Ballastless Track Research Articles

Quasi-distributed optical fiber sensing for the coupled vibration analysis of high-speed train-bridge coupled system under earthquakes

Due to the extensive construction of high-speed rail lines passing through seismically active areas, the possibility of a sudden earthquake occurring during train operation is very high. Additionally, the earthquake will intensify the dynamic response of trains and bridges, causing serious bridge damage. In this work, the dynamic response behavior of the bridge structures in the coupled train-bridge system under the earthquake is investigated based on the 4-table shaking table system. Shaking table experiments are also conducted on a high-speed railroad model of simple-supported girder bridge at a scale of 1/10 with the simulated layers of China Railway Track System type II (CRTS II) ballastless track slabs. The strain responses of various components, including rails, track plates, base plates, and beams, were measured on the bridge using quasi-distributed fiber optic gratings, both with and without seismic actions. Additionally, the seismic isolation characteristics of the fasteners and the CA mortar layer were investigated. The dynamic performance of the coupled train-bridge system under earthquakes was studied in both the time and frequency domains.

The stochastic characteristics of wideband-wavelength track irregularity on Chinese HSRs and its application to dynamic wheel–rail interaction

Track irregularities are the major excitations which lead to unfavourable wheel–rail dynamic interaction. In this work, the stochastic characteristics of longitudinal level irregularity on Chinese ballastless high-speed railway (HSR) are analysed based on a series of large-scale measurement campaigns on various arterial lines in Chinese HSR network. The power spectrum density (PSD) of longitudinal level irregularities of various track types is obtained, covering short and middle-to-long wavelength range, as well as the periodical irregularities caused by characteristic lengths of track components. An irregularity spectrum is proposed to represent the stochastic characteristics of the longitudinal level irregularities. Unlike existing irregularity spectra which represent the short and middle-to-long wavelength irregularities separately, the proposed spectrum covers a wide range of wavelength from 0.002 m to 100 m. A vehicle–track model which couples flexible wheelsets and the ballastless track is employed to demonstrate the suitability of the spectrum. It is shown that the proposed spectrum is more suitable than the latter to represent Vehicle–Track Interaction (VTI) on Chinese HSRs. The fitted short-wave spectrum and the proposed wideband wavelength spectrum therefore provide more appropriate representatives of track irregularities for accurate modelling of VTI on Chinese HSRs and railway lines which adopt similar technologies.

Experimental Study on Compression Failure of Type II Ballastless Track Slab Based on Optical Fiber Sensing

Ballastless track structures are widely employed in high-speed rail networks because of their superior safety and durability. Among the various types of ballastless track, the Type II slab is currently one of the most extensively used and mature technologies in practice. Over the course of its service life, the damage within the ballastless track structure gradually accumulates in response to increased external loads. Therefore, it is crucial to continuously monitor the health condition of the track structure. In this study, a quasi-distributed fiber optic sensing system is adopted to monitor the deformation capacity and force performance of a Type II ballastless track slab under vertical load. The investigation aims to analyze the damage mechanism of the track structure under vertical pressure by assessing the deformation differences among its different components. The findings reveal that the incorporation of vertical reinforcement can enhance the pressure bearing capacity of the cement asphalt mortar layer to a certain extent, subsequently affecting the stress dilation. The stress performance of the ballastless track slab can be effectively monitored using the quasi-distributed fiber optic sensing technology under pressure. The outcomes of this research offer valuable insights for controlling displacement and analyzing damage in ballastless railway systems subjected to compression.

