Track Modulus: Ballasted and Direct Fixation Track

2019 ◽  
Author(s):  
Nazmul Hasan
Keyword(s):  
Track Modulus

Track modulus detection by vehicle scanning method

2020 ◽  
Vol 231 (7) ◽  
pp. 2955-2978 ◽  
Author(s):  
Y. B. Yang ◽  
Z. L. Wang ◽  
B. Q. Wang ◽  
H. Xu
Keyword(s):  
Scanning Method ◽  
Track Modulus

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

Vibration ◽  
2020 ◽  
Vol 3 (2) ◽  
pp. 149-161 ◽  
Author(s):  
Ngoan T. Do ◽  
Mustafa Gül ◽  
Saeideh Fallah Nafari
Keyword(s):  
Curve Fitting ◽  
Estimation Accuracy ◽  
Promising Tool ◽  
Lower Accuracy ◽  
Track Condition ◽  
University Of Nebraska Lincoln ◽  
The University ◽  
The Relationship ◽  
Track Modulus ◽  
Different Levels

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.

Effects of Different Models on Natural Frequencies of Short Span Bridges Used in High Speed Rail

2015 ◽  
Author(s):  
Said I. Nour ◽  
Mohsen A. Issa
Keyword(s):  
Timoshenko Beam ◽  
High Speed ◽  
Natural Frequencies ◽  
Bernoulli Beam ◽  
High Speed Rail ◽  
Vertical Stiffness ◽  
Short Span ◽  
Elastically Supported ◽  
Euler Bernoulli Beam ◽  
Track Modulus

The natural frequencies of vibration of short span bridges used in high-speed rail were investigated. Three different models of increasing complexity were evaluated and their effects on the vibration frequency were compared to the first basic model of simply supported Euler-Bernoulli beam. In the second and third cases, the bridge was modeled as an Euler-Bernoulli and Timoshenko beam supported at its two ends by identical spring elements with an equivalent vertical stiffness to simulate elastomeric bearings and soil foundation. The boundary value problem was solved numerically to extract the bridge eigenfrequencies. In the case of Euler-Bernoulli beam, curve fitting techniques were used to deduce accurate simple empirical formulae to calculate the first six natural frequencies of an elastically supported bridge. In the case of a Timoshenko beam, graphical solutions were proposed to compute the fundamental frequency. Results confirmed that the use of Timoshenko beam theory reduces the natural frequency and the consideration of flexible supports further decreases the natural frequency. In the fourth model, the interaction of the track and the bridge was included. The bridge was modeled as an elastically supported beam and the track was modeled as a spring-damper element with an equivalent vertical stiffness resulting from track components like rail pads, cross-ties and ballast. A parametric study was performed to analyze the effects of the track stiffness on the natural frequencies of the bridge. Graphical solutions were presented to quantify the change of the normalized natural frequencies of the system with the increase in the track modulus. Results indicated that the changes in the track modulus have no significant effects in models with rigid supports. A decrease in the fundamental frequency was noticeable with softer track modulus as the support flexibility increased.

scholarly journals In-Situ Test Measurement Techniques Within Railway Track Structures

2008 ◽  
Author(s):  
Justin S. Anderson ◽  
Jerry G. Rose
Keyword(s):  
Measurement Techniques ◽  
Earth Pressure ◽  
High Volume ◽  
Distribution Patterns ◽  
Railway Track ◽  
Track Structure ◽  
Film Sensor ◽  
Pressure Distributions ◽  
Axle Loads ◽  
Track Modulus

