Steel Spring Floating Slab Track Research Articles

Investigation of Concrete Damage on a Prefabricated Steel Spring Floating Slab Track by Finite Element Modelling

AbstractTo investigate the concrete damage of prefabricated steel spring floating slab tracks (SSFST), a three-slab prefabricated SSFST system was established using the ABAQUS finite element software. Full trainload conditions and fatigue load conditions of a train passage were successively applied to the system. Plastic damage and fatigue damage of the floating slab were simulated based on concrete damage plasticity theory and model code, respectively. For comparison, a simulation of the fatigue experiment was conducted. Parametric analyses of the concrete strength and isolator stiffness were also performed. The results show that the maximum positive and negative bending moments of the floating slab throughout the loading stage are close in value. The positive bending moment causes stress concentration on the top slab surface which leads to plastic damage and low-cycle fatigue damage, while the negative bending moment causes middle-level elastic tensile stress on the bottom slab surface which leads to high-cycle fatigue damage. Under experimental conditions, damage on the bottom surface is much more severe, while the upper part is undamaged. Improving the concrete strength can reduce both kinds of damage, while increasing the isolator stiffness can only mitigate the high-cycle fatigue damage. Accordingly, recommendations are provided for improving fatigue experiments and structural design of prefabricated floating slabs.This study can inform the design and maintenance of the prefabricated SSFST system, ultimately enhancing their safety and longevity.

Numerical investigation on the failure mode of the upper shear hinge in steel spring floating slab track

Fracture on hinge bars and fixed bolts of upper shear hinges is a common problem in prefabricated steel spring floating slab tracks (SSFST), adversely affecting train operation safety and comfort. To investigate the potential failure modes, this paper established a four-slab SSFST model to analyze the force condition of upper shear hinges. Force transmission between floating slabs as well as the stress level of the hinge bars and fixed bolts under the most unfavorable vehicle cases were respectively simulated by the structural mechanics method (SMM) and the FEA software ABAQUS. Stress influence lines of hinge bars and fixed bolts under the moving vehicle load resulting from ABAQUS were extracted to evaluate the fatigue behavior based on the fatigue S-N curve by the post-processing software FE-SAFE. Furthermore, the influence of different pre-tightening force on fixed bolts’ fatigue behavior was discussed. The results of the two simulation methods match well, suggesting that force between floating slabs is mainly transmitted by rails, while shear hinges only account for about 1/3 of the bending moment and 1/5 of the shearing force. Hinge bars and fixed bolts are both sufficient in strength, yet fatigue problem is likely to happen to the latter. The fatigue failure mode and location of fixed bolts are related to the value of pre-tightening force. Large stress range or high stress mean always exists as the pre-tightening force varies, meaning that bolt fatigue is an intrinsic failure mode of the upper shear hinge in SSFST.

Research on the mechanism of rail corrugation of steel spring floating slab track on metro

Steel spring floating slab track (SSFST) is an effective vibration and noise reduction measure, which is gradually used in urban rail transit in recent years. In order to better solve the problems of vibration noise and abnormal rail corrugation on metro lines, the dynamic model of vehicle-track system including metro vehicle and track structure is established by using the simulation software. The relationship between the passing frequency of vehicle and the vibration frequency of track structure, as well as the resonance characteristics of the elastic track structure are analyzed so as to obtain cause of rail corrugation on SSFST. The results show the following: (1) It is a more obvious resonance phenomenon between the inner rail and the floating slab at the vibration frequency of 116 and 161 Hz (R300 m), 262 Hz (R1000 m) and 320-387 Hz (R1500 m), and the simulation of rail corrugation wavelength is closer to field measured data. (2) Comparing the vibration frequency distribution of ordinary track and SSFST under the same curve radius, the rail corrugation is related to the natural vibration characteristics of track structure. (3) The vibration characteristics of the track structure and the periodic wear characteristics of the rail are the key factors for the formation of rail corrugation.

