Elastic characteristics of the underrail base of a ballastless railway track

Objective: Experimental determination track modulus and the coeffi cient of relative stiffness of underrail base and the rail, which are the main elastic characteristics that determine the stresses in the structural elements of track superstructure under the impact force from the train. The values of these parameters for a track with a ballast layer are well studied, in contrast to a ballastless track. Comparison of the elastic characteristics of a ballastless railway track with analogs of a track on ballast, as well as an assessment of their effect on the stress-strain state of the superstructure elements of a ballastless track. Methods: When carrying out full-scale tests, strain-gauge methods for measuring stresses in the elements of the track superstructure were used. The obtained values were processed by the methods of mathematical statistics. One statistical series included the values of stresses corresponding to one type of rolling stock, fi xed axle load and train speed, changing by no more than 10 km/h. The probability level in processing the results was taken in all cases equal to 0,994. Results: The values of track modulus and the coeffi cient of the relative stiffness of the underrail base and the rail were obtained for a ballastless structure of the RHEDA 2000 type. Practical importance: The results allow us to consider the rail as a beam lying on a solid elastic foundation in relation to the ballastless track and use the existing calculation methods for the design of ballastless track structures depending on the operating conditions.

Modelling the Effect of Track Stiffness Variation on Wheel Rail Interaction Using Finite Element Method

For predictive maintenance purpose, wheel and rail wear evolution models have been developed based on wheel rail contact force calculations. These models are known to assume the wheel rotating on a rigid rail. However recent developments have shown that the flexibility of the track plays an important role in wear evolution. On the other hand, vertical track stiffness variation along the track is known to exist and to affect the track flexibility. The present research work investigates the influence of non-uniform track modulus on the wheel rail contact forces using elasto-plastic explicit dynamic Finite Elements (FE). The FE model is composed of a quarter car model running on a rail supported by three cross-ties. The modulus of elasticity of the cross-ties is calibrated to produce the total track modulus of the railroad track infrastructure. Non-uniformity of the track is modeled by assigning distinct elasticity moduli to the cross-ties. The instantaneous contact physical parameters are extracted from FE models repetitively for various cross-tie modulus ratios. The results show that increase in cross-tie modulus variation results in increased fluctuation amplitudes of wheel-rail contact parameters such as force, stress and contact area. This effect leads to changes of the rate of material removal on the wheels and rails. This research work intends to incorporate the spatial variation of the railroad track stiffness into rail vehicle wheel and track wear prediction models.

Track Modulus Assessment of Engineered Interspersed Concrete Sleepers in Ballasted Track

Ballasted railway track is typically constructed using sleepers that are manufactured from a common material type within a given length of track. Timber and concrete are the two most common sleeper materials used internationally. Evidence from historical installations of interspersed concrete sleepers in timber sleeper track in North America has indicated inadequate performance, due largely to the heterogeneity in stiffnesses among sleepers. Theoretical calculations reveal that interspersed installation, assuming rigid concrete sleepers and supports, can result in rail seat forces more than five times as large as the force supported by the adjacent timber sleepers. Recently, engineered interspersed concrete (EIC) sleepers were developed using an optimized design and additional layers of resiliency to replace timber sleepers that have reached the end of their service lives while maintaining sleeper-to-sleeper stiffness homogeneity. To confirm that the concrete sleepers can successfully replicate the stiffness properties of the timber sleepers installed in track, field instrumentation was installed under revenue-service train operations on a North American commuter rail transit agency to measure the wheel–rail vertical loads and track displacement. The results indicated that there are minimal differences in median track displacements between timber (2.26 mm, 0.089 in.) and EIC sleepers (2.21 mm, 0.087 in). Using wheel-load data and the corresponding track displacements associated with each wheel load, track modulus values were calculated using the single-point load method based on beam on elastic foundation (BOEF) fundamentals. The calculated values for the track modulus indicated similar performances between the two sleeper types, with median values of 12.95 N/mm/mm (1878 lbs./in./in.) and 12.79 N/mm/mm (1855 lbs./in./in.) for timber sleepers and EIC sleepers, respectively. The field results confirmed the suitability of the new EIC sleeper design in maintaining a consistent track modulus for the location studied, thus evenly sharing loads between and among sleepers manufactured from both concrete and timber.

Continuous Evaluation of Track Modulus from a Moving Railcar Using ANN-Based Techniques

Track foundation stiffness (also referred as the track modulus) is one of the main parameters that affect the track performance, and thus, quantifying its magnitudes and variations along the track is widely accepted as a method for evaluating the track condition. In recent decades, the train-mounted vertical track deflection measurement system developed at the University of Nebraska–Lincoln (known as the MRail system) appears as a promising tool to assess track structures over long distances. Numerical methods with different levels of complexity have been proposed to simulate the MRail deflection measurements. These simulations facilitated the investigation and quantification of the relationship between the vertical deflections and the track modulus. In our previous study, finite element models (FEMs) with a stochastically varying track modulus were used for the simulation of the deflection measurements, and the relationships between the statistical properties of the track modulus and deflections were quantified over different track section lengths using curve-fitting approaches. The shortcoming is that decreasing the track section length resulted in a lower accuracy of estimations. In this study, the datasets from the same FEMs are used for the investigations, and the relationship between the measured deflection and track modulus averages and standard deviations are quantified using artificial neural networks (ANNs). Different approaches available for training the ANNs using FEM datasets are discussed. It is shown that the estimation accuracy can be significantly increased by using ANNs, especially when the estimations of track modulus and its variations are required over short track section lengths, ANNs result in more accurate estimations compared to the use of equations from curve-fitting approaches. Results also show that ANNs are effective for the estimations of track modulus even when the noisy datasets are used for training the ANNs.

Estimation of vertical bending stress in rails using train-mounted vertical track deflection measurement systems

This paper presents a new methodology for the estimation of bending stresses over long sections of rails from the vertical track deflections measured using train-mounted instrumentation. The basis of this method is to apply mathematical correlations between the rail deflections and stresses to interpret the deflection measurements. A new finite element modeling method was developed to investigate mathematical correlations between the rail deflections and stresses for different ranges of track modulus. The stochastic nature of the track modulus, as one of the dominant factors influencing rail deflections and stresses, was simulated. The rail responses to applied loads were then calculated and compared for scenarios of constant and variable track modulus values. The study resulted in a detailed framework that can be employed to estimate rail bending stresses from train-mounted vertical track deflection measurements. This framework allows the estimation of the probability distributions of maximum tensile and compressive bending stresses in the rail head and base, which are necessary for calculating the rail reliability under applied loading.