Rail Deformation Research Articles

A Non‐Iterative Wheel‐Rail Contact Geometry Determination Algorithm and Its Application

AbstractTo ensure a more accurate simulation of the wheel‐rail contact state in vehicle‐track interaction, a non‐iterative contact geometry determination algorithm is proposed. This algorithm decouples lateral movement and roll, independently calculates the minimum wheel‐rail gap on both sides, and overcomes the limitation of simultaneous wheel‐rail contact on both sides. It can be applied to single‐side and two‐side wheel‐rail separation problems. Additionally, by converting track irregularity and rail deformation into the reverse displacement of the wheel, it avoids real‐time calculation of the wheel‐rail spatial position, thereby improving calculation efficiency. The effectiveness of the algorithm is verified through Universal Mechanism software and field measurements. Subsequently, the influence of the measured wheel‐rail profile, rail cant, and rail gauge on the wheel‐rail contact characteristics is analyzed. Finally, vehicle shaking caused by track irregularity and wheel‐rail contact is examined from the perspective of wheel‐rail matching. The study demonstrates that the non‐iterative algorithm is suitable for online simulation by pre‐processing the contact geometry parameters. When the track gauge and rail cant increase, the distribution of wheel‐rail contact points becomes more concentrated. Furthermore, when the excitation frequency of wheel‐rail matching is close to the track irregularity excitation frequency, it causes vibration amplification, resulting in lateral vehicle shaking.

Riding safety prediction of a high-speed train running on transition zone under foundation settlement

The settlement of piers and subgrade bending deformation are widely recognized as common issues in the transition zones of high-speed railway bridges. This study aims to investigate the settlement behavior within these transition zones and its impact on the dynamic interaction between trains and the track. To achieve this, a vehicle-track-transition zone mapping relationship model is developed to analyze both the settlement behavior and the resulting dynamic response characteristics. The study employs the finite element method and multi-body dynamics to construct the simulation model. Settlement effects are simulated using the Newton-Raphson iterative method, with the additional rail deformation caused by foundation settlement serving as the excitation for the vehicle-track-transition zone dynamic interaction system. In the numerical analysis, the dynamic effects of three key factors—train speed, transition zone length, and the amplitude of foundation settlement—are examined based on the performance of the vehicle-track-transition zone interaction. The time-frequency technique is utilized to comprehensively reveal and clarify the spatial-frequency characteristics of system responses influenced by settlement excitation. Moreover, the relationship between the safety-based settlement threshold and these three factors is calibrated.

Analytical study on geometrical irregularity and internal loads of railways with CRTS I ballastless tracks on arch bridges subject to thermal effects

Temperature variation causes geometrical irregularity and additional internal loads in railway systems. The geometrical irregularity and additional internal loads can adversely influence the dynamic behaviors of trains, therefore compromising the safety and ride comfort of trains. This paper presents an analytical study on the deformations and internal loads of railways with CRTS I ballastless tracks on an arch bridge. The bridge is located in the Sichuan-Tibet Railway Line within a high-altitude mountainous terrain exposed to significant temperature variations. This research derives analytical formulae to analyze the deformations and internal loads of railways under various temperatures and thermal gradients. The formulae are utilized to evaluate the effects of the stiffness of fasteners and the stiffness of isolation layers of CRTS I ballastless tracks. The results show that temperature changes cause significant vertical deformations and rotations of rails, and reducing the stiffness of fasteners and isolation layers is effective in mitigating rail deformations under the thermal effects.

