CRTSII Slab Track Research Articles

Time-variant reliability of interlayer damage of CRTS-II slab track by combining the second-order fourth-moment and outcrossing method

This study proposes the combining second-order fourth-moment and outcrossing method for evaluating the time-variant reliability of slab tracks’ interlayer damage. The merit of the method is to improve significantly the computing efficiency and accuracy for the implicit and strong nonlinear limit state function. Furthermore, the effects of narrow joints damage and temperature load on the time-variant reliability of slab tracks’ interlayer damage are investigated. Narrow joints damage is an inducement for the decrease of time-variant reliability index of slab tracks’ interlayer damage, and the index decreases more violently with the increase of temperature rise than that of positive temperature gradient.

Thermal arching and interfacial damage evolution of CRTS-II slab track under solar radiation in alpine and plateau regions

Arch deformation and interface failure of CRTS-II slab track have become crucial issues for the operation safety of high-speed railways. However, few researchers investigated the mechanics and deformation behaviour on CRTS-II slab track exposed to high-altitude plateau climatic environments. This study proposes an analysis approach for thermal arching and interface damage evolution of the slab track structure under solar radiation in alpine and plateau environments. The time-dependent solar temperature distribution is loaded on the refined finite element model (FEM) of the slab track structure’s thermal deformation in high-altitude plateau climatic environments. The analysis approach is validated by comparing the calculated and experimental data. The track slab's maximum and minimum vertical temperature gradient (VTG) are 94.49 °C/m and −45.02 °C/m, respectively. The narrow joint damage is an incentive for the inverted V-shaped thermal arching and interface separation of the slab track structure under solar radiation. The interfacial gap of slab track structure in alpine and plateau regions reaches more than 14 mm during summer. The proposed analysis approach is a valuable reference to the construction temperature, maintenance, and damage monitoring of slab track structure in alpine and plateau regions.

Influence of Uneven Subgrade Frost Heave on Deformation and Damage of CRTSIII Slab Track

The problem of uneven frost heave deformation of high-speed railway subgrade in seasonal freezing areas seriously affects the service state and service life of slab track structures and threatens the safe operation of high-speed vehicles. Based on the damage plasticity theory of concrete, in this study, an analytical model is established for CRTSIII slab track with damage plasticity and reinforcement. The influences of various frost heaving parameters on track structure deformation, interlayer seam, as well as the stress and damage behaviors were analyzed in detail. The results show that, as compared with a linear elastic model, the damage plastic model better reflects the softening behavior and stress attenuation of track structure concrete after reaching its tensile strength. The deformation and the interlayer seam reach their maximum values when the frost heaving wave peak acts at the position that is one-sixth of the base length from the edge of the concrete base. When the frost heaving wave peak acts on grooves at the base center, initially, the track structure is seriously damaged. The interlayer seam and damage decrease with an increase in frost heaving wavelength and increase with an increase in frost heaving wave amplitude. The interlayer seam of the track structure is more sensitive to frost heave deformation having a wavelength of less than 10 m. The extent of damage to the concrete base gradually increases with a decrease in the wave/amplitude ratio. It undergoes three stages of damage evolution: (i) no damage, (ii) upper surface bending damage, (iii) reverse bending damage. In order to improve efficiency, it is recommended, during track maintenance, to focus on the position of the central groove of the base and the position that is one-sixth of the base length from the edge of the concrete base.

Study on Temperature Force Control Mechanism of CRTSⅡ Slab Track: Control Conditions of Temperature Cracking

Study on Temperature Force Control Mechanism of CRTSⅡ Slab Track: Control Conditions of Temperature Cracking

Influence of Uneven Frost Heave of Subgrade on Deformation and Damage of Crts-Iii Slab Track

Influence of Uneven Frost Heave of Subgrade on Deformation and Damage of Crts-Iii Slab Track

Deformation Law and Control Limit of CRTSIII Slab Track under Subgrade Frost Heave

In order to find out the influence of subgrade frost heave on the deformation of track structure and track irregularity of high-speed railways, a nonlinear damage finite element model for China Railway Track System III (CRTSIII) slab track subgrade was established based on the constitutive theory of concrete plastic damage. The analysis of track structure deformation under different subgrade frost heave conditions was focused on, and amplitude the limit of subgrade frost heave was put forward according to the characteristics of interlayer seams. This work is expected to provide guidance for design and construction. Subgrade frost heave was found to cause cosine-type irregularities of rails and the interlayer seams in the track structure, and the displacement in lower foundation mapping to rail surfaces increased. When frost heave occured in the middle part of the track slab, it caused the greatest amount of track irregularity, resulting in a longer and higher seam. Along with the increase in frost heave amplitude, the length of the seam increased linearly whilst its height increased nonlinearly. When the frost heave amplitude reached 35 mm, cracks appeared along the transverse direction of the upper concrete surface on the base plate due to plastic damage; consequently, the base plate started to bend, which reduced interlayer seams. Based on the critical value of track structures’ interlayer seams under different frost heave conditions, four control limits of subgrade frost heave at different levels of frost heave amplitude/wavelength were obtained.