Mechanical behaviors of ballastless track under temperature and vehicle loads in high geo-temperature tunnel

To explore the temperature field, temperature effect and mechanical behaviors of the track structure under combined load in high geo-temperature tunnel, the temperature field test platform is built to simulate the conditions under which the track bottom is heated in high geo-temperature tunnel, and the temperature distribution of the track bed slab in the transverse, longitudinal, and vertical directions is investigated. Then, the numerical model is built to examine the displacement and stress of the track structure under temperature load and combined load consisting of temperature and static vehicle load. The results show that when the temperature load on the track bottom is 30 ℃, the vertical temperature gradient inside the slab is negative, with a maximum of 20 ℃/m, and the maximum temperature differences in the vertical, transverse, and longitudinal directions are 5 ℃, 3.25 ℃ and 2 ℃, respectively. The temperature deformation of the track bed slab is manifested as sinking in the middle and warping at the edge, with the maximum tensile stress occurring in the upper-middle region and the maximum compressive stress in the lower-middle region. Under the combined load, the most unfavorable position of the vehicle load is where the front wheel is in the center of the slab, and for every 5 tons increase in axle load, the maximum tensile stress of the slab increases by about 4%, and the maximum compressive stress increases by about 2%. The findings provide reference for the optimization design of track in high geo-temperature tunnel.

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.

Improvement of impact acoustic inspection for high-speed railway track slabs using time–frequency analysis and non-defective machine learning

Slab track is one of the most highly used ballastless track forms in Japan's high-speed railway system (Shinkansen) and is composed from track slabs (precast RC or PRC member), a filling layer (mixture of cement, asphalt emulsion and fine aggregates) and concrete bed. As they age, it has been reported that the supporting conditions of track slabs change due to damage in the filling layer that in turn affects running stability. It is necessary to evaluate supporting conditions of track slabs accurately during maintenance of slab tracks prior to signs of cracking. Some previous works show the usefulness of impact acoustics and non-defective machine learning using frequency response spectrums as feature values for evaluating supporting conditions of track slabs. In this study, we examine a method of non-defective learning to improve the evaluation of supporting conditions: time-frequency response characteristics of impact acoustics using time-frequency analysis and resulting spectrograms as feature values. As a result, we have improved accuracy rate (from 81.90 % to 86.72 %) and F-value (from 70.79 % to 78.75 %) more precisely than conventional method based on frequency response functions as feature values.

Mechanical properties and damage evolution features in uniaxial compression with non-coincident interlayer contact in double-block ballastless track

As interlayer cracking has become as a significant issue in ballastless tracks, investigating the mechanical properties and damage characteristics during uniaxial compression with non-coincident contact is vital for enhancing the operational performance of ballastless tracks. This study conducted experiments on interlayer non-coincident contact damage in double-block ballastless tracks with nominal normal pressures of 0.666 MPa, 1.244 MPa, 2.489 MPa, and 3.733 MPa. The research explored the relationship between normal load and normal deformation stiffness, analyzed the interlayer contact damage mechanism of concrete, and investigated the damage evolution mechanism under non-coincident contact conditions based on Acoustic Emission (AE) signals. The findings indicate that: I) When the nominal pressure is respectively less than and greater than 1.333 MPa, the normal deformation stiffness and normal load satisfy linear and power function relationships, respectively. II) The interaction of interlayer protrusions under non-coincident contact, combined with the outward expansion resulting from interlayer mutual compression deformation, are two significant factors contributing to the formation of tensile cracks, while the presence of significant shear stresses directly beneath the interlayer contact points is the primary cause of shear cracks. III) After loading, The ballastless track slab matrix remains undamaged, while the supporting layer matrix may experience comprehensive cracking when the nominal pressure exceeds 1.333 MPa. IV) During the stage of only interlayer interface damage, both tensile and shear cracks are the primary causes of concrete damage. In the stage where damage occurs to both the interlayer interface and matrix, tensile cracks play a dominant role. However, when comprehensive matrix cracking occurs, shear cracks take on a dominant role. The outcomes of this study contribute to a deeper understanding of the damage mechanisms of ballastless tracks under train loads following interlayer cracking. Particularly focusing on the evolution characteristics of damage under high interlayer pressure.

