Slab Ballastless Track Research Articles

Track and ground vibrations generated by high-speed train running on ballastless railway with excitation of vertical track irregularities

Track irregularities generated during the running service of high-speed railways aggravate vibrations of the track and the surrounding ground environment. To better understand the propagation of vibrations induced by high-speed train running on irregular tracks, a 2.5-dimensional (2.5D) finite element model combining with thin-layer elements was applied to establish a vehicle–track–foundation coupled dynamic analysis model. A quarter-car model was used to derive the equation for wheel–rail interaction force considering track irregularity. The track structure and the underlying foundation were simulated using the 2.5D finite element model, and the subsoil boundary was simulated using thin-layer elements. Compared with the field measurements of the Beijing–Shanghai high-speed railway, the reliability of the established numerical model in analyzing vibration response was verified. A spectrum analysis of the response data obtained from the field measurements reveals that for a newly constructed high-speed railway, track alignment is in good condition due to the operation of grinding and leveling, and vehicle parameters dominate the vibration response of the track structure. Then influences of track irregularities of four typical wavelengths on the vibrations of the track and the surrounding ground environment were investigated. It is found that track irregularities of smaller wavelengths induce higher vibration frequencies and significantly higher vibration responses from the track and the ground compared to track irregularities of longer wavelengths. However, the low-frequency vibrations induced by the latter propagate to a longer distance compared to the former. The critical velocity of the ballastless slab track–ground system is greater than the Rayleigh wave velocity of the soft layer of the subsoil. When train speed is lower than the critical velocity, track irregularity substantially affects the vibrations of the track and the surrounding ground. When the train speed exceeds that critical velocity, the ground vibration is determined by the train wheel weight.

Temperature sensitivity and model of stress relaxation properties of cement and asphalt mortar

The stress relaxation properties of two types of cement and asphalt mortar (CA mortar) in the temperature range of −40 to 60°C and at the initial strain of 0.1% was studied by dynamic mechanical thermal spectrometer. The results show that the stress relaxation process of CA mortar can be divided into attenuation stress relaxation stage and steady stress relaxation stage. The lower the temperature is, the higher the initial stress and residual stress are. At the same temperature, the stress relaxation rate and specific stress relaxation of type I CA mortar are larger than that of type II CA mortar, while the initial stress, residual stress and stress relaxation modulus are relatively smaller. The glass transition region of type I CA mortar characterized by the isochronous stress–temperature curves is −20 to 0°C. The established model agrees well with experimental results, and φ, δ are dominated parameters affecting the stress relaxation of CA mortar. This indicates that the established model can effectively predict the time dependence and temperature sensitivity of stress relaxation of CA mortar. The results can provide reference for the calculation of temperature stress of CA mortar filling layer of ballastless slab track.

An experimental study of the insulation performance of ballastless track slabs reinforced by new fiber composite bars

Due to inductive impedance caused by steel meshes in traditional reinforced ballastless track slabs, the electric properties, primarily rail resistance and inductance, of the track circuit are affected by electromagnetic induction between the slabs and the electric current in the rail. This problem results in poor transmission performance through the track circuit. Insulating heat-shrinkable sleeves between the steel meshes have been used to improve the insulation capability of steel meshes in slabs; however, they reduce the bonding performance between the steel bars and concrete. Because of the highly insulating properties of fiber reinforced polymer (FRP) and steel-fiber reinforced polymer composite bar (SFCB), these composite materials have shown promise to overcome the insulation problem. In the study reported in this paper, single and double layer meshes and ballastless track slabs were manufactured and tested for the first time. In the research reported herein, basalt fiber reinforced polymer (BFRP) and SFCB were used in meshes and slabs, respectively. The electric properties of the rail affected by these meshes and slabs were investigated and compared with steel meshes and ordinary reinforced ballastless track slabs (RC). As the test results demonstrated, the signal frequency and distance between the slabs or meshes and the rail had a significant impact on the electric properties of the rail. Furthermore, the variation in rail resistance induced by the slabs or meshes increased drastically, while the change in rail inductance increment varied slowly. BFRP and SFCB used as transverse reinforcement of slabs or meshes reduced the variation in the electric properties of the rail. BFRP reinforced ballastless track slabs had the highest insulating performance, while those with SFCB demonstrated the second highest performance.