Dynamic mechanical behaviors of pearlitic U71MnG rail steel: Deformation mechanisms and constitutive model

Pearlitic rail steels with excellent mechanical and wear properties are widely employed for high-speed railways. During the service period, the presence of track irregularities, switches, as well as crossings can cause intense dynamic loadings, which accumulate the severe deformation of rails, and sometimes even facilitate crack initiation and failure. Knowledge of the dynamic mechanical response and damage behaviors of the rail steels is therefore important for the service performance estimation of railways. In this study, the pearlite U71MnG rail steel was deformed using a split Hopkinson pressure bar (SHPB) apparatus to reach a wide range of strain rates and temperatures. Microstructures including the grain morphology, deformation characteristic of cementite lamellae, dislocation substructures in ferrite lamellae, and phase transformation at pearlite colony boundaries were characterized. Based on the microstructural observations, the rate-controlling strengthening mechanism and temperature-dependent softening mechanism of the steel were revealed when the process for the dynamic loading-induced cementite decomposition at boundaries was discussed. In consideration of the athermal deformation mechanism, thermally activated mechanism, and viscous-drag effect, a physically based constitutive model was proposed to describe the dynamic mechanical response of the pearlite rail steel. The predicted flow stresses were found to be consistent with the experimental one for all strain rates and temperatures.

Development of a new design methodology for slab track systems

Owing to the rapid increase in the demands of train speed and axle loads, the slab track has been introduced to replace the ballast in the classical ballasted track with reinforced concrete slab or asphalt-bearing layer to improve the track stability, strength, and durability. This paper aims to develop a new methodology for estimating the rail deformations for the most common slab track systems (BÖGL, Shinkansen, and RHEDA 2000. This methodology yielded the first design aid for slab track systems based on design equations and graphs for high-speed systems. Using a regression analysis of more than 300 finite element models which are validated by experimental tests, the relationship between the rail deflection, modulus of elasticity for subgrade and replacement, and the replacement thickness was determined for the most common slab tracks under the American (AREMA) and European (EN) loads. According to EN, it was found that the minimum modulus of elasticity for subgrade to fulfill the rail deflection criterion without a replacement soil ranges from 128 to 143 MPa for the most common slab track systems; meanwhile, for AREMA, it ranges from 59 to 70 MPa. Furthermore, for these slab track systems, one simple design chart was introduced to aid engineers with the design of the slab track replacement layer according to each design code.

A Method for Measuring the Mass of a Railroad Car Using an Artificial Neural Network

The fast, convenient, and accurate determination of railroad cars’ load mass is critical to ensure safety and allow asset counting in railway infrastructure. In this paper, we propose a method for modeling the mechanical deformations that occur in the rail web under the influence of a static load transmitted through a railway wheel. According to the proposed method, a railroad car’s weight can be determined from the rail deformation values. A solid model of a track section, including a railroad tie, rail, and wheel, is developed, and a multi-physics simulation technique that allows for the determination of the values of deformations and mechanical stresses in the strain gauge installation areas is presented. The influence of the loaded mass, the temperature of the rail, and the wheel position relative to the strain gauge location is considered. We also consider the possibility of using artificial neural networks to determine railroad cars’ weight without specifying the coordinates of the wheel position. The effect of noise in the data on the accuracy of determining the railroad car weight is considered.

Mapping the relationship between the temperature gradient of CRTS Ⅲ slab track on bridge and rail deformation in high-speed railways

Temperature gradient is an important factor affecting the periodic rail deformation of CRTS Ⅲ and the running stability of high-speed trains. The Comprehensive Empirical Mode Decomposition with Adaptive Noise (CEEMDAN) method is employed for the analysis of test data in site from CRTS III slab tracks on high-speed railway bridges. The correctness of the coupling model has been validated through data on-site. To analyze the mapping relationship between the temperature gradient of the CRTS Ⅲ slab track on the bridge and rail deformation in high-speed railways, a rail-slab track-bridge thermal coupling model was established, and the rail deformation distribution characteristics of the slab track on the bridge under the complex temperature gradient load were calculated. Furthermore, a prediction model of rail deformation under the action of the complex temperature gradient was proposed. The study results showed that the intrinsic mode function (IMF) decomposed by the CEEMDAN method reflects the sensitive wavelength of track irregularity and quantitatively describes the corresponding relationship between amplitude and seasonal temperature. In the measured data, the maximum amplitude of rail deformation caused by temperature differences in different seasons was 1.99 mm, reflecting the significant impact of temperature gradient on the additional track irregularities on the bridge. Under the action of the temperature gradient, the rail deformation of CRTS Ⅲ slab track on the bridge is the superposition of periodic sinusoidal fluctuation of the track and parabolic fluctuation of the simply supported beam. This study could provide a new method for predicting rail deformation and controlling track smoothness, so as to improve the stability and operation efficiency of trains.