The Influence of CRTS II Slab Ballastless Track Upper Arch Deformation on the Wheel Jumping Law of High-Speed Vehicle

To study the impact of upwarp deformation in the ballastless track on the jumping behavior of the high-speed vehicle, utilizing UM and ANSYS joint simulation, a vertical vibration model of high-speed vehicle on CRTS II slab ballastless track was developed based on the non-Hertz wheel–rail contact model of virtual penetration theory. By using the single-wave cosine curve simulating the characteristics of upwarp deformation in the track slab, we calculated the whole process of wheel jumping. This allowed us to analyze how the amplitude and wavelength of the track slab upward deformation influence the vibration response of the vehicle–track system. Our findings indicate that when a wheel passes through the arch section of the track slab, the entire wheel jumping process consists of distinct stages: “wheel–rail bonding, wheel–rail separation, wheel–rail impact (one or more times), and wheel–rail bonding.” As the amplitude of upwarp deformation increases and the wavelength decreases, significant changes occur in several parameters, including the vertical force between the wheel and rail, wheel unloading rate, wheel jump height, frequency, duration, and vertical displacement of the rail. Additionally, when the wavelength is between 2 and 6[Formula: see text]m and the amplitude is 8[Formula: see text]mm, the vertical force between the wheel and rail becomes zero, the wheel load reduction rate is one, and the wheel jumps. When the wavelength is less than 3[Formula: see text]m, the wheel jump height exceeds the flange height, increasing the risk of derailment. Meanwhile, during the first wheel–rail impact, the wheel–rail vertical force and the rail vertical displacement reach their maximum, potentially impacting rail service performance negatively. Finally, compared to the amplitude of the track slab camber deformation, its wavelength has a greater impact on the entire process of wheel jumping. It is recommended that attention be paid to the change in the wavelength of the track slab camber during the maintenance and repair of the ballastless track.

Quantification and visualization of vibration power flow in train-track-bridge coupled system under thermal effects

This paper presents an approach to investigate the effect of temperature on the transmission and distribution of vibration energy for train-track-bridge coupled systems. The vibration of the coupled system can be simulated by integrating the multi-body dynamics model of the train with the finite element models of the track and bridge. The transmission and distribution of vibration energy can be evaluated using a structural intensity method. This approach was implemented to investigate the vibration characteristics of a coupled system under extreme temperature conditions. The system consisted of a CRH2 high-speed train, a CRTS I double-block ballastless track, and an arch bridge. The results show that extreme temperature not only impacts the characteristics of vibration energy transmission in the coupled system but also affects vibration energy distribution. This research provides new insights into vibration control and optimization design for bridges in regions with significant temperature variations.

Damage Evolution of Ballastless Track Concrete Exposed to Flexural Fatigue Loads: The Application of Ultrasonic Pulse Velocity, Impact-echo and Surface Electrical Resistance Method

Damage Evolution of Ballastless Track Concrete Exposed to Flexural Fatigue Loads: The Application of Ultrasonic Pulse Velocity, Impact-echo and Surface Electrical Resistance Method

On the deformation of CRTS-Ⅲ ballastless track during the casting process of self-compacting concrete: Numerical simulations and random forest-based prediction models

CRTS (China railway track system)-Ⅲ slab track is a main structural type of ballastless track in Chinse high-speed railway (HSR), which requires precise positioning of prefabricated concrete track slabs. However, the cast-in-place process of the self-compacting concrete (SCC) filling layer induces a large deformation as the flowing SCC generates an up-lift force on the bottom of the track slab. Currently, the deformation mechanism and influencing factors of the track slab during the SCC casting process have not been thoroughly studied. In this work, a fluid-solid interaction finite element model (FEM) is created to calculate the upward deformation of the CRTS-Ⅲ track slab caused by the flowing SCC. The main influencing factors, including the SCC’s casting height and speed, SCC’s viscosity, constraint stiffness of the limiting beams, and vertical temperature gradient, have been systematically analyzed and discussed. The relationship between the influencing factors and the track slab’s deformation is obtained. Furthermore, machine learning prediction models using random forest algorithms are developed to evaluate the deformation and up-lift force. A dataset comprising 603 calculation cases obtained from FEM simulations is used to train the prediction models. The random forest-based models developed in this study give an accurate estimation of the deformation and up-lift force based on the SCC properties and construction parameters. In addition, the feature importance of each influencing factor is obtained and studied. The findings of this study can provide guidance for the control of the deformation in CRTS-Ⅲ track slab during the SCC construction process.