Recent changes in national transportation needs have placed increased burden on railroad infrastructure. To meet the increased demand for efficient freight transport, the railroad industry has increased traffic volume and maximized axle loadings. Increased axle loads have forced railroads to reevaluate existing infrastructure to ensure their ability to accommodate the additional traffic loads. It is imperative to design and maintain tracks such that they can withstand high volume and increasing axle loads over an extended service life, considering the track structure is the most significant capital expense for railroad companies. It has been desirable for years to develop non-intrusive procedures to directly measure pressures and stresses at various levels and interfaces in the railroad track structure in order to optimize track designs and improve subsequent track performance. Methods for measuring both pressures and deflections have been presented in recent research focusing on assessing the performance of trackbeds with increased track modulus, primarily through the addition of asphalt underlayment. These studies involve instrumenting HMA trackbeds with earth pressure cells and displacement transducers to measure pressure levels and distributions within the track structure and rail deflections under moving trains. Additional test methodologies have been developed to include pressure readings at interfaces like the rail/tieplate interface and the tieplate/tie interface using very thin pressure sensitive Tekscan sensors. The Tekscan Measurement System uses a piezoelectric film sensor composed of a matrix-based array of force sensitive cells, similar to mini strain gauges, to obtain accurate pressure distributions between two surfaces in the track. The procedure appears applicable for a wide variety of specific track related measurements to include: 1) analyzing pressure distribution patterns at the rail base/tie plate/tie interfaces to minimize wear and eliminate pressure points, 2) validating and optimizing horizontal curve geometric design criteria relative to superelevation, 3) assessing crossing diamond, other special trackwork, and bridge approach impact pressures, and 4) evaluating the advantages/disadvantages of various types of tie plates, fastenings, and tie compositions with the objective of equalizing pressure distributions over the interface areas. Results of testing are presented in detail for test installations on CSX Transportation heavy tonnage mainlines and at the Transportation Technology Center (Pueblo) low track modulus heavy tonnage test track.

scholarly journals Track Modulus Assessment of Engineered Interspersed Concrete Sleepers in Ballasted Track

2020 ◽  
Vol 11 (1) ◽  
pp. 261
Author(s):  
Arthur de Oliveira Lima ◽  
Marcus S. Dersch ◽  
Jaeik Lee ◽  
J. Riley Edwards
Keyword(s):  
Theoretical Calculations ◽  
Single Point ◽  
Point Load ◽  
Railway Track ◽  
Optimized Design ◽  
Wheel Load ◽  
Field Instrumentation ◽  
Stiffness Properties ◽  
Materials Used ◽  
Track Modulus

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.

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

2021 ◽  
Author(s):  
Lovejoy Mutswatiwa ◽  
Celestin Nkundineza ◽  
Mehmet A. Güler
Keyword(s):  
Prediction Models ◽  
Research Work ◽  
Contact Forces ◽  
Physical Parameters ◽  
Fe Model ◽  
Railroad Track ◽  
Track Stiffness ◽  
Stiffness Variation ◽  
The Cross ◽  
Track Modulus

Abstract 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.

Direct Fixation Fastener (DFF) Spacing and Stiffness Design

2011 ◽  
Author(s):  
Nazmul Hasan
Keyword(s):  
Natural Frequency ◽  
Frequency Ratio ◽  
Vibration Isolation ◽  
Design Procedure ◽  
Past Performance ◽  
Spring Rate ◽  
Exciting Frequency ◽  
Noise Vibration ◽  
Mass Spring ◽  
Track Modulus

Direct fixation fasteners are one of the most important elements in trackwork design. Elastomeric pads are incorporated in the fastener to provide vertical and horizontal flex and they assist in the reduction of noise, vibration and impact. The spring rate in DFF is often adjusted to mitigate ground borne vibration, that adjustment then affects the track modulus. Currently no industry-wide specifications exist for the design, definition or procurement of direct fixation fasteners. A thorough examination of the characteristics and past performance of available fasteners, as well as the characteristics of the proposed transit vehicle should be undertaken prior to fastener selection for any specific application. In this paper a procedure is suggested to calculate the spacing and desirable (vertical) stiffness of DFF that would mitigate noise, vibration and impact. There are two issues to consider enabling proper vibration isolation. The dominant issue is spring rate and the secondary issue is damping constant. Both are considered. Rail can be defined as a beam supported by DFF, directly fixed to a concrete slab. Usually light mass-spring ballast less track systems have a natural frequency varying from 12 Hz up to 18 Hz. Firstly a natural frequency for the direct Fixation Track is chosen. This choice must conform to the fact that exciting frequency such as train passing frequency should not go close to the natural frequency level so as to avoid resonance. Using a load-deflection formula for the track, a formula for natural frequency of a mass-spring system, a DFF passing frequency formula and relation between track modulus and characteristic length, DFF stiffness can be calculated. The design of stiffness and spacing of DFF does not lead to a unique value. There will always be a range of value depending on the choice of frequency ratio, r. It is found that spacing and stiffness are strongly correlated with R2 = 0.991. At the end a discussion follows on how to choose the value of natural frequency, fn stiffness amplification factor, R and the frequency ratio, r. Finally an application of the proposed design procedure is shown.

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