Study on the long-distance settlement threshold of high-speed railway subgrade based on vehicle responses

The long-distance and large-scale subgrade settlement is a key issue in high-speed railway (HSR). This work focuses on the long-distance settlement threshold for the HSR subgrade. A Green’s function-based hybrid dynamic model with high efficiency is established to achieve the long-distance analysis of the vehicle-track-subgrade interaction system with a wide range of subgrade settlement. Based on the analysis results, the Wavelet decomposition technique is applied to extract the low-frequency components of vehicle responses excited by the additional deformation of rails induced by the long-distance subgrade settlement. The simulation results show that the low-frequency vibrations of vehicle are mainly excited by the additional deformation of rails induced by settlement. Based on the correlation between the vehicle responses and the second derivative of additional deformation of rails, the threshold of long-distance settlement can be determined. The vehicle response and subgrade settlement signal are linked in the time-frequency domain, and the relationship between system excitation and response is clearly revealed. This paper provides a referenceable analysis framework that is convenient for engineers in the control for the amplitude of large-scale subgrade settlement in HSR.

Large highway tunnels under operating metro lines in the soils of Santiago – Design and Control approach

AbstractThe Américo Vespucio Oriente II Concession (AVOII), part of the Urban Transport System of the Metropolitan Region of Santiago, Chile, includes the closure of the 65 km Américo Vespucio Ring in highway standard. The project involves the construction of two mostly parallel urban soil tunnels 5.2 km in length and three lanes in each direction and it will run below the existing Américo Vespucio Avenue. At the same time, it goes below the underground Metro Line 4 currently in operation. Skava Consulting SpA was hired by Metro as an expert reviewer of underground and surface works. The objective is to ensure that the existing Metro structures will not be affected by the construction or the operation of AVOII. The work involved highly complex 3D models. In search of a more efficient way to review the design, it was agreed to do finite difference models in the critical areas of the project. A total of 32 proper models were created. All of them proved to be useful in validating and correcting findings or deviations in the original design. Considering the above, and that the project runs at depths of 40 m in average – which for Santiago soil is uncommonly deep – it faces the challenge of an extremely low tolerance for disturbances in the surrounding ground. For this reason, specific subway rail deformation criteria must be fulfilled, and the surface and subsurface deformations must be monitored very frequently during the construction of the tunnel, due to commence in 3Q 2023.

Real-time temperature field and thermal deformation of slab track on cable-stayed bridge

This study aimed to master the real-time temperature fields of slab tracks on cable-stayed bridges and analyze the thermal deformations. The pivotal heat conduction parameters of the geotextile and rubber pad were obtained through testing, and the governing equations for heat conduction considering temperature variations were improved. A thermal-fluid-solid coupling model for slab track on cable-stayed bridge was proposed. The results indicated that the high temperatures of the track were concentrated within 0.05 m depth of the slab. Under the resistance of the isolation layer, the temperature on both sides of the geotextile isolation layer appeared obvious abrupt change. The time of maximum and minimum temperatures of the truss beam were the same as those of the air. The effects of real-time temperature change on the irregularity of the rail were obvious. In summer, the maximum vertical rail deformation was 201.88 mm and the transverse deformation was 17.87 mm. The temperature change in just one day caused vertical deformation of rail with a range of more than 60%. On a single day in summer, the maximum horizontal irregularity was 1.74 mm, which was less than the 2.0 mm specified in the code.

Evolutionary power spectral density study of the earthquake-induced dynamic irregularity based on short-time Fourier transform

The stiffness degradation of the track-bridge system under earthquake is the main reason for the deterioration of track dynamic smoothness. In order to investigate the dynamic smoothness performance of the track surface of the track-bridge system after earthquake. In this paper, a nonlinear time analysis of ballastless track-simply supported bridge system under transverse random earthquakes is carried out, and the degradation mode and degradation degree of each key component of the track-bridge system after transverse earthquakes are investigated. Based on the post-earthquake stiffness of each component, a train-track-bridge system considering earthquake-induced stiffness degradation is established. The sample library of earthquake-induced dynamic irregularity is constructed by additional deformation of rails, and the power spectral density of the earthquake-induced dynamic irregularity is studied. Based on the short-time Fourier transform irregularity inversion technique, the earthquake-induced dynamic irregularity characteristic curve based on the probability guarantee rate is proposed, and the effects of train operating speed and ground vibration intensity on the earthquake-induced dynamic irregularity characteristic curve are investigated. The research results show that: The transverse stiffness degradation of the bearings and piers of the track-bridge system is the most obvious during an earthquake, and the stiffness degradation degree of the middle piers is greater than that of the side piers. The stiffness degradation degree of the track-bridge system rises significantly with increasing PGA, while the variability of stiffness degradation of the middle and side piers drops. The most significant earthquake-induced dynamic irregularity sample is the track alignment irregularity. Low-frequency components dominate the evolutionary power spectral density corresponding to track dynamic irregularity, and the amplitude of the power spectral density reduces considerably with increasing spatial frequency. The vehicle speed has little effect on the earthquake-induced track dynamic irregularity. The irregularity amplitude grows significantly with increasing damage degree. The results indicated that the stiffness degradation damage degree of the track-bridge system under earthquake can be quantified by constructive earthquake-induced track dynamic irregularity.

Study on the optimization of high-speed turnout crossing structures based on actual elastic deformation of point and splice rails

In this paper, to address the shortcomings of the crossing structure design based on the elastic bending center method and the lack of related research, an optimization method for high-speed turnout crossing structures was proposed based on the actual elastic deformations of point and splice rails. Based on the finite element theory, the actual loading characteristics and spatial variable section characteristics of point and splice rails were fully considered, and a refined simulation analysis model of the switching system of point and splice rails in crossing areas was established. Moreover, the elastic deformation lines of point and splice rails in the nonworking state were obtained for the first time, which were consistent with actual situations. On this basis, system optimization was performed for the connecting parts of the crossing with a movable point in a high-speed turnout. In the crossing structure simulation model, the length adjustment values of the first–sixth spacer blocks between the branch line–wing and point rails and between the mail line–wing splice rails were ≤1 mm. Moreover, the lengths of the seventh–ninth spacer blocks decreased by gradually increasing amounts, and the length of the ninth spacer block decreased the most (∼6 mm). The length of the second spacer block between the point and splice rails slightly increased, but the length of the third spacer block significantly decreased by 6 mm. The length adjustment value of the distance block between the point and splice rails was smallest (0.7 mm). The calculated optimal lengths of the connecting parts of the crossing were found to be close to the empirical values used in actual manufacturing processes, and the dimension optimization patterns were completely consistent with actual situation, which validates the proposed optimization method. Thus, the proposed method can effectively improve the coordination between rails and connecting parts in crossing areas, substantially reduce internal stresses in crossing systems, and improve their assembly performance and service life. Moreover, the proposed optimization parameters can provide valuable references for the research on next-generation high-speed turnouts (400 km/h) and for improving the designs of existing high-speed turnouts.