Component Mode Synthesis Based on the Energy Method for Frequency Domain Dynamic Response Analysis of Ballastless Track Structure

Used extensively in structural dynamics analysis, the energy method is advantageous for transforming boundary value problems of differential equations into variational extremum problems. Recent applications include analyzing the wave and vibration characteristics of track structures. However, traditional energy methods for dynamic modeling and analysis of ballastless track structures require obtaining the global stiffness matrix and mass matrix of the entire coupled system, which decreases computational efficiency. The EM-CMS algorithm for frequency domain dynamic response analysis of ballastless track structures has been proposed to address this issue. The core of EM-CMS is the development of model reduction strategies within the framework of the energy method to reduce matrix dimensions and thereby improve computational efficiency. Specifically, the steel spring floating slab track is the focus of this research. Utilizing the energy functional variational method, the modal properties of the rail and floating slab structures are obtained, and truncation is performed. A reduced-order model for the steel spring floating slab track is established by considering the boundary conditions between the rail-floating slab and the floating slab foundation (connected through fastener springs and steel springs, respectively, and considering the springs’ elastic potential energy). Comparatively, the computational efficiency of EM-CMS is approximately ten times greater than that of the energy method. The method’s accuracy is also carefully validated against finite element simulations.

Mechanism of rail corrugation combined with friction self-excited vibration and wheel-track resonance

In the present study on rail corrugation, a field investigation is carried out on a typical section of a Steel-spring Floating Slab Track (SFST) in the Beijing subway for studying the two distinct types of corrugations generated by the left and right rails in the curved sections of the metro line. Further, study is also done on the vibration response of track components when trains pass over the rail corrugations at a typical SFST curve having small radius of curvature (R = 300 m). The study establishes an SFST rail corrugation analysis model by effectively combining SIMPACK and ABAQUS. The proposed model considers the effects of both, friction self-excited vibration and resonance of the wheel-track system, for analyzing the reasons leading to inconsistent corrugation generated by the left and right rails in the small radius curve section of SFST. The results show that when the train load acts on the middle position of the adjacent steel-spring, it causes the rail to produce vertical bending resonance with the floating slab relative to the baseplate. This, in turn will result in increased corrugation which could reach 200 mm wavelength. At similar frequency, the anti-phase resonance of the unsprung mass and the track vibration mass, directly results in the formation of 200 mm corrugation. The wheelset-SFST system occurs near 68.4 Hz due to vertical torsional resonance of the floating slab. This leads to the rapid development of 200 mm corrugation in the curve's inner rail. When the train passes through the small radius curve section of SFST, the creep force between the guiding wheelset's outer wheel and the outer rail of the curve tends to saturate. This results in generation of 31.5 mm corrugation by the outer rail due to friction self-excited vibration. It is recommended to maintain the vertical stiffness of the fastener system above 50 MN/m to either stop or reduce the generation and development of corrugation at 200 mm and 31.5 mm wavelengths.

An efficient three-dimensional dynamic stiffness-based model for predicting subway train-induced building vibrations

The prediction of train-induced vibration in buildings constructed above the subway is a challenging problem due to its sophisticated system and time-consuming calculation. This paper proposes an efficient three-dimensional (3D) dynamic stiffness-based model (DSM) to predict subway train-induced building vibrations. The DSM has the capability to analytically explore the axial, bending, and torsional vibrations of columns and beams, as well as the flexural and in-plane vibrations of floors and walls induced by the moving train, which few studies have focused on before, and has high computational efficiency compared to the traditional finite element method (FEM). In the DSM, the dynamic stiffness matrices of floors, walls, columns and beams are formulated by the stiffness theory firstly. Then, the global dynamic stiffness matrix of the building is determined following an assembly procedure and the vibration responses of the building can be calculated by the dynamic stiffness equation in the frequency domain. Further, the calculation accuracy and efficiency of the DSM are validated by comparison with a 3D finite element model. Finally, the DSM is used to predict the train-induced vibrations of a building constructed at a subway station based on a subway train-slab track coupled dynamics model. Results show that the building vibrations induced by the moving train are significant in both vertical and horizontal directions and the steel-spring floating-slab track can effectively suppress the train-induced building vibrations.

Experimental study on the vibration reduction characteristics of the floating slab track for 160 km/h urban rail transit

Urban rail transit has been developed rapidly worldwide due to its significant social and economic benefits. At the same time, it is also faced with some key technologies to be solved urgently, such as train speed raise, the impact of train-induced vibration on the track structure and surrounding environment, and the evolution of the vibration reduction performance during long-term service. In this study, the vibration characteristics of the high-speed steel spring floating slab track (HSFST) suitable for a 160 km/h line during fatigue were investigated and compared to that of the ordinary track using full-scale indoor laboratory models. The results show that: 1). After 5 million loading cycles, the change rates of the fastener system stiffness, the track system stiffness, and the damping ratio were 6.7%, −6.6%, and −4.5%. 2). The time-domain analysis showed that HSFST could significantly reduce the amplitude of ground acceleration. Fatigue action has reduced the acceleration amplitude of each track component while increasing the displacement amplitude and vibration attenuation time. 3). The slab-ground subsystem was the main attenuation section for HSFST, which could reduce the vibration energy greatly. The vibration reduction of HSFST (Before cyclic loading) and HSFST (5 million) were 26.3 dB and 24.0 dB. The vibration levels of track components showed an attenuation trend along the longitudinal direction. Although the fatigue loading would aggravate the vibration level, the track system could still play an excellent working performance.

Comparison and analysis of vibration characteristics of different subway tracks

To study the damping effect of different track structures on the environmental vibration, field tests of train-induced vertical acceleration were performed on four types of track structures, namely, ordinary track (OT), medium vibration-damping fastener track (MVDFT), floating-ladder track (FLT) and steel-spring floating slab track (SSFST). The measurement points were set on the rails, track slabs, and tunnel walls. Eventually, the time domain, frequency domain, and one-third- octave frequency division vibration level were adopted to investigate the vibration characteristics of four track structures. The results were obtained as follows. (1) The root-mean-square acceleration values of the four track structures at different measurement points were analyzed in the time domain. Overall, the results could not effectively reflect the damping capacity of the vibration-reduction measures. (2) Based on the one-third octave frequency analysis, regarding 10À6 m/s2 as the decibel reference value, we found that three vibration-reduction measures' vertical vibration level of the tunnel wall was significantly lower than that of OT. Specifically, the damping effect of SSFST was the most obvious. The Z-weighted vibration levels of the three vibration-reduction measures on the tunnel wall have been reduced by 8.919, 11.745 and 13.744 dB, respectively. (3) According to the results of the vibration-transmission characteristics in the frequency domain, the main vibration-frequency regions of the four track structures at the track slab and tunnel wall were all in the range of 1 to 20,00 Hz. Concerning OT, MVDFT, FLT, and SSFST, the peak values of the vibration transmission from the rail to the tunnel wall sequentially decreased, and the damping effect sequentially increased. This paper compared the damping capacity of the above four track structures at 1 to 80 Hz according to ISO 2631-1. In addition, their more detailed vibration characteristics at 1 to 2000 Hz were also considered. It aims to provide a more comprehensive study for the application of subway vibration-reduction measures.

Influence of different track structures on the development of corrugation in small radius curve section of subway

Many studies have shown that the rail corrugation on the small radius curve section of subway floating slab track is serious. And it seems to be different from the rail corrugation on the common track. The track structure must play an important role in the generation and development of rail corrugation. This paper measured a subway line in Tianjin, including 2 different track structures, and analyzed the measured data by using the international evaluation and acceptance indexes of rail corrugation. The results show that the inner rail of short sleeper monolithic track (SSMT) has poor smoothness in the wavelength range of 0-300 mm, and the overall smoothness of outer rail is good; the inner rail of steel spring floating slab track (SSFST) has poor smoothness in the wavelength range of 100-300 mm, and the outer rail has poor smoothness in the wavelength range of 300-1000 mm. Then the vehicle-track coupling model and wheel-rail wear calculation model is established. The calculation results show that in the existing rail corrugation, the short-wavelength rail corrugation of 20-25 mm will continue to appear or deteriorate, and the development of rail corrugation of other wavelengths will slow down or stop to varying degrees; with the increase of train passing times, the rail corrugation of SSFST with the wavelength of 315 mm develops the fastest, and the rail corrugation of SSMT with wavelengths of 20 mm and 160 mm develops the fastest.