Analysis of Damage of Joints in CRTSII Slab Track under Temperature and Vehicle Loads

Damage in joints has a significant effect on the integrity and stability of the China Railway Track System (CRTS)II slab track. In this study, a three-dimensional finite element model was established to investigate the damage law of joints in the CRTSII slab track under temperature and vehicle loads. In the finite element model, the non-linear constitutive law and damage parameter of the interface between the slabs and the cement asphalt (CA) mortar layer were defined by a cohesive zone model. Based on the limited results in this analysis, the recommendations of joint damage repair were put forward. Results show that in the formation of joint damage in CRTSII slab track, the temperature load plays a more important role compared with the vehicle load. The more the concrete loss at the narrow joint, the lower the temperature rise at which concrete stress reaches its compressive strength. If concrete loss at the bottom of the narrow joint is no more than 10%, the damaged joint can be repaired at the time when the temperature of slabs is close to the construction temperature. If concrete loss at the bottom of the narrow joint is larger than 10%, repair strategy should be taken according to the time when the joint damage is detected. During repair, improving bond strength of the interface between the slabs and the CA mortar layer and strength of joint concrete can help to prevent the repaired joint from being damaged again.

Modeling Slab Track for Vehicle –Track-Coupled Dynamics Analysis Using Spline Function Method

This paper presents a new approach for modeling the slab tracks by using the spline function to derive an element that is capable of describing the vertical motions of the entire slab. The accuracy and advantages of the method are verified through comparison with the finite element method (FEM) by the frequency response analysis for the CRTS-III slab track system. With this, a three-dimensional train–slab track-coupled dynamic (TSTCD) model is developed and solved by a hybrid explicit–implicit time integration method. Finally, the characteristics and feasibility of the developed TSTCD model are demonstrated through two typical case studies together with the comparison made for verifications. The results indicate that the proposed method provides an alternative approach for modeling the slabs, by simplifying the modeling process and decreasing the computational time without losing accuracy, with respect to the FEM. Besides, the modes of the slab appear many dips and peaks above the first resonant frequency, leading to complicated frequency responses of the CRTS-III slab. Moreover, the developed TSTCD model is not only feasible, but also capable of describing the slab vibrations at medium-high frequencies.

Damage Mechanism of Broad-narrow Joint of CRTSII Slab Track under Temperature Rise

There is two typical damage pattern at broad-narrow joint of CRTSII slab track breakage of narrow joint and fracture at junction between broad joint and narrow joint. This paper aims to study the damage mechanism and develop of broad-narrow joint of CRTSII slab track and put forward the methods to reduce the damage. Based on damaged plasticity model for concrete and cohesive zone model, the damage mechanism and development process of broad-narrow joint are analyzed in this study. The unequal width of broad joint and narrow joint, different concrete strength between broad-narrow joints and slab and slab integrity reducing due to the interface are the main reason for the typical damage. It is suggested to set the same width of broad joint and narrow joint, set the same strength of broad-narrow joint and slab and enhance the integrity of the slab by chipping or adding adhesives, among which the former two methods are more effective. Breakage of narrow joint is a gradual compression damage due to the lower concrete strength than slab. Fracture at the junction between narrow joint and broad joint is a mutational tension damage due to the unequal width of broad joint and narrow joint. The temperature gradient has significant effect on the compression damage, but small to the tension damage, it has the risk of complete destruction under extreme conditions.

Arching mechanism of the slab joints in CRTSII slab track under high temperature conditions

China Railway Track System II slab track is widely applied to China high-speed railway. Under the high temperature conditions, it tends to produce different degrees of arch at the joints between prefabricated slabs, which will affect the track irregularity and safe operation of high-speed trains. In this paper, considering the buckling instability of track structure, the arching mechanism of the slab joints was investigated by establishing a 3D finite element model of the CRTSII slab track. Combined with the field investigation, the damage process of joint concrete and its effects on the arching instability were analyzed. The results show: 1) The construction of joint concrete is difficult to control on site, which leads to inferior quality compared to prefabricated slab. The worse quality of joint concrete corresponds to a smaller amplitude of temperature rise causing joints damage and a greater damage area. 2) When the amplitude of temperature rise of the slab is over 37 °C, various damage emerges in the narrow joint and the middle of wide joint, resulting in the eccentric compression. 3) The temperature gradient load will cause the propagation of interface gap between slab and CA mortar layer, which aggravates the arching instability of slab, especially when the height of gap exceeds 1.5 mm. This research is expected to provide guidance for the optimization design, maintenance and damage control of slab track.

Research on Stresses of Narrow Joints Caused by Construction Process of CRTSIISlab Track

A separate finite element model of 1/4 unit track slab of CRTS IIslab track was established for the analysis of the influence of construction process on stresses of narrow joints. When track slabs were connected by tension and when wide joints hardened, the impacts of the longitudinal connection of CRTS IIslab on stresses of narrow joints were analysed. The results show that when track slabs are connected by tension, the bonding states between track slab and mortar layer have little effect on track slab expansion displacement and the re-compression of narrow joints caused by the tensioning force cannot be ensured. If track slabs are connected by tensioning force after the concrete hardening of narrow joints, compressive stresses of narrow joints can be increased by 3.03 MPa. Due to the influence of longitudinal connection of CRTSIIslab, the respective track slab temperature for wide joints hardening Tk and narrow joints hardening Tz are difficult to keep consistent. When wide joints hardened, it potentially makes the compressive stresses of narrow joints zero or very large. In order to keep the narrow joints compressed when wide joints hardened, the measures to control Tz and Tk should be taken to make Tk slightly higher than Tz.

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.

Wide Juncture Cracking Effect on the CRTS II Slab Track

The CRTSⅡ slab track is one of the major ballastless tracks in China. Factors of the design, the construction, the train load and the service environment lead to the wide juncture cracking. The beam-solid model on the elastic foundation was established to carry out the mechanics analysis. Theoretical analysis was made on the influence of the depth and the length of the cracking on mechanical properties of the CRTS Ⅱ slab track. The train load and temperature load can make the increase of the warping of the slab that cause the irregularity of the slab track. When the wide juncture crack completely, the sudden chill can make the slab track crack and effect the quality of ballastless tracks.

Analysis of Cement Emulsified Asphalt Mortar Gap on CRTSII Slab Track under Train Loading

The finite element method was used to analyze the deformation and stress of track in different length and height of gaps under the train load. In order to study the influence of gap between the slab and emulsified cement asphalt mortar of china railway track system II slab track on the subgrade, a model of CRTS II slab track was established on the base of elastic foundation beam theory and finite element software ANSYS. The results show that gap between slab and CA mortar has significance effect on the stress and deformation of track structure. The deformation of rail and slab, the longitudinal stress of slab were increase with the increase of gap length, but has less effect on lateral stress of slab. When the length of gap exceed to 1.95m, the deformation and stress have the tendency of increase sharply, the length of gap between slab and CA mortar should not exceed 1.95m. The gap between slab and CA mortar has effect on the durability and lifetime of ballastless track, so the gap should be maintenance timely.

Mechanical Characteristics Analysis of Type ∏ Terminal Restricted Configuration Transition Section for CRTSⅡ Slab Track

With full-bridge longitudinal-connected foundation plates,CRTSⅡslab track sets type ∏ terminal restricted configuration anchorage structure in the bedroad-bridge transition section,in order to transmit forces such as temperature force and braking force from foundation plate to subgrade. In connection with the deficiency of exsiting researches, through the established finite element analysis model on Type ∏ terminal restricted configuration transition section,its mechanical characteristics under the most unfavorable longitudinal load by changing the structural parameters of transition section are analyzed, focusing on the criterion that the range of maximum of longitudinal displacement is 3mm.Analysis results show that when the longitudinal force is being transmitted to the anchorage structure, the maximum stress and longitudinal displacement of main terminal restricted configuration are far less than the limit and this process has little influence on track geometrical regularity .The laying of sliding layer can ameliorate structural force and deformation. However, changing its friction coefficient has no effect. Moreover, as the soil is under elastic deformation stage, its elastic modulus presents significant effects on mechanical properties of transmit section while its internal friction angle and cohesion have no influence.