Rheological Behavior, Segregation, Microstructure, and Construction Quality of Cement-Emulsified Asphalt Mortar with Associative Thickener

AbstractCement-emulsified asphalt mortar (CAM) is a critically important engineering material for a slab ballastless track. Segregation, which results in a density difference between the upper and lower part of the hardened CAM, is the most important factor that affects construction quality in practice. With the aim of decreasing the segregation of CAM, a minute amount of associative thickener, in which the mass ratio of the thickener to emulsified asphalt was 0, 0.2, 0.4, 0.6, 0.8, and 1.0%, respectively, has been incorporated into CAM, and the effects were systematically studied in terms of rheological behavior, segregation, microstructure, and construction quality of CAM. The results showed that the segregation resistance of hardened CAM was dramatically improved by increasing the thickener, whereas the rheological behavior characterized by the workability and fluidity indexes was prone to worsen. Considering the technical and economic aspects, an optimum mass ratio of the associative thickener to emul...

Experimental Study on Vertical Stiffness of WJ-8 Fastener for High-Speed Railway

The rail vertical displacement of CRTSII slab track structure under vertical static loads was analyzed in this paper by using 1:1 full-scale track model, based on which the WJ-8 fastener vertical static stiffness was calculated, and the rationality of the fastener vertical stiffness values and the relationship between the values and load were studied. According to the beam-plate theory and beam-solid theory for slab ballastless track, a finite element analysis model of CRTSII slab track structure was established. The rail vertical displacement under the same case as test was calculated by using the measured fastener vertical stiffness value. The rationality of the method for testing and the fastener vertical static stiffness is verified through comparing the calculated values with experimental ones.

Structural performance of ballastless track slabs reinforced with BFRP and SFCB

Because of the inductive impedance caused by steel meshes in traditional reinforced ballastless track slabs, the electricalproperties, primarily the rail resistance and inductance, of jointless track circuits are affected by electromagnetic induction between the slabs and the electric current in the rail. This problem results in poor transmission performance throughout the track circuit. Insulating sleeves or cards between the steel meshes have been used to improve the insulation capability of steel meshes in slabs; however, they reduce the bonding performance between the steel bars and concrete. Because of the good insulation properties of fiber-reinforced polymer composite bars (FRPs) and steel-fiber reinforced polymer composite bars (SFCBs), these composite materials have shown potential to overcome this insulation problem. However, the structural performance of the ballastless track slabs reinforced by basalt fiber reinforced polymer composite bars (BFRPs) and SFCBs, which play a key role in the structure and transportation safety, needs to be investigated. In this paper, six ballastless track slabs reinforced with BFRPs, SFCBs, and steel bars were constructed and tested. The following results were obtained. (1) Shear failures were observed for all slabs, both the BFRP and SFCB slabs meet the load level requirements, and SFCBs reinforcements have higher strength utilization compared with BFRPs reinforcements. (2) The bond-quality of SFCBs and BFRPs reinforcements proved slightly poorer than that of the steel bars. Because of the good corrosion resistance of the FRP, the maximum crack width limits can be slightly larger than that of the RC slabs. (3) Bischoff’s equation was initially used to calculate the deflection of partially prestressed concrete slabs under service loads. The results demonstrated a good agreement between the theoretical and experimental analysis. (4) Considering the tensile stiffness, the modified ACI equation was used to calculate the slabs’ crack width and the theoretical and experimental results showed a good agreement.