Study on the Rail Corrugation at Weld Joint of Steel Spring Floating Slab Track I: Initial Evolution

Study on the Rail Corrugation at Weld Joint of Steel Spring Floating Slab Track I: Initial Evolution

Influence of metro track parameters on vibration characteristics of vibration damping track

In view of the abnormal wear of the vibration damping track with small radius curve on the subway, the vibration and noise problems associated with it have been widely concerned by society. The dynamic model of vehicle-track system including elastic damping track is established by using simulation software. The influence of structural parameters of steel spring floating slab track (SSFST) with small radius curve on the mode and vibration frequency, as well as the resonance characteristics of elastic track structure are analyzed. The results show the following: (1) Increasing the length of floating slab can effectively reduce natural frequency, while the range of frequency variation caused by the thickness of floating slab is relatively small. The length and thickness of floating slab can be properly adjusted to avoid the track resonance. (2) It is more integrated for the rail and floating slab through increasing the vertical stiffness of fastener, which increases the vibration frequency of the track structure. There is little effect on the vibration characteristics of SSFST for changing the installation spacing of steel springs. (3) It is more obvious for resonance to occur between the inner rail and floating slab at 116 Hz, 130 Hz and 161 Hz, and the track vibration mode shows multi-step reverse vibration on both sides and overall vertical bending vibration. (4) Due to the unbalance load caused by curve superelevation, the inner wheel weight plays the restraining role, which makes the inner rail and floating slab have various forms of bending deformation in a certain frequency range, increasing the complexity of the bending deformation of the track structure.

Field Measurement and Mechanism Analysis of Rail Corrugation on Steel Spring Floating Slab Track Section

In this study, a combination method of field measurements and numerical simulations is used to investigate the mechanism of rail corrugation in the curve’s inner rail in urban rail transit. Firstly, field measurements on rail corrugation and rail vibration characteristics were conducted on the steel spring floating slab track (SSFST) section of a metro line; secondly, a three-dimensional finite element model of the wheelset-SSFST was established, and complex eigenvalue analysis and transient analysis were conducted. It was found that the main frequency of measured rail vertical vibration and the simulated wheel–rail—which simulated normal contact force on the inner rail—correspond to the first wheel–rail unstable vibration mode, as well as to the field-measured rail corrugation passing frequency. Therefore, the strong agreement between the results of the field measurements and the numerical simulation further verifies that the frictional, self-excited vibration of the wheelset-SSFST system on a sharply curved track can cause rail corrugation. When the vertical and lateral fasteners’ stiffness increases, the possibility of rail corrugation decreases. The decrease in vertical stiffness of the steel spring leads to an increase in the possibility of rail corrugation, but the lateral stiffness changes in the steel spring have almost no effect on the possibility of rail corrugation. The increase in the wheel–rail contact friction coefficient leads to a sharp increase in the trend of rail corrugation occurrence and causes a decrease in the rail corrugation wave-length.

A parametric study on the structural noise radiation characteristics of a steel spring floating slab track

It is a common experience that the interior noise of an underground train vehicle increases suddenly when it just runs into a track section with steel spring floating slabs, significantly reducing passengers’ comfort. This paper investigates the reasons, and control, of such noise through field tests and model simulations. The effect of rail surface irregularity on interior noise was investigated first by analysing data collected from interior noise tests, rail surface irregularity measurement and by analysing the modal behaviour of the slab. Noise radiation of the track slab was then analysed using the acoustic boundary element method while the vibration of the steel spring floating slab track is predicted based on an infinitely long periodic structure model; And finally with the prediction models, a parameter study was performed for the steel spring floating slab, on the purpose of improving the parameters to make the track less noisy. The research presented in this paper may provide a reference for the design of steel spring floating slabs in terms of noise control.

Experimental Research on Vibration-Damping Effect of Combined Shear Hinge Prefabricated Steel Spring Floating Slab Track.

Objective: The cast-in-place steel spring floating slab track (SSFST) is difficult to maintain and repair, while the mechanical strength of the end of the traditional prefabricated SSFST is poor. In order to overcome the above shortcomings, a shear-hinge-combined prefabricated SSFST was developed, and an indoor test was carried out to analyze its vibration-damping effect. Methods: A combined shear hinge SSFST connection model with two length sizes was established. The dynamic response amplitude and frequency response characteristics of the foundation (ground) under different isolator installations and fatigue loads were studied, and the vibration-damping performance of two sizes of combined shear hinge SSFST was evaluated. Results: The vibration-damping effect of the steel spring vibration isolator mainly acts in the middle and low-frequency bands of 16–400 Hz, and the vibration near 10 Hz will be aggravated after the vibration isolator is installed. The vibration index and variation law of the two sizes of SSFST are similar, and the vibration response of 4.8 m SSFST is slightly less than 3.6 m SSFST. There is almost no change in each index when the load is 5 million times, and there is a certain range of change when the load is 10 million times, but the overall change is small. Conclusions: The combined shear hinge prefabricated SSFST can have an excellent isolation effect on vibration and can still maintain good vibration-damping ability within 10 million fatigue loads (about 5 years); 4.8 m SSFST should be laid in straight sections with higher train speeds, while 3.6 m SSFST should be applied in curved sections to ensure smooth lines.

Design and performance evaluation of piezoelectric tube stack energy harvesters in railway systems

Capturing vibration energy of track structures using piezoelectric energy harvesters has attracted increasing attention for powering wireless sensor networks along railway line. To better use the vertical space below steel rail, a kind of piezoelectric tube stack energy harvesters is proposed in this paper, which can be placed at the bottom of the steel rail to harvest the vibration energy of the vertical displacement induced by the moving train. The harvester consists of a displacement transmission rod, a compression spring, a force transmission metal tube, a piezoelectric tube stack, a whole metal shell, screw bolts, and a wire hole. The advantage of this design is to fully combine the heights of the compression spring, the force transmission metal tube and the piezoelectric tube stack, which helps reduce the vertical height of the device and enables its wide application to a variety of tracks, including, ballast track, ballastless track, and steel-spring floating slab track. Energy harvesting performance of the developed piezoelectric tube stack energy harvester is investigated experimentally, which is consistent with the theoretical results of the simplified model of such a harvester reported. Effects of displacement amplitude, displacement frequency, spring stiffness, resistance, and key parameters of piezoelectric tube stack on the energy harvesting performance of the harvester are also discussed. The present study provides a new design concept for developing piezoelectric energy harvesters used in railway systems with the smaller vertical space below steel rail.

Experimental Research on the Influence of Fatigue Load on the Vibration Damping Effect of Steel Spring Floating Slab Track

Experimental Research on the Influence of Fatigue Load on the Vibration Damping Effect of Steel Spring Floating Slab Track

UM-SIMULINK Co-simulation for the vibration reduction optimization of a magnetorheological damping steel-spring floating slab track

To further mitigate the low-frequency vibration of a vibration source induced by the natural frequency vibration of a floating slab track (FST), the key parameters including the maximum damping force and the displacement threshold of magnetorheological dampers (MRDs) were studied under different subway operating conditions. A Graphical user interface (GUI) co-simulation was proposed to investigate the dynamic responses of a magnetorheological damping Steel-spring FST (SSFST). The mitigation effect of different MRD parameters on vibration sources was evaluated with the environmental vibration prediction model. MRDs could reduce the Z-weighted vibration level of the FST and the tunnel wall simultaneously, but the control strategy was necessary to prevent excessively amplifying the mid-high frequency vibration of the tunnel wall. The deterioration of the track irregularity and the train characteristic frequency close to the natural frequency of the FST required an appropriate increase in the MRD maximum damping force. The displacement threshold should be determined in combination with the dynamic displacement generated by the axle load and the corresponding vibration reduction effect. When the same desired effect is obtained, the parameter matching with a smaller MRD damping force and a larger displacement threshold is recommended.

A theoretical vibration‐reduction effect analysis of the floating slab track supported by nonlinear variable stiffness isolators and semi‐active magneto‐rheological dampers

Nonlinear vibration control theory has resolved some bottleneck problems that cannot be solved by traditional linear vibration control theories. In this study, intelligent controllable magneto-rheological dampers (MR-Ds) and high-static-low-dynamic variable stiffness vibration isolators (VS-VIs) are innovatively applied to a traditional steel-spring floating slab track (FST) to improve its low-frequency vibration-reduction effect. To determine the reasonable parameter group of the VS-VI and the parameter matching when used with MR-D, parameter groups were first preliminarily proposed through static and dynamic analyses of the equivalent single-degree-of-freedom (SDOF) model of the FST. A vertical vehicle–variable stiffness-magneto-rheological FST coupled dynamic model was established, and the parameter group was optimized based on safety and vibration-reduction analyses. The simulated results showed that the positive and negative stiffnesses were the key parameters that determined the stiffness nonlinearity level and dynamic support capacity of the VS-VI. Improving the positive stiffness is necessary to achieve a low-dynamic stiffness under no vehicle load and to ensure the millimeter-level dynamic displacement of the FST under vehicle load. An appropriate stiffness nonlinearity level can achieve a better vibration-reduction effect, and excessive nonlinearity level will not bring more significant improvements. The damping ratio in the dynamic analysis is a key parameter to prevent the jumping phenomenon, and the recommended value should not be less than 5%. Moreover, when the VS-VI and the MR-D were efficiently incorporated, a smaller MR damping force and larger displacement threshold could not only achieve a better vibration-reduction effect but also reduce the energy consumption.

Dynamic characteristic difference of steel-spring floating slab track between single-carriage and multi-carriage models

The steel-spring floating slab track (SSFST) is a low-stiffness structure, sensitive to the vehicle loads. Due to the coupling effect of the superposition of adjacent bogies, it is difficult for conventional single-carriage models to meet the simulation requirements. To find a balance between computation efficiency and authenticity of analytical model results, the influence of carriage number on SSFST should be studied. Based on the finite element method and multi-body dynamics, a refined three-dimensional coupled model of multi-carriage-SSFST-tunnel was established. The difference in the dynamic response of the SSFST between single-carriage and multi-carriage models was analyzed and compared with the measured data. The field test results show that structural displacements and accelerations under the two-carriage model are much closer to the measured data. The dynamic model analysis results show that the maximum displacement of the rail and SSFST in the midspan of the slab increase by 0.48 mm and 0.34 mm under the multi-carriage model, and the vibration reduction effectiveness increases by 1.4–2.0 dB. Dynamic responses of the rail and SSFST show minor differences under the two-carriage and three-carriage models. The article is expected to provide a reference for the theoretical research, design, and layout optimization of subway SSFST.

Vibration response analysis of floating slab track supported by nonlinear quasi-zero-stiffness vibration isolators

To improve the low-frequency vibration reduction effect of a steel spring floating slab track (FST), nonlinear quasi-zero-stiffness (QZS) vibration isolators composed of positive stiffness elements (PSEs) and negative stiffness elements (NSEs) were used to support the FST. First, considering the mechanical characteristics of the nonlinear QZS vibration isolators and the dynamic displacement limit (3 mm) of the FST, the feasible parameter groups were studied with the nonlinear stiffness variation range and bearing capacity as evaluation indices. A vertical vehicle-quasi-zero-stiffness floating slab track (QZS-FST) coupled dynamic model was then established. To obtain a reasonable nonlinear stiffness within a few millimeters, the original length of the NSEs must be analyzed first, because it chiefly determines the stiffness nonlinearity level. The compression length of the NSEs at the equilibrium position must be determined to obtain the low stiffness of the floating slab without vehicle load. Meanwhile, to meet the dynamic displacement limit of the FST, the PSE stiffness must be increased to obtain a higher stiffness at the critical dynamic displacement. Various stiffness groups for the PSEs and NSEs can provide the same dynamic bearing capacity and yet have a significantly different vibration reduction effect. Excessive stiffness nonlinearity levels cannot effectively improve the vibration reduction effect at the natural frequency. Furthermore, they also significantly amplify the vibrations above the natural frequency. In this paper, the vertical vibration acceleration level (VAL) of the floating slab and the supporting force of the FST can be decreased by 6.9 dB and 55%, respectively, at the resonance frequency.