Kot carried out instrumentation work on the tracks of a railroad that connects two Brazilian states. In this article you can find out more about this Succes story developed by the company's team!
Introduction
Derailments on railroad tracks are serious occurrences that must be prevented because, in addition to causing material losses and track disruptions, they can lead to fatal accidents. In these cases, the main points to look out for are the increased load on the wheel flange, the decrease in vertical load and the increase in the angle of attack of the wheels. [1]
One of the methods for assessing derailments was proposed by Nadal, who correlates the lateral and vertical load values (L/V). When this coefficient exceeds Nadal's limit, there is a displacement from bottom to top of the wheel flange on the rail, causing derailment. [2]
Figure 1 shows the derailment mechanism in which Nadal's condition applies.
Figure 1: Derailment mechanism. [1]
Computer model
In a previous work, also developed by Kot, the rail, sleeper and ballast set was computationally modeled, as shown in Figures 2 and 3.
Figure 2: Three-dimensional model of the assembly. [3]
Figure 3: Overview of the three-dimensional model of the assembly. [3]
Vertical loads were applied to the model at three different contact points on the sleeper and at three contact points in the region between sleepers, assuming eccentricity of the vertical load in relation to the center line of the rail.
Extensometry, the method applied in this study, is used to evaluate the surface deformations of materials. To learn more about the application of strain gauges, check out the articles on Kot's blog:
Instrumentation proposed by Kot
The methodology proposed by Kot for carrying out the field tests is described below:
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- To assess the vertical load, strain gauges were installed on both sides of the rail core, at intervals and aligned with the sleepers immediately below. This made it possible to collect both lateral and vertical loads. The lateral loads were calibrated using a hydraulic cylinder. The influence of the vertical load on the lateral load region was then evaluated, as shown in Figure 4.
Figure 4: Evaluation of the influence of the vertical load on the lateral load region. [3]
Strategic areas of the track were instrumented, based on the history of previous failures. Measurements were made with strain gauges to collect deformations and also with an LVDT (linear variable displacement transducