Rail Support Research Articles

Two-axle test vehicle for damage detection for railway tracks modeled as simply supported beams with elastic foundation

For damage detection of railway tracks, a two-axle test vehicle is better than a single-axle vehicle due to its capability of self standing and stability. This paper presents a new, comprehensive theoretical framework for a two-axle test vehicle moving over railway tracks modeled as a simply supported beam with elastic foundation. Firstly, closed-form solutions for both the vehicle and rail responses of the system were derived, along with those for the two contact points by a back calculation procedure. Secondly, the driving component of the contact-point response was processed by the Hilbert transform to yield the Instantaneous Amplitude Squared (IAS) for damage detection. Then, the efficacy of the proposed technique was numerically validated by the Finite Element Method (FEM). Particularly, the sensitivity of the proposed technique was investigated against various factors, including the damage severity, multi damages, vehicle speed, track unevenness, track damping, and measurement noise. The result shows that the IAS of the driving component of the contact point response of the railway track is a good damage indicator in that it is of low frequencies and narrow band, while its modal amplitude is sensitive to the stiffness loss in rail supports.

Prediction of building vibration induced by metro trains running in a curved tunnel

Curved metro lines currently account for a significant proportion of total route mileage. However, the existing prediction model of environmental vibration only considered the vibration induced by trains running in a straight tunnel. In the present study, a numerical model was proposed to predict the environmental vibration induced by trains running in a curved tunnel. The model was divided into two parts: a train–track coupled model and a tunnel–soil–building finite element model. In the first part, a novel three-dimensional train–curved track coupled model was established and solved in the frequency domain based on the periodic theory. Both vertical and horizontal train loads were calculated by this model. Then, an in situ measurement was performed in the curved tunnel of an operating metro line, and the tunnel vibration responses were obtained and used to calibrate the train–track model. Finally, a case study was selected from Beijing metro line 16, where it is needed to predict and evaluate the environmental impact of vibration from a curved metro line being planned for construction beneath an office building. A three-dimensional tunnel–soil–building finite element model was built, and the building vibrations in vertical and horizontal directions were predicted. The results show that the floor vibrations have peak values of approximately 5.29 and 27.8 Hz, which are exacerbated by the building local mode and the spacing of the rail supports. Below the third floor, the vertical vibration response exceeded the vibration control limit recommended by Chinese national standards. Track solutions for vibration control must be implemented to mitigate the environmental vibrations.

Experimental and numerical investigation of damage development in embedded rail system under longitudinal force

Embedded rail system (ERS) is a new type of track structure with many advantages due to its continuous rail support. The rapid development of urban rail transit all over the world renders its application prospect broad. However, the cracks and debonds in ERS present a threat to the traffic safety and a possibility for high maintenance costs. In this work, a longitudinal pushing experiment was designed to explore the damage development process in ERS in order to help structural optimization and performance maintenance. The first order derivative of displacement-longitudinal force curve indicates that the damage process of ERS could be divided into three stages: linear elasticity, damage initiation and damage acceleration stages. The surface deformation of the elastic poured compound (EPC) was analyzed with the particle velocimetry and it is shown that the damage is possibly localized in a small EPC part. Statistics of the absolute displacements of a large number of interrogation areas show that their percentage distribution changes in agreement with the increment of rail displacement, which could be the basis for monitoring of EPC deformation in the breathing zone of continuous welded rail. The analysis of the deformation of EPC from side views, together with the qualitative analysis with finite element method, reveals that the large shear strain of rubber strip and the intense shear strain of EPC at rail foot are the main causes of damage initiation and growth in ERS under longitudinal force.

Vibration Analysis of Coupled Multilayer Structures with Discrete Connections for Noise Prediction

It is often necessary to calculate the vibration of noise from multilayer structures comprising several substructures coupled with discrete connections. A dynamic flexibility method (DFM) is adopted to decouple the multilayer substructures, which allows the interface forces among the substructures to be directly solved using a linear equation of deformation compatibility. The structural vibrations and power flows into each substructure can then be calculated. To illustrate the use of the DFM, a coupled train–track–bridge system for urban rail transit traffic is investigated as a case study. Two infinite plate models are used to model the U-shaped bridge substructure to improve the computing efficiency compared with the finite element models in calculating high-frequency vibration. The applicability of the infinite plate models is discussed in terms of various rail positions on the bridge, the thickness of the rail support blocks, and multiple wheels that interface with the rail. The results show that the Mindlin plate model has similar accuracy but much greater computing efficiency than the finite element models. With the vibration results from the DFM, the associated wheel–rail noise and structure-borne noise from the bridge are then calculated together with a 2D acoustic model. Good agreement is observed between the predicted noises and the measured data.

Research into the track/vehicle interaction processes for underground railways

The article deals with determination of dynamic forces in interaction between a rail vehicle and underground track for working out recommendations in terms of a longer service life of the permanent track without extra charges. The issue is of importance for enterprises under limited resources. The research was conducted with mathematical model methods for the vehicle/track dynamic system (the principles were developed earlier), as the experimental work in the underground tunnels was complicated by intensive train traffic during a day. A special feature of the research was consideration of a rail as a bar rested on discrete elastic-dissipative supports in a design diagram of the vehicle/track dynamic system. Thus, the authors established the effects of unequal elasticity of the track rail support on the value of vertical dynamic forces when a metro coach moves on the track. In particular, the dependencies of dynamic factors and amplitude ratios of vertical forces on speeds of metro coaches along the discrete elastic- dissipative track were obtained. An exceptional value of the research is consideration of both vertical and horizontal lateral forces on the vehicle/track interaction. It allowed the authors to define the value of vertical and horizontal lateral forces which occurred when metro coaches moved along straight and curved sections of the track according to the speed and curve radius.

Modeling the Dynamic Response of Railway Track

The authors developed a model based on the dynamical theory of elasticity, which allows us to describe the dynamic equilibrium of strains of the railway track layers. The model of the stress-strain state for the railway track consists in a combination of the geometry equations of the outline of a part in the system’s space, involved into interaction at a given time and the equations of the dynamic equilibrium of its deformation. Considering the obligation to register the course of the process in time, for each time step of integration the outline of the strains propagations front is determined. The strains propagations front is described by the equations of propagation in the material of the elastic spatial wave of oscillations. It allows determining complete spatial-temporal account of the deflection dynamics of the rail support, which enables the execution of calculations, including for conditions of fast-speed and high-speed trains. With the application of the developed model, a number of scientific and practical problems were solved.

Estimation and test assessment of the rail pads effect on the indicators of dynamic impact of the rolling stock on the track in the joint area

Increasing axial loads including the development of heavy movement on Russian railroads network require the best solutions for improvement of the railway track structure. Research by Russian and international scientists indicates that rail elastic pads reduce vibrations transferred from reinforced concrete sleepers to crashed stone, including the joint area. This study examines possibilities of using rail pads for reducing the dynamic effects of the rolling stock on the track in the joint area. Assessment of the rail pads construction material shock-absorbing properties was conducted considering the elastic properties of the rail support with static and dynamic loads. Results of mode ling the elastic properties of the rail support with rail pads of different rigidities using the software complex “Universal mechanism” are presented. The results were used as basis for calculation of indicators of dynamic interaction of the track and rolling stock at the joint using the coeffi cient establishing the link between bendings of the solid rail and the rail with joint. The expediency of using rail pads at the place of the joint is justifi ed based on assessment of the results.This study reveals that elastic rail pads based on isoprene rubbers are suitable for track structures that improve indicators of the track and rolling stock interaction. When using rubber pads, the growth of accelerations on the sleeper is less dependent on the speed, causing the track stability to increase. The results are supported by tests consistent with calculations and justify the necessity for further studies in this fi eld.

레일지지점 간격 및 교량받침위치에 따른 철도교량 단부의 거동분석

본 연구에서는 철도교량 단부 콘크리트궤도에서 레일지지점 간격 변화와 교량받침 위치변화가 레일체결장치에 미치는 영향에 대하여 연구를 수행하였다. 레일지지점 간격은 600mm와 750mm를 고려하였고, 교량받침위치(교량 받침축과 마지막 레일지지점과의 거리)는 750mm와 935mm로 선정하여 철도교량 단부 거동 모형시험을 수행하였다. 철도교량 단부 거동 모형시험에서 거더의 휨 변형(단부 회전)에 따른 거더 단부, 레일, 레일체결장치의 변위를 확인하기 위하여 각 위치에 변위계를 사용하여 계측하였다. 또한, 철도교량 단부 거동 모형시험은 동일조건으로 유한요소해석을 수행하였다. 유한요소해석에서는 레일체결장치의 거동을 선형과 비선형으로 각각 고려하였다. 시험결과에서 레일지지점 간격, 교량 받침축과 마지막 레일지지점과의 거리가 증가할수록 교대부 단부의 상향변위와 레일체결장치의 압상력이 증가하는 것으로 나타났다. 또한, 레일체결장치의 비선형 거동 특성을 고려한 유한요소해석 결과가 선형해석 결과보다 시험결과와 유사한 결과를 보여주었다.

Mechanical Reliability Calculations for the Thin Specialty Glass PV Solar Panels

This study provides important design guidance to the Photovoltaic (PV) solar panel development efforts using the finite element based computations of the PV module under the mechanical loadings. We consider specialty thin glass (Corning Eagle XG®) as superstrate of the PV module, while a standard tempered Soda-Lime-Silica Glass (SLG) is considered as bottom support. The reliability calculations for the module were performed based on the stress magnitudes obtained from the FEA computations. The PV solar panel considered in this study are supported by C-chanel rails that run along the longitudinal direction. The optimum values for the C-chanel rail support location and height were determined using FEA driven reliability calculations. A methodology involving back calculation of the limiting stresses from the reliability constraints is briefly discussed, that can save the time consuming FEA iterations and tedious post processing of FEA results thereafter to calculate reliability. Analysis shows that the best rail position is between 17% to 20% of the module width (L) from the edge. The channel located at close to L/5 from the free edges was found to give mechanical reliability of 99%. Rail height greater than or equal to 23.5 mm can be used to achieve 95% reliability for the heavy snow load test. Lower modulus encapsulants such as silicone decrease the stress on top glass Eagle EG (EXG) and increase the stress on SLG (bottom glass) to a bit over the temper stress level. The butyl perimeter seal has a minimal impact on glass stress levels.

ОБОСНОВАНИЕ ВЫБОРА РЕЛЬСОВОГО СКРЕПЛЕНИЯ ДЛЯ ТЯЖЕЛОВЕСНОГО ДВИЖЕНИЯ

Objective: To improve track maintenance, which includes the reduction of damageability and life endurance improvement of ferroconcrete rail sleepers in maintenance, elimination of factors of increased dynamic impact on sub rail support, rail fastening design for heavy haul operation, which provides for traffic safety and improvement of economic performance indicators under increased mechanical loading conditions, taking into account severe weather conditions (freeze and thaw). Methods: Service damage analysis, laboratory and benchmark tests of individual track elements and in the assembled condition. Results: Operation rate and axial load increase demands improved durability of the applied track structure components under complete passenger transportation safety control. In this case economic efficiency of the applied components is a significant factor. The research results and technical solutions, having a common purpose – to improve track maintenance under the conditions of heavy haul operation were presented in the study. The measures on elimination of factors of increased dynamic impact on sub rail support were suggested in the study: 1) application of more reliable in operation bonded-bolted joints and metal-polymer bars instead of composite ones; 2) the use of higher quality rail induction welding. The improved rail fastening design was developed for rapid curves and heavy haul operation, leading to significant increase of service life of both metal parts, due to heat strengthening of the latter, and the fastening as a whole. Practical importance: The results of the conducted research make it possible to minimize the cases of destruction of ferroconcrete sleepers and solve the issues of qualitative improvement of rail fastening components.

Чисельні дослідження умов безпеки руху поїздів з використанням математичних моделей стану залізничної колії

To date, unlike the main railways, there is no scientific justification for the norms of permissible vertical and horizontal unevenness of industrial railroad roads where traffic safety is ensured. This is especially true for industrial railway transport metallurgical enterprises that transport particularly dangerous goods (molten metal, slag, hot metal ingots). To solve this problem, mathematical models have been developed using the provisions of reliability theory, which take into account the stability of crews, fatigue strength of rails, rigidity and equivalent coefficients of rail support dissipation. Mathematical models were implemented in the Mathcad software environment. Based on the research by numerical methods, the permissible speeds of movement by irregularities of the plan and profile with different amplitudes under different operating conditions of the ways of metallurgical and mining enterprises are established. The results obtained will make it possible to provide the necessary level of traffic safety in the specific conditions of unlisted railways for the operation of special and specialized rolling stock.

Investigations on Vehicle Interaction with CWR Tracks Considering Some Aspects of Rail Support Modulus

One of the important parameters for controlling the behavior of continuous welded rail (CWR) in railway tracks is rail support modulus. Reviewing the technical literature reveals some elapsed points in this regard such as continuous or discrete supports, V-shaped rail irregularity and geometrical stiffness which can considerably affect on the vehicle-track dynamic interaction. So, the present study was allocated to numerical investigating the effects of aforementioned parameters on the vehicle-track dynamic interaction. In this matter, the finite element model of ballasted railway track in conjunction with multi-body dynamics model of vehicle was developed and they simultaneously solved numerically. This preliminary model was verified through comparison of the results with published works in this area. Consequently the model was promoted considering continuous and discrete support condition, implementing the V-shaped irregularity and geometrical stiffness. In each step, the results of the extended models were completely presented in the form track structure response.

OPTIMIZATION OF BRIDGE TRANSITION ZONES ON HIGH-SPEED RAILWAYS

[For the English abstract and full text of the article please see the attached PDF-File (English version follows Russian version)].ABSTRACT The author studies issues of track service life and rail profile stability on bridges and bridge approaches, as well as safety issues on these sections at train speeds of up to 400 km/h. The optimal control theory of dynamic processes in the bridge-track-vehicle system makes it possible to synthesize structures that exert comparatively uniform impact on the sleepers (or other rail supports) in the bridge zone while maintaining the loads on the ballast closest to their design values. Optimal designs ensure a sufficient force of the wheel-rail contact thus substantially improving traffic safety. Keywords: railway bridge, train-bridge interaction, HSR, traffic safety, track stability.

Vertical load distribution in ballasted railway tracks with steel slag and limestone ballasts

Over the last few years, use of steel slag ballast as an appropriate material instead of conventional stone ballast has gotten more attention by railway owners in various countries. In this regard, one of the technical concerns is the differences of vertical load distribution in these two materials. This factor has a significant influence on track safety and performance. In the present study, the behaviour of both kinds of ballast materials under vertical loading has been compared using a 50-meters test track including separate parts of both ballast materials. Rail support modulus and contact pressure of sleepers and ballast were obtained via a series of field tests. In order to determine the rail support modulus, the modified Talbot method has been used. The track was loaded by both light and heavy six-axle car bodies with 300 and 1350 kN weights, respectively; furthermore, a specific sleeper which was equipped by load cells was used to measure the contact pressure of sleepers and ballast under mentioned heavy car body in both types of ballast material. Results show that, with the same track superstructure and subgrade condition, the rail support modulus of test track in steel slag ballast section is 1.64 times greater than that of limestone ballast, and the compressive contact pressure of sleeper and ballast in limestone ballast was almost 1.39 times greater than steel slag ballast.

Utilization of bagasse and coconut fibers waste as fillers of sandwich composite for bridge railway sleepers

The bridge railway sleepers is an essential component in the construction of railways, as the foundation of the rail support in order to withstand the load a train that runs above it. Sleepers used in bridge construction are expected to have a longer service life, lighter weight and durable so that can be used more efficient. This research was carried out to create a model of bridges railway sleepers made of sandwich structured composite from fiber glass, epoxy resin with fillers waste of bagasse (sugar cane pulp mill) or coconut fiberboard (copra industry) that using polyurethane as an adhesive. The process of making was conditioned for small and medium industrial applications. Railway sleepers’ specifications adapted to meet the requirements of end user. The process steps in this research include; lay-up fiberglass combined with bagasse/coconut fiberboard (as fillers), gluing with epoxy resin, molded it with pressure to be solid, curing after solidification process. The specimens of composite, bagasse and coconut fiber board were tested for tensile and compressive strength. The prototype were tested of mechanical test: flexural moment test to the stand rail, flexural moment test to the middle of the sleepers and tensile strength test on one side of the sleepers, in accordance to SNI 11-3388-1994 Method testing of single block concrete sleepers and bearing single rail fastening systems. The results of mechanical testing all variations meet the technical specifications of end user such as test results for flexural moment on all prototypes, after load test, there is no visible crack. While in the tensile strength test, it seem the prototype with coconut fiberboard filler, shows better performance than bagasse fiberboard filler, the decisions is just depended on techno economic and lifetime.

An articulated assistive robot for intuitive hands-on-payload manipulation

Abstract This paper presents an intelligent assistive robot designed to help operators in lifting and moving large payloads through direct physical contact (hands-on-payload mode). The mechanical design of the robot is first presented. Although its kinematics are similar to that of a cable-suspended system, the proposed mechanism is based on articulated linkages, thereby allowing the payload to be offset from the rail support on which it is suspended. A dynamic model of the robot is then developed. It is shown that a simplified dynamic model can be obtained using geometric assumptions. Based on the simplified dynamic model, a controller is then presented that handles the physical human-robot interaction and that provides the operator with an intuitive direct control of the payload. Experimental validation on a full-scale prototype is presented in order to demonstrate the effectiveness of the proposed robot and controller.

Emission of Train-Induced Ground Vibration - Prediction of Axle-Load Spectra and its Experimental Verification

Train passages induce forces on the track, train-induced vibrations propagate through the soil and excite neighbouring buildings. The emission, which is the first part of the prediction of vibrations near railway lines, is presented by focusing on the dynamic axle loads. The calculation of the axle loads is based on the vehicle-track-soil interaction. This interaction calculus utilises the dynamic stiffness of the vehicle (the inertia of the wheelset) and the dynamic stiffness of the track-soil system. Based on various time consuming finite-element boundary-element calculations, an approximate track-soil model has been established. The vehicle-track-soil analysis yields several transfer functions between the various geometric or stiffness irregularities and the axle loads of the train. Geometric irregularities of the vehicle (the wheels) and the track (rail surface and track alignment) are the simplest components. Geometric irregularities of the subsoil (trackbed irregularities) have to be transferred to effective irregularities at rail level. The bending stiffness of the track is filtering out the short-wavelength contribution. Stiffness irregularities occur due to random variations in the ballast or the subsoil, which must also be transferred to effective track irregularities, and due to the discrete rail support on sleepers. All necessary transfer functions for the prediction of axle-load spectra are presented as general formula and as specific graphs for differing vehicle and track parameters. The prediction method is applied to a ballast track and a slab track and compared with corresponding axle-box measurements. Moreover, ground vibration measurements at numerous sites are exploited for the axle-load spectra and the validation of the prediction method. All theoretical and experimental results confirm that the dynamic axle-load spectra have an approximate value of 1 kN per third of octave and increase with train speed, track stiffness and around the vehicle-track resonance.