Experimental and Numerical Visualisation of Subsurface Rail Deformation in a Full-Scale Wheel–Rail Test Rig

To tackle the problem of various types of rail damage, such as rolling contact fatigue (RCF) or wear, a profound knowledge of the occurring mechanisms is necessary. This paper presents a newly developed full-scale test rig experiment that involves inserting softer pins into the rail head. These tests help deepen our understanding of shear deformation in rail steels. Furthermore, a finite element (FE) simulation approach is introduced that can be related to the test rig experiments. With these experiments, in combination with the FE simulation, valuable information regarding the plastic deformation can be obtained. This methodology allows predictions regarding a rail’s material behaviour during cyclic wheel loading. Moreover, it enables an effective and rapid qualitative material assessment, reducing the costs of expensive and time-consuming experiments.

Research of deformation law about guide rails under the action of mining deformation in mine vertical shaft

To lay a foundation for alleviating the influence of mining shaft deformation (MSD) on the guide rail (GR) and monitoring the shaft deformation state, this paper studies the deformation law and mechanism of the guide rail under the MSD. Firstly, a spring is used to simplify the interaction between the shaft lining and surrounding rock soil mass (SRSM) under MSD, and its stiffness coefficient is deduced by the elastic subgrade reaction method. Secondly, a simplified finite element model is established based on spring element, the stiffness coefficient is calculated by the derivation formula, and its effectiveness is verified. Finally, the deformation law and mechanism of GR are analyzed under different types and degrees of MSD, and the deformation characteristics are studied under the disconnection between the shaft, bunton and guide rail. The results show that the established finite element model can better simulate the interaction between the shaft lining and SRSM, and the calculation efficiency is greatly improved. The guide rail deformation (GRD) has a strong ability to characterize MSD and owns the distinctive feature corresponding to different types and degrees of MSD and the connection state. This research can provide reference and guidance for the shaft deformation monitoring and the maintenance and installation of the GR, and also lays a groundwork for studying operation characteristic of hoisting conveyance under MSD.

Running safety of high-speed railway vehicles on the elastoplastic track-subgrade-bridge system under near-fault pulse-type earthquakes

In this study, the running safety assessment (RSA) of high-speed railways is carried out, with the wheel lift being the derailment criterion. Seventy near-fault pulse-type earthquakes (NFPTEs) are imposed on an elastoplastic vehicle-track-bridge coupled model with elastoplastic supports and shear keys. Since the bridge length in the simulation model is limited by the 14-span high-speed railway simply supported bridge prototype with subgrades and a CRTS II track plate, it is difficult for the vehicles going through the full time-history of ground motions while passing over the bridge. Therefore, the excitation-input-time (EIT) analysis is conducted herein, and it is found that the effects of EIT on RSA under NFPTEs are significant and, as such, cannot be ignored. The EIT analysis also shows that the appearance times and EITs of peak ground acceleration and peak ground velocity of NFPTEs significantly affect the RSA results. In order to reveal and describe the potential relationship between dynamic responses of rail and wheel lift, dynamic contact point responses (DCPRs) are also proposed, and after comparison with the traditional dynamic responses, including rail deformations and displacements, the dynamic contact point velocity in Y-direction (DCPV-Y) are selected for developing of relationship with wheel lift and RSA limitation zone proposal.

Effect of girder deformation on the dynamic performance of high-speed train-track-bridge coupling system

Aiming at the high-speed railway (HSR)-China Railway Track System III (CRTS III) slab ballastless track (SBT)-simply-supported bridge system, the mapping relationship between girder deformation and rail deformation had been deduced theoretically, and then, the additional irregularity of the rail was obtained. A dynamic model of the high-speed train-track-bridge (TTB) coupling system was established according to existing theory on the high-speed TTB dynamic interactions. Combined with the mapping relationship, taking the superposition of the additional irregularity and the random irregularity as excitation, the dynamic response of two train models (CRH2 and ICE3 trains) was analysed by using the high-speed TTB coupling system model. The recommended thresholds of girder deformation were given based on running safety and ride comfort indicators. The results show that the sensitivities of the two train models exposed to girder deformation were different, and the CRH2 train was more sensitive to the lateral girder deformation. The non-uniform dislocation deformation of multiple girders exerted a slightly more significant effect on the dynamic characteristics of two train models than the dislocation deformation of single girder. Under the same amplitude of girder deformation, the influences of vertical girder dislocation and vertical girder rotation on the running safety and ride comfort of trains were significantly greater than that of lateral girder dislocation and lateral girder rotation. Acceleration and wheel-rail force increase rapidly in the area of girder deformation. To guarantee running safety and ride comfort of trains, this paper proposes suggested values for girder deformation thresholds.