A new two-staged model to predict corrosion degree of steel bars in cracked concrete area

In order to quantitatively describe the local corrosion process of steel bars in cracked concrete area, a new two-staged utility model is established, and the effect of transverse cracks on the reinforcement corrosion is analyzed from the angle of long-term service performance evaluation for reinforced concrete structure. Moreover, based on the principle of spectral analysis for environmental action of concrete, an equivalent relationship is established between the corrosion rate in the natural environment and that under the standard temperature and relative humidity condition according to the principle of equivalent annual corrosion depth. Comparison between the inspection results from some references and the calculated values by the two-staged utility model validates the feasibility of the proposed model. The model was applied to Chinese Railway Track System (CRTS)II ballastless track slab with transverse dummy joints, from which satisfactory results of corrosion degree of steel bars were obtained.

Full-scale model testing on a ballastless high-speed railway under simulated train moving loads

Model testing in laboratory, as an effective alternative to field measurement, provides valuable data to understand railway׳s dynamic behaviors under train moving loads. This paper presents comprehensive experimental results on track vibration and soil response of a ballastless high-speed railway from a full-scale model testing with simulated train moving loads at various speeds. A portion of a realistic ballastless railway comprising slab track, roadbed, subgrade, and subsoil was constructed in a larger steel box. A computer-controlled sequential loading system was developed to generate equivalent vertical loadings at the track structure for simulating the dynamic excitations due to train׳s movements. Comparisons with the field measurements show that the proposed model testing can accurately reproduce dynamic behaviors of the track structure and underlying soils under train moving loads. The attenuation characteristics of dynamic soil stresses in a ballastless slab track is found to have distinct differences from that in a ballasted track. The model testing results provide better understanding of the influence of dynamic soil–structure interaction and train speed on the response of track structure and soils.

Dynamic mechanical properties of cement and asphalt mortar based on SHPB test

In order to study dynamic mechanical properties of cement and asphalt mortar (CA mortar), the compressive stress–strain experiment of CA mortar at intermediate strain rates was carried out by split Hopkinson pressure bar (SHPB). The experimental results show that the peak strength of CA mortar increases with the increase of strain rate, and the growth rate decreases gradually. The discrete dynamic Young’s modulus is 19.04–380.82times as big as that at the quasi-static loading rate. The specific energy absorption of CA mortar increases exponentially with the increase of strain rate. Dynamic constitutive model of CA mortar was established, and agreed well with experimental results. The parameter m mainly influences the peak strength of constitutive model, the peak strength increases with the increase of m. While the parameter n mainly influences the descent velocity of stress of constitutive model after peak strength, and the bigger n is, the bigger the descent velocity is. The study results can provide theoretical reference for the structural design of ballastless slab track.

Creep properties of cement and asphalt mortar

In order to study the long-term deformation properties of cement and asphalt mortar (CA mortar), the creep properties of CA mortar on different load levels were studied by independently designed creep testing apparatus. The experimental results show that the creep deformation of CA mortar can be divided into the attenuation creep stage in which the deformation rate decreases gradually and the steady creep stage in which the creep rate is relatively stable. The greater the load is, the bigger the deformation rate and the creep deformation in every stage are. The specific creep of type I CA mortar is bigger than that of type II CA mortar. The long-term strength of two kinds of CA mortar is 0.4σp which is calculated by the method of isochronous stress–strain curves. A creep model of CA mortar based on the thermodynamic theory is established, and the correlation coefficients between fitting results of model and experimental results are all greater than 0.98. The study results can improve the structural design theory of ballastless slab track.

Study on the Resistance to Water of CA Mortar Used in CRTSII Ballastless Slab Track

This paper studied mechanical properties and microscopic changes of CRTSⅡtype CA mortar under the roles of the conditions of water immersion, acid soaking, wet and dry cycling, etc. The results show that: under the role of water immersion, the relative compressive strength decreases and elastic modulus decreases firstly and then increases with the extension of the time; under the role of acid soaking, the relative compressive strength and elastic modulus both decrease with the extension of the time; under the role of wet and dry cycling of short period, the relative compressive strength and elastic modulus both decrease with the increasing of cycling times, but CA mortar exists serious brittleness phenomenon under the role of wet and dry cycling of long period.

