-track interaction and non-linear resilient behaviour of aggregates – a 3D FEM implementation

Railway track designers and maintenance entities have long been pursuing for a robust and reliable method to predict the track’s long-term behaviour. The complexity of this railway system, in terms of its changing structural and material behaviour throughout its life cycle, have hindered that quest. This paper presents a novel computer implementation focused on the estimation of the ballast and sub-ballast long-term deformation that provides a realistic reproduction of the actual behaviour of the structures because (i) it considers the three-dimensional aspect of the problem, (ii) incorporates accurate non-linear resilient material laws for the granular layers, (iii) uses a robust constitutive high-cycle strain accumulation model specifically devised for railway tracks that accounts for the three-dimensional stress conditions to determine both the volumetric and deviatoric permanent deformations and (iv) explicitly considers the dynamic train-track interaction. After calibration and validation with the results from an experimental case study comprising a physical model, a simulation scenario, considering different train types, is presented to demonstrate the potential of this approach. This implementation allows the construction of sufficiently extensive and elaborate representations of the railway track, allowing the study of geometrically complex cases and of the influence of many other aspects on its long-term behaviour.

Effect of Rail Pad Stiffness on Vehicle–Track Dynamic Interaction Excited by Rail Corrugation in Metro

Rail corrugation can cause intense dynamic interaction between train and track, which can reduce riding comfort and lifespan of track structure, and even threaten running safety. Instead of investigating the root cause and growth of corrugation, this case study aims to investigate possible solutions to the excess train–track dynamic interaction excited by rail corrugation in a metro track through both numerical analysis and field experiments. Numerical analysis was performed based on a vehicle–track coupled dynamical model with field-measured rail corrugation information from two curves. The numerical analysis results indicated that rail pad stiffness was the key factor affecting wheel–rail contact force in the studied direct fixation type transit track system. Rail pads with a lower stiffness could reduce the wheel–rail interaction; however, softer rail pads will also increase the rail displacement. Therefore, both the wheel–rail contact force and rail displacement need to be considered while determining the optimal rail pad stiffness. New rail pads with a stiffness of 35 MN/m, which are softer than the original rail pads with a stiffness of 50 MN/m, were recommended for the track in this study. Through field validation and long-term monitoring, new rail pads have been proven to effectively reduce the vehicle–track dynamic interaction and ease the development of rail corrugation to a certain extent. Compared with regular rail grinding, using rail pads with the appropriate stiffness can save transit agencies a tremendous amount of time and cost. The observations from this case study can benefit transit facing rail corrugation problems.

Dynamic Train–Track Interactions and Stress Distribution Patterns in Ballasted Track Layers

AbstractThis paper focuses on developing train–track dynamic interaction models by consideration of ballast and subballast layers’ stress distribution patterns. In this paper, the existing railway ...

Idealisations of Dynamic Modelling for Railway Ballast in Flood Conditions

As the main component of a ballasted railway system, railway ballast is frequently used by the railway industry to enhance constructability and practicality. Numerous studies into train–track interactions focused on ballast modelling and idealisation in completely dry environments, but recent studies have found that, in extreme weather such as floods, water can clog natural ballast beds and change the initial state of their properties. Ballast models used in multi-body simulations have been mostly developed based on the instrumented impact hammering method considering the ballast as a spring/dashpot. The single degree of freedom (SDOF) idealization for ballast enables a non-destructive field testing technique for monitoring of railway components in practice. In this study, the suitability of the idealization of ballast for dynamic characteristics has been evaluated. A series of experiments have been performed with a variety of ballast conditions in flooding levels from 0 to 40 cm, with a frequency range of 0–500 Hz. The results clearly show that the increase in the flood level will result in increasing dynamic damping of more than 50% of dry natural ballast whilst reducing its stiffness and natural frequency. The novel insights are of great significance for exploring the non-linear dynamic traits of ballast in extreme environments, which can be integrated into the coupled train–track analysis that can better express more realistically the dynamic train–track interaction and load transfer mechanism of flooded railway tracks.

A new strategy to estimate static loads for the dynamic weighing in motion of railway vehicles

The present paper focuses on the numerical modeling of a weigh-in-motion system developed with the purpose of assessing the static loads imposed by the train onto the track infrastructure. Weigh-in-motion systems would be useful in overcoming the disadvantages typical of the conventional static weighing such as costs and traffic management. However, contrary to the conventional static weighing, weigh-in-motion systems do not allow a direct measurement of the static load since the train–track dynamic interaction gives rise to dynamic loads that are added to the static ones. This study investigates how train speed and track unevenness affect the loads assessed by the weigh-in-motion system. In order to achieve that goal, a comprehensive statistical study was performed based on an extensive amount of calculations. Finally, based on the conclusions and trend identified through the comprehensive parametric study, an approach is proposed to correct the direct result given by the weigh-in-motion system in order to obtain an estimation of the static load.