Experimental study on interface performance of CRTS Ⅱ slab ballastless track under temperature loading

Interlayer interface damage poses a prevalent challenge in China Railway Track System (CRTS) Ⅱ slab ballastless tracks, with temperature playing a pivotal role in its occurrence. This study aims to scrutinize the mechanism of interlayer interface damage of track structure under temperature loading, vertical full-scale composite specimens were constructed for push-out and normal-tension model tests, and digital image correlation (DIC) technology was adopted to obtain the interlayer strain field distribution during loading and to get the mechanical property degradation, damage evolution law and damage mechanism of cement asphalt (CA) mortar layer interface under different temperatures. Based on the experimental study and fracture mechanics, the temperature cohesion damage model of the track slab-CA mortar interlayer interface was established. The results show that the bonding surface between the track slab and CA mortar layer is particularly susceptible to damage, and the interface damage exhibits "cold brittleness" and " thermal ductility" at low and high temperatures, respectively. Cohesion zone models (CZM) were constructed for both the normal and tangential interfaces at temperatures of 0 °C, 15 °C, 30 °C, 45 °C, and 60 °C. Furthermore, by defining field variables in the ABAQUS software, a temperature variation function describing key parameters of interface damage fracture behavior was integrated into the CZM, using defined field variables. The simulation results exhibited excellent agreement with the experimental findings.

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.

Research on dynamic characteristics of railway side-cracked slab for train-track coupled system

The Ballastless track have been extensively implemented in high-speed railways. However, during the long-term operational process, degradation, such as side crack or defect phenomena produced on the slab inevitably, poses a threat to the stability and the durability of the track structure. Consequently, it is imperative to propose a dynamic approach that can effectively predict the impact of side-cracked slab (SCS) on the vehicle-track coupled system. This paper utilizes co-simulation technology to investigate the dynamic behavior of the slab with and without side crack. Firstly, the dynamic substructure of the finite element model of the SCS is obtained by eigenvalue analysis. Secondly, the SCS model has been applied to the classical vehicle-track coupled dynamic system, and the coupled dynamic model of the train-side cracked slab (TSCS) is established, which considers the multi-rigid-body vehicle subsystem, the flexible rail subsystem, the flexible SCS and subgrade foundation subsystem, and the wheel-rail nonlinear contact model. Later, the accuracy and reliability of the proposed model are verified by the comparison with field tests. Finally, the differences in the vibration characteristics of the vehicle and track structure with and without a side crack are compared and analyzed, and its dynamic stress of the slab as variable train speeds is revealed. The results indicate that the existence of a side crack will reduce the natural frequency of the slab, with a maximum decrease of 22.31%. Although the SCS has a minor effect on the vehicle responses, the existence of a side crack has a significant impact on the slab, especially on the root mean square (RMS) of the vibration acceleration of the slab, with a maximum difference of 74.10% laterally and an increase of 55.16% vertically. Meanwhile, the train speed remarkably affects the crack tip dynamic stress of the SCS, with a maximum increase of 76.07% in the longitudinal direction, 50.34% in the lateral direction and 49.09% in the vertical direction. Higher train speeds will further exacerbate crack propagation under long-term train loading. This study may contribute to the dynamic modeling of TSCS systems and the maintenance of the slab ballastless track.

