• Structural Monitoring and Maintenance
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• v.1 no.1
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• pp.131-157
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• 2014

Special track systems used to divert a train to other directions or other tracks are generally called 'railway turnout'. A traditional turnout system consists of steel rails, switches, crossings, steel plates, fasteners, screw spikes, timber bearers, ballast and formation. The wheel rail contact over the crossing transfer zone has a dip-like shape and can often cause detrimental impact loads on the railway track and its components. The large impact also emits disturbing noises (either impact or ground-borne noise) to railway neighbors. In a brown-field railway track where an existing aged infrastructure requires renewal or maintenance, some physical constraints and construction complexities may dominate the choice of track forms or certain components. With the difficulty to seek for high-quality timbers with dimensional stability, a methodology to replace aged timber bearers in harsh dynamic environments is to adopt an alternative material that could mimic responses and characteristics of timber in both static and dynamic loading conditions. A critical review has suggested an application of an alternative material called fibre-reinforced foamed urethane (FFU). The full-scale capacity design makes use of its comparable engineering characteristics to timber, high-impact attenuation, high damping property, and a longer service life. A field trial to investigate in-situ behaviours of a turnout grillage system using an alternative material, 'fibre-reinforced foamed urethane (FFU)' bearers, has been carried out at a complex turnout junction under heavy mixed traffics at Hornsby, New South Wales, Australia. The turnout junction was renewed using the FFU bearers altogether with new special track components. Influences of the FFU bearers on track geometry (recorded by track inspection vehicle 'AK Car'), track settlement (based on survey data), track dynamics, and acoustic characteristics have been measured. Operational train pass-by measurements have been analysed to evaluate the effectiveness of the replacement methodology. Comparative studies show that the use of FFU bearers generates higher rail and sleeper accelerations but the damping capacity of the FFU help suppress vibration transferring onto other track components. The survey data analysis suggests a small vertical settlement and negligible lateral movement of the turnout system. The static and dynamic behaviours of FFU bearers appear to equate that of natural timber but its service life is superior.

• Proceedings of the KSR Conference
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• 2007.11a
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• pp.1362-1369
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• 2007

Seoul Metro continuously converted the standard rail into continuous welded rail since the later part of 1990's, and currently, most of the sectors of the Seoul Metro are continuous welded rails. As the continuous welded rail is inhibited by the contraction and expansion force of the rail as well as rail-bed, this force is stored as the internal stress of the rail with the exception of portion of the both ends of the continuous welded rail. If the contraction and expansion of the rail is restricted, the internal stress, that is, the force in the direction of the axis, is proportional to the cross-sectional area of the rail. Therefore, with regards to the temperature changes, the internal stress changes in accordance with the type of rail, bolting apparatus, railroad tie and rail-bed. As such, the rail temperature becomes important data in securing the gap at the adjoining section of the rail in the standard rail section, and to determine the setting temperature for the continuous welded rail. In addition, it becomes basic data for maintenance of the track. Accordingly, this thesis introduces cases of installation of rail temperature detector in order to prevent and manage track defectiveness due to increase in rail temperature, and to utilize as basic data at the time of various construction and maintenance. Furthermore, this thesis aims to assist maintenance of track through systematic temperature management in the future by looking into means of its utilization.

• Structural Monitoring and Maintenance
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• v.4 no.3
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• pp.195-220
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• 2017

Nowadays, railway system plays a significant role in transportation, conveying cargo, passengers, minerals, grains, and so forth. Railway ballasted track is a conventional railway track as can be seen all over the world. Ballast, located underneath the sleepers, is the most important elements on ballasted track, which has many functions and requires routine maintenance. Ballast needs to be maintained frequently to prevent rail buckling, settlement, misalignment so that ballast has to be modelled accurately. Continuum model was introduced to model granular material and was extended in ballast. However, ballast is a heterogeneous material with highly nonlinear behaviour. Hence, ballast could not be modelled accurately in continuum model due to the discontinuities nature and material degradation of ballast. Discrete element modelling (DEM) is proposed as an alternative approach that provides insight into constitutive model, realistic particle, and contact algorithm between each particle. DEM has been studied in many recent decades. However, there are limitations due to the high computational time and memory consumption, which cause the lack of using in high range. This paper presents a review of recent ballast modelling with benefits and drawbacks. Ballast particles are illustrated either circular, circular crump, spherical, spherical crump, super-quadric, polygonal and polyhedral. Moreover, the gaps and limitations of previous studies are also summarized. The outcome of this study will help the understanding into different ballast modelling and particle. The insight information can be used to improve ballast modelling and monitoring for condition-based track maintenance.