Contributions of longitudinal track unevenness and track stiffness variation to railway induced vibration

Dynamic train-track interaction originates from excitation mechanisms such as longitudinal track unevenness, parametric excitation due to track stiffness variation and impact excitation due to wheel flats, wheel out-of-roundness and rail joints. Track stiffness variation can be regarded as longitudinal track unevenness in loaded condition, but for the mitigation of track geometry degradation it is important to distinguish between track unevenness in unloaded condition and track stiffness variation. This paper studies how longitudinal track unevenness and track stiffness variation contribute to railway induced vibration. A case study is performed for a railway line in Furet, Sweden. Based on measured track unevenness and stiffness data from the IMV 100 track recording car, the train-track interaction forces and free field vibrations are computed for each of these two excitation mechanisms separately, as well as for a combination of both. The computed free field vibrations are in good agreement with measured vibrations at the same site. The contribution of the track stiffness variation to the interaction forces and free field vibrations is much lower than the contribution of the longitudinal track unevenness. Track stiffness variation can also be modeled as equivalent track unevenness, leading to results slightly different from those obtained when track unevenness and track stiffness variation are modeled separately, and a poorer agreement with the measured vibrations.

Effects of Pier Deformation on Train Operations within High-Speed Railway Ballastless Track–Bridge Systems

The deformation of a bridge foundation (i.e. pier) for a ballastless track of a high-speed railway may cause additional irregularities within the track, thereby affecting train operation. By using a unit slab ballastless track bridge system as the research object, this study built a finite element model and a train–track dynamic interaction model. The additional rail deformation caused by the vertical or lateral deformation of a bridge pier was calculated by the finite element model, and then the effects on train operation due to the additional rail deformation were analyzed by the train–track dynamic model. It was found that the lateral deformation of a single pier should be of the most concern for the management and control of a high-speed railway. Specifically, when a pier suffered settlement and lateral deformation concurrently, the evaluation indices of train operation were primarily affected by the magnitude of the lateral deformation, and were only slightly affected by the settlement.

Short soil–binder columns in railway track reinforcement: three–dimensional numerical studies considering the train–track interaction

The authors present a numerical study on railway track subgrade reinforcement using short soil-binder columns through injection, below the ballast layer. A 3D FEM program developed in MATLAB that considers the dynamic train–track interaction and the non-linear elastic behaviour of the ballast is used to study the response of the train–track–substructure system and assess stresses in the subgrade. Results suggest that reinforcements have limited impact on the train–track interaction and reduce deviatoric stresses between columns, at the top of the foundation. This method may be particularly relevant in the rehabilitation of old single railway tracks.

Rolling Contact Fatigue on premium rail grades: Damage function development from field data

The concept of the rail damage function provides vital understanding of the operational performance of rail grades in terms of surface degradation. The present study extends this concept from conventional to premium pearlitic rail. This is done on the basis of both simulations of dynamic train-track interaction and field observations. Rolling Contact Fatigue (RCF) damage index values for the conventional R260Mn and the premium R370CrHT grade rail are established, describing the behaviour of the associated damage functions. Defining the individual rail grade damage response to operational loading levels, the potential of the RCF-damage function to support the process of rail grade selection and track maintenance is further discussed.

Numerical investigation of the effects of unsupported railway sleepers on train-induced environmental vibrations

Review of technical literature regarding to train-induced vibrations shows that the effects of unsupported railway sleepers on this issue have been less investigated. So, the present study was devoted to numerical investigations of the mentioned issue. In this regard, first the problem of longitudinal train–track dynamic interaction was simulated in two dimensions by using the finite element method and the developed model was validated through comparison of the results with those obtained by previous researchers. In the next stage, a series of sensitivity analyses were accomplished to account for the effects of value of gap beneath the unsupported sleeper(s) and the track support stiffness on increasing the sleeper displacement and track support force. Moreover, the raised sleeper support force was introduced as applied load to a two-dimensional plane strain finite element model of track in lateral section and consequently the train-induced vibrations were assessed. As a result, a series of regression equations were established between the peak particle velocity in the surrounding environment of railway track and the sleeper support stiffness for tracks without unsupported sleepers and with one and two unsupported sleepers.