Tunneling construction technology of shafts and cross-passages under strictly controlling deformation of the existing railway

Underground construction will have more or less adverse effects on adjacent existing buildings with more and more existing buildings above ground. However, this situation has only been reported by a small number of researchers. In view of this, this article takes the existing airport line shaft and horizontal passage project in the western suburb of Beijing Metro Line 12 as the background to study the impact of the construction of subway station and shaft passage on the adjacent existing railway. Based on the above project reality, under the action of pavement load, the effects of different parameters (the distance between the surface measuring point and the middle line of the transverse passage and the substep of construction loading sup step) on the surface settlement and track deformation of the shaft and cross-passage through the existing railway are studied by numerical analysis method. The calculation results show that the construction method of shaft and cross passage is reasonable. The comprehensive reinforcement measures of subgrade, rail and hole are effective, effectively controlling the deformation of subgrade and rail within the standard value (surface settlement ≤60 mm, rail deformation ≤6 mm). In addition, the numerical simulation data can better represent the actual situation as a whole.

Passenger ride comfort in subway due to new subway excavation below

New tunnel excavation below existing tunnel deforms the rails inside the existing tunnel. The settlement-induced rail irregularity intensifies the wheel-rail interaction, which reduces passenger ride comfort of the existing tunnel. This research investigates the passenger ride comfort of the existing tunnel due to new tunnel excavation. A project of new twin tunnels excavation below existing triple tunnels is introduced. According to the field monitoring data, the settlement of each of the existing tunnels, although supported by different types of lining, can be fitted by the Gaussian function. Then numerical simulation is performed to study the deformation characteristics of the existing rails, which is difficult to monitor in the field. The simulation results show that the tunnel deformation can well represent the rail deformation. After that, train ride comfort is adopted to evaluate passenger comfort indirectly. The vehicle dynamic performance due to settlement-induced track irregularity is studied by a general multibody system simulation software. The results show that the vertical acceleration of the car body increases linearly with the increase of the settlement amplitude and decreases exponentially with the increase of the trough width i. When the trough width i is larger than 15 m, the vertical accelerations produced by new tunnel excavation are negligible compared to those produced by track irregularity. The settlement amplitude limits considering the passenger ride comfort in subway due to new subway excavation below are obtained.

Advanced Representative Rail Temperature Measurement Point Considering Rail Deformation by Meteorological Conditions and Rail Orientation

Advanced Representative Rail Temperature Measurement Point Considering Rail Deformation by Meteorological Conditions and Rail Orientation

An Analytical Solution for the Geometry of High-Speed Railway CRTS Ⅲ Slab Ballastless Track

To study the mapping relationship between girder deformation and rail deformation for the CRTS Ⅲ slab ballastless track (SBT) multi-span simply supported bridge, this study derived a simplified analytical solution, and the corresponding ANSYS finite element model (AFEM) was established. Compared with the fine analytical model (FAM) and the AFEM, the calculation results of the three models under the conditions of pier settlement and girder vertical fault were compared, which verified the universal properties of the simplified analytical model (SAM). Based on the verified SAM, the influence of pier settlement, fastener stiffness, girder span, and girder vertical fault on rail deformation was studied. The results show that the rail deformation is approximately proportional to pier settlement and girder vertical fault. With the increase in fastener stiffness, the fastener internal force increases, the rail mapping deformation increases, and the length of the rail mapping deformation area decreases. With the increase in girder span, the rail deformation curve becomes smooth, the length of the rail mapping deformation area becomes longer, and the fastener internal force is significantly reduced.