Temperature Field Analysis of CRTS-II Ballastless Track Slab Structure on Soil Subgrade

Temperature changes have a significant impact on the CRTS-II track structure in Beijing-Shanghai high-speed railway which has longitudinally connected type. In this paper temperature fields of ballastless track superstructure are simulated based on heat transfer theory and subroutine of ABAQUS that solar radiation DFLUX and ambient temperature FILM. The results showed that: the maximum temperature difference on the top of track slab is 20°C in summer and 10°C in winter; the maximum temperature difference in CA mortar layer is 4°C in summer and 2°C in winter; the maximum temperature difference in concrete substrate is 2°C in summer and 1°C in winter.

Study of the Effect of Cement Asphalt Mortar Disease on Mechanical Properties of CRTS II Slab Ballastless Track

This paper built the three dimension mechanics model of CRTSII slab ballastless track structure on subgrade with ANSYS software. Analysis the influence of deformation and stress characteristics caused by different temperature gradients and the coupling action of temperature gradients and train loads under different work conditions, including no-separated, separated, and multiple-slabs separated with the cement asphalt mortar layer. The results show that, temperature gradients on track slab is one of the main reasons which caused the gap appearing between the bottom of slab track and cement asphalt mortar elastic cushion. And the joint main cause the deterioration of vibration of track slab, accelerating the deterioration of the cement asphalt mortar layer.

Analysis of Vibration Reduction Properties of Rail Damping under High-Speed Vehicle Moving Load

Rail damping is an active and effective control method for mitigating railway vibration and noise at the source. In order to investigate the applicability of rail damping to high-speed railway, a vehicle-ballastless slab track-bridge coupling dynamic model was established and the vibration reduction effect of rail damping at bridge mid-span, bridge pier and beam gap under a high-speed vehicle moving load was analyzed. The results show that: the max vibration acceleration of ballastless track and bridge with rail damping are obviously decreased, and the duration time of structure vibration is also shortened. The vibration reduction effect of rail damping at bridge mid-span is more significant than that at bridge pier. In the working frequency range of rail damping, the acceleration vibration level of the rail can be reduced by 2–5dB, and the vibration of ballastless track slab and bridge also can be decreased in middle and high frequency range.

PFC’s Application on the Dynamic Response Analysis of High Speed Railway Ballastless Subgrade

The biaxial test on ballastless track subgrade material of surface layer and bottom layer of subgrade was established using the particle flow code(PFC). Based on the micro parameter gotten from the biaxial test, a two-dimensional discrete element model of slab Ballastless Track subgrade is modeled. The dynamic response under dynamic load was calculated. A comparison of simulation results and the field measured data shows goodness of fit which provides a new way of simulation on dynamic response of high speed railway subgrade.

Effect of Cement Asphalt Mortar Debonding on Dynamic Properties of CRTS II Slab Ballastless Track

The debonding of cement emulsified asphalt mortar (CA mortar) is one of the main damage types in China railway track system II slab ballastless track. In order to analyze the influence of mortar debonding on the dynamic properties of CRTS II slab ballastless track, a vertical coupling vibration model for a vehicle-track-subgrade system was established on the base of wheel/rail coupling dynamics theory. The effects of different debonding lengths on dynamic response of vehicle and track system were analyzed by using the finite element software. The results show that the debonding of CA mortar layer will increase the dynamic response of track. If the length of debonding exceeds 1.95 m, the inflection point will appear on the vertical displacement curve of track. The vertical vibration acceleration of slab increases 4.95 times and the vertical dynamic compressive stress of CA mortar near the debonding region increases 15 times when the debonding length reaches 3.9 m. Considering the durability of ballastless track, once the length of debonding reaches 1.95 m, the mortar debonding should be repaired.

Research on Measures of Restraining the Vertical Deformation of CRTSII Ballastless Track Slab as Filling Cement Asphalt Mortar

CRTS II ballastless track slab tend to generate vertical deformation when filling cement asphalt mortar. The phenomenon mentioned above leads to higher probability of generating joints between track plate and cement asphalt mortar. Based on the finite element theory, a mechanical model that contains track plate, supporting slab, cement emulsified asphalt mortar and withhold device is established. The purpose of such a model is to research the interaction among components as well as simulate the exact CRTSIIballastless track structure. By analyzing the influences of various trackway conditions, cement asphalt mortars filling height and withhold device arrangement on vertical differential deformation of track plate, put forward the measures to restrain the vertical deformation of track plate. The research results provide references for the ongoing ballastless track construction on the Shanghai-Kunming passenger dedicated line.

Research on CRTSIII Ballastless Track Slab Cracks of High-Speed Railway

At present ballastless track has been widely applied to railway line for passenger in our country, therefore it has broad prospect. Cracks in ballastless track slabs are inevitable in the construction and operation of high-speed railway. Based on comprehensive investigation of documents, and taking cracks in ballastless track slabs as the main object, systematic and deep research has been done within this paper. The main research contents are as follows: First of all, the structure characteristics of CRTSIII ballastless track in high-speed railway are briefly introduced; Secondly, the paper mostly introduces the impacts what cracks make, the characteristics of cracks and how they form. Subsequently the paper introduces what are made to prevent cracks.

The Analysis of Vibration for Ballastless Track-Bridge Base on a Hybrid FE-SEA Method

In this study, the methods for combining statistical energy analysis (SEA) and the finite element method (FEM) for the vibration analysis of structures are studied. Using the two methods simultaneously isnt entirely extend a primarily low frequency method, the finite element method, and high frequency method, SEA, to the mid frequency region are addressed. This approach is intended to extend the frequency range for a FEM based vibration analysis . A new finite element elementl for elevated slab ballastless track is proposed in which the new model can be used for modeling the track structural constituents of elevated slab ballastless track. Using finite element method and Hamilton theory, the coupled equation of vehicle-track-bridge can be established. In calculating example, both the rail displacement induced by single four-layer beam model. Specifically, it showed that the method yields very good result and high performance in the numerical example of previous research.

Stress and Deflection Parametric Study of High-Speed Railway CRTS-II Ballastless Track Slab on Elevated Bridge Foundations

Ballastless track slab system (BTS) of China Rail Transit Summit type-II (CRTS-II) is primarily used in China’s Beijing-Shanghai high-speed railway. As a new structural form, CRTS-II has not been extensively tested, and the design and manufacturing processes of CRTS-II BTS systems is not optimized and mature for its load-carrying capacity, structural integrity, deflection, and durability. This study carried out a numerical analysis of stress and deflection responses of the CRTS-II BTS system using SAP 2000. Design parameters include stiffness of the rail fastening, thickness and stiffness of the track slab, the cement emulsified asphalt (CA) mortar cushion, and the concrete supporting layer. Deflection, maximum bending stress, and maximum shear stress of different structural components of the CRTS-II BTS system are investigated under varying design parameters, with the aim to explore an improved set of design parameters. The rail defection is only significantly impacted by the rail fastening stiffness. To reduce the high-speed rail deflection so as to mitigate riding discomfort, higher stiffness of the rail fastening is suggested. To reduce the track slab bending stresses to prevent the high-speed rail from structural failure, the following parameter design strategy can be used: higher track slab thickness, lower track slab stiffness, lower rail fastening stiffness, higher CA mortar, and concrete supporting layer stiffness. All design parameters of the BTS system have negligible influence on the maximum bending stress and shear stress of the elevated bridges. The maximum shear stress of the BTS system is relative low compared with the maximum bending stress of the BTS system, suggesting that the BTS system behaves more like a beam rather than a plate.