On effects of rail fastener failure on vehicle/track interactions

Rail support failure is inevitably subjected to track geometric deformations. Due to the randomness and evolvements of track irregularities, it is naturally a hard work to grasp the trajectories of dynamic responses of railway systems. This work studies the influence of rail fastener failure on dynamic behaviours of wheel/rail interactions and the railway tracks by jointly considering the effects of track random irregularities. The failure of rail fastener is simulated by setting the stiffness and damping of rail fasteners to be zeroes in the compiled vehicle-track coupled model. While track random irregularities will be transformed from the PSD functions using a developed probabilistic method. The novelty of this work lays on providing a method to completely reveal the possible responses of railway systems under jointly excitation of track random irregularities and rail support failure. The numerical results show that rail fastener failure has a great influence on both the wheel/rail interactions and the track vibrations if the number of rail fastener failure is over three. Besides, the full views of time-dependent amplitudes and probabilities of dynamic indices can be clearly presented against different failing status.

钢轨支承方式对地铁线路轮轨动力性能的影响

传统轨道结构中，钢轨铺设在均匀离散分布的轨枕上。钢轨支承方式不仅关系到轨道线路的建设造价，也对轨道车辆的运行安全与稳定有着重要的影响。本文基于车辆–轨道耦合动力学仿真，对钢轨连续及离散支承情形下地铁线路轮轨动力响应进行比较分析。计算结果表明，新型连续支承轨道结构上地铁车辆的轮轨力及钢轨的振动性能均优于传统的离散支承轨道。对于传统的钢轨离散支承地铁轨道，轨枕间距越小，车轮越过轨枕所引发的轮轨动态作用力和钢轨振动加速度越大。 Rails are discretely supported by uniformly distributed sleepers in traditional tracks. The rail support mode not only affects the constructing cost of metro lines, but also influences the running safety and stability of metro vehicles. This paper presents a study of the wheel/rail dynamic interactions of metro lines with continually and discretely supported rails by using vehicle-track dynamics simulations. Through numerical analysis, it is found that the innovative track with continually supported rails has advantages over the traditional track with discretely supported rails for the potentialities to reduce the dynamic wheel/rail force and the vibration level of rails. For the traditional track with discretely supported rails, a smaller sleeper span results in higher dynamics wheel/rail impact force and rail vibration acceleration due to sleeper passing excitation.

Research into parameters of energy loss when trains influence the track with wooden sleepers

The magnitude that quantitatively characterizes the process of interaction between the track and the rolling stock was determined as equivalent coefficient of dissipation (ECD). This coefficient, as an estimated magnitude, takes into account all kinds of friction forces in the process of dissipation – the forces of dry friction that depend on the deformation of the track structure, as well as viscous friction forces that depend on deformation velocity, and, possibly, other types of friction forces. These forces exert considerable effect on the characteristics of strength of a railway track and, therefore, on the safety of motion, which is why the research in this paper is quite relevant. Theoretical positions are presented that allow us to determine a mathematical formula for the calculation of ECD for rail supports of railway track. We detected the values of vertical and horizontal transverse ECD for the wooden sleepers, for which we used data of experimental studies carried out at 12 sections of Ukrainian railways with different operational conditions. Based on these data, dependence was established of ECD of rail supports in the vertical and horizontal plane on the magnitude of tonnage that passed the track. Results of the experiments indicate that with an increase in tonnage from 0 to 300 million tons, values of coefficients of dissipation in the vertical plane increase by 1.5–1.9 times, and in the horizontal plane – by about 1.3 times. Based on the aforementioned, there is a possibility of practical use of ECD to determine the current state of the track and a need for repair work.