Field Experiment as a Tool to Verify The Effectiveness of Prototype Track Structure Components Aimed at Reducing Railway Noise Nuisance

The almost unlimited possibilities of modern computational tools create the temptation to study phenomena related to the operation of engineering objects exclusively using complex numerical simulations. However, the fascination with multi-parametric complex computational models, whose solutions are obtained using iterative techniques, may result in qualitative discrepancies between reality and virtual simulations. The need to verify on real objects the conclusions obtained from numerical calculations is therefore indisputable. The enormous cost and uniqueness of large-scale test stands significantly limit the possibility of conducting tests under real conditions. The solution may be an experiment focused on testing features relevant to the given task, while minimising the dimensions of the objects under consideration. Such conditions led to the concept of conducting a series of field experiments to verify the effectiveness of prototype track components, which were developed using numerical simulations to reduce the noise caused by passing trains. The main aim of this study is to examine the acoustic efficiency of prototype porous concrete sound absorbing panels, in relation to the ballasted and ballastless track structures. Presented results of the proposed unconventional experiments carried out on an improvised test stand using the recorded acoustic signals confirm the effectiveness of the developed vibroacoustic isolators.

Study on physical and mechanical properties of cement asphalt emulsified mortar under track slab

PurposeDuring the construction process of the China Railway Track System (CRTS) I type filling layer, the nonwoven fabric bags have been used as grouting templates for cement asphalt (CA) emulsified mortar. The porous structure of nonwoven fabrics endowed the templates with breathability and water permeability. The standard requires that the volume expansion rate of CA mortar must be controlled within 1%–3%, which can generate expansion pressure to ensure that the cavities under track slabs are filled fully. However, the expansion pressure caused some of the water to seep out from the periphery of the filling bag, and it would affect the actual mix proportion of CA mortar. The differences in physical and mechanical properties between the CA mortar under track slabs and the CA mortar formed in the laboratory were studied in this paper. The relevant results could provide important methods for the research of filling layer materials for CRTS I type and other types of ballastless tracks in China.Design/methodology/approachDuring the inspection of filling layer, the samples of CA mortar from different working conditions and raw materials were taken by uncovering the track slabs and drilling cores. The physical and mechanical properties of CA mortar under the filling layer of the slab were systematically analyzed by testing the electrical flux, compressive strength and density of mortar in different parts of the filling layer.FindingsIn this paper, the electric flux, the physical properties and mechanical properties of different parts of CA mortar under the track slab were investigated. The results showed that the density, electric flux and compressive strength of CA mortar were affected by the composition of raw materials for dry powders and different parts of the filling layer. In addition, the electrical flux of CA mortar gradually decreased within 90 days’ age. The electrical flux of samples with the thickness of 54 mm was lower than 500 C. Therefore, the impermeability and durability of CA mortar could be improved by increasing the thickness of filling layer. Besides, the results showed that the compressive strength of CA mortar increased, while the density and electric flux decreased gradually, with the prolongation of hardening time.Originality/valueDuring 90 days' age, the electrical flux of the CA mortar gradually decreased with the increase of specimen thickness and the electrical flux of the specimens with the thickness of 54 mm was lower than 500 C. The impermeability and durability of the CA mortar could be improved by increasing the thickness of filling layer. The proposed method can provide reference for the further development and improvement of CRTS I and CRTS II type ballastless track in China.

Study on the Seismic Performance of High-Speed Railway Extradosed Cable-Stayed Bridge Considering CRTS III Slab Ballastless Track Structure

This paper explores the seismic damping mechanism and performance of CRTS III slab ballastless track on an isolation system extradosed cable-stayed bridge during rare earthquakes. It serves as a guide for designing slab ballastless tracks on high-speed railway extradosed cable-stayed bridges. Using a high-speed railway extradosed cable-stayed bridge as a case study, we established a Midas finite element model to optimize the track plate parameters by adjusting the fastener stiffness and plate joint length. The optimization process and method can be applied as a reference for similar bridge designs. The research findings reveal that, under rare earthquake conditions, the CRTS III slab ballastless track model (with a plate joint length of 90mm and fastener stiffness of 30kN/mm) has a minimal impact on increasing the longitudinal internal force at the pier’s base. It, at most, raises the earthquake internal force response by 5%. The model significantly reduces the overall relative displacement of the bridge pier and girder, with a notable 15.5% reduction in the relative displacement of pier 143# on the side pier. Therefore, when conducting internal force tests for the bridge, it is crucial to consider the influence of track plate restraint.