• Structural Monitoring and Maintenance
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• v.6 no.3
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• pp.219-235
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• 2019

Scheduled inspections of common crossings are one of the main cost drivers of railway maintenance. Prognostics and health management (PHM) approach and modern monitoring means offer many possibilities in the optimization of inspections and maintenance. The present paper deals with data driven prognosis of the common crossing remaining useful life (RUL) that is based on an inertial monitoring system. The problem of scheduled inspections system for common crossings is outlined and analysed. The proposed analysis of inertial signals with the maximal overlap discrete wavelet packet transform (MODWPT) and Shannon entropy (SE) estimates enable to extract the spectral features. The relevant features for the acceleration components are selected with application of Lasso (Least absolute shrinkage and selection operator) regularization. The features are fused with time domain information about the longitudinal position of wheels impact and train velocities by multivariate regression. The fused structural health (SH) indicator has a significant correlation to the lifetime of crossing. The RUL prognosis is performed on the linear degradation stochastic model with recursive Bayesian update. Prognosis testing metrics show the promising results for common crossing inspection scheduling improvement.

• Proceedings of the KSR Conference
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• 2011.05a
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• pp.988-992
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• 2011

The buckling characteristics of the continuous welded rail track(CWR) is uncertainly varied by many influence factors, such as rail temperature, operating conditions of a train and maintenance of the track etc. Therefore, applying the probabilistic approach method is essential to rationally consider uncertainty and randomness of the various parameters that affect the track buckling. In this study, the probabilistic approach analysis was carried out and the results were compared with the deterministic approach using the buckling probability evaluation system of CWR tracks developed by our research team. From the comparison, it was identified that a probabilistic approach can quantitatively assess the reliability of the CWR tracks based on failure probability and can be used as a tool for decision making in track design, maintenance and operating etc.

• Journal of the Korean Society for Railway
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• v.11 no.3
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• pp.263-271
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• 2008

This article considers how the rail track charges of the advanced countries are performed and derived political implication to Korail. In case of North America and Japan, rail track charges are being decided to collect the infrastructure maintenance cost. In European countries, the separation of infrastructure and operation is realized and the railroad track charges are based on MC+ principle. On the other hand, Korail is paying construction cost of KTX as well as maintenance cost in Korea. As for this, railroad reform including rail track charging should be reconsidered.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.58 no.2
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• pp.308-313
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• 2009

This paper presents a reliability analysis of S-bonds for AF track circuits, which detect train movement and transmit a speed control signal to the train. Field survey shows that S-bonds are exposed to very large vibrations transferred from rail, and suffer from frequent failures when they were installed on ballasted track. We collected the time-to-failure data of S-bonds from the maintenance field of Seoul metro line 2, and made a parametric approach to estimate the statistical distribution that fits the time-to-failure data. The analysis shows that S-bonds have time-to-failure characteristics described by Weibull distribution. The estimated shape parameter of Weibull distribution is 1.1, which means the distribution has constant failure rate characteristics like exponential distribution. The reliability function, hazard function, percentiles and mean lifetime are derived for maintenance support.

• Proceedings of the KSR Conference
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• 2009.05a
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• pp.66-72
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• 2009

In order to forecast the progress of the track irregularity, we should observe the long-term track quality and divide a track into some separated divisions which have homogeneous property. For this, we define the division of track which has homogeneous property as a 'Segment' and manage the 'TQI(Track Quality Index)' using track induction data based on each segment. In this study, we introduce some methods of estimating track quality and figure out the TQIs of sample section using new FRA TQI method. In addition, we conducted a basic study of the forecasting model for the progress of track irregularity by analyzing track maintenance data.

• Structural Monitoring and Maintenance
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• v.7 no.1
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• pp.1-12
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• 2020

Railway tracks are the direct supporting structures of the trains, which are vulnerable to produce large deformation under the temperature stress or subgrade settlement. The health status of track is critical, and the track should be routinely monitored to improve safety, lower the risk of excess deformation and provide reliable maintenance strategy. In this paper, the distributed optical fiber sensor was proposed to monitor the continuous deformation of the track. In order to validate the feasibility of the monitoring method, two deformation monitoring tests on one steel rail model in laboratory and on one real railway tack in outdoor were conducted respectively. In the model test, the working conditions of simply supported beam and continuous beam in the rail model under several concentrated loads were set to simulate different stress conditions of the real rail, respectively. In order to evaluate the monitoring accuracy, one distributed optical fiber sensor and one fiber Bragg grating (FBG) sensor were installed on the lower surface of the rail model, the strain measured by FBG sensor and the strain calculated from FEA were taken as measurement references. The model test results show that the strain measured by distributed optical fiber sensor has a good agreement with those measured by FBG sensor and FEA. In the outdoor test, the real track suffered from displacement and temperature loads. The distributed optical fiber sensor installed on the rail can monitor the corresponding strain and temperature with a good accuracy.

• Journal of the Korean Society for Railway
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• v.12 no.1
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• pp.167-174
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• 2009

Due to the travelling of the train with high speed the period of maintenance activities of the ballasted track is coming to be short, and more from the residential area of the ballasted track tunnel circumference the civil appeal is increasing with railroad vibration problem. To reduce the vibration problem and a maintenance cost establishes the ballast mat in the tunnel within part segment. In this study, to estimate the vibration reduction effect of the ballast mat we have done a comparative analysis with the vibration field test by the transit train by at the ballasted track with ballast mat and the standard ballasted track without vibration protection in tunnel.