Mechanical behavior and track geometry evaluation of long-span cable-stayed bridges with ballastless tracks

Ballastless tracks have been widely used in China’s high-speed railways; however, they have only recently been laid on 300 m-class cable-stayed bridges. For cable-stayed bridges with a longer span, the mechanical behavior of ballastless tracks is unclear, and the track construction acceptance method is incomplete, restricting the development of cable-stayed bridges with ballastless tracks. Taking four 300–1000 m-class cable-stayed bridges as research objects, this study established static track–bridge interaction models and dynamic vehicle–bridge coupled models. By evaluating static and dynamic indices, the feasibility of laying ballastless tracks and operating high-speed trains at 350 km/h on cable-stayed bridges was analyzed. Based on the results of dynamic analysis and track geometry evaluation, a 40 m chord was proposed for track geometry acceptance on cable-stayed bridges. The accuracy of the simulation results was verified through the measured data from the Xi-Cheng Railway. The numerical results showed that the 300–1000 m-class cable-stayed bridges with ballastless tracks had good static and dynamic characteristics. The 300 m baseline was unsuitable for the long-wave irregularity evaluation of tracks on cable-stayed bridges, and the 60 m chord was easily affected by wavelengths above 200 m, leading to misjudgment of the evaluation results. The 5 mm limits of the 40 m chord could be used for track geometry acceptance on cable-stayed bridges. Finally, a comprehensive evaluation method for track geometry, namely 10 m chord, 40 m chord, and minimum vertical curve radius, was formed.

Field detection study of the bonding interface bubble defects in the full scale CRTS III slab ballastless track structure

The authors conducted a study on the efficacy of non-destructive testing methods to identify potential bubble defects at the bonding interface, which were a result of the field infusion process in the CRTS III (China Rail Track System III) slab ballastless track structure. Traditionally, these defects were detected through direct observation by the method of on-site uncovering slab. To expedite and enhance the detection of these bubble defects at the bonding interface, the authors were able to obtain fast and effective results via using the impact-echo method. Meanwhile, finite element models were used to construct different scenarios and the presence of the bubble defect would alter the propagation of stress waves inside the structure. Field experiments had shown that when the bonding interface was effectively bonded, the spectra displayed a peak echo signal of maximum amplitude, typically at a frequency ranging between 7000 and 8000 Hz. When bubble defects were present, the peak amplitude of the echo signal would shift to a frequency of around 12,000 Hz on the spectra. The presence of bubble defects at the bonding interface resulted in a rightward shift of the peak amplitude of the echo signal on the spectra.

A monitoring method of rail fastener reaction force based on iron pad strain

This research has successfully explored a monitoring method that does not necessitate modifications to the current structure of the fastening system and ensures that the intrinsic force distribution remains undisturbed, which is the pioneering use of Fiber Bragg Grating (FBG) strain sensors to test the strain of iron pads to reflect the force of fastener support points. Then, through the laboratory single-point loading test and finite element simulation, the feasibility of the monitoring method has been confirmed, and the resolution is higher than the traditional method. Subsequently, based on the experimental environment of high-speed railway commissioning, dynamic long-term monitoring research was conducted, and relevant calibration experiments and finite element simulation analyses were carried out. The experimental research and finite element simulation analysis revealed the superior ability of the method in capturing intricate data details, with the field experiment verifying a high resolution markedly surpassing other existing methods. Furthermore, by monitoring the same train, the data were found to be highly repeatable, which confirmed the ability of the monitoring method to stably reflect the dynamic behavior of the train. Overall, the monitoring method provided in this research could monitor the fastener reaction force in real time for an extended period and accurately record its periodic dynamic loading cycle pattern, which provides important data support for the structural health condition of the ballastless track and the safe operation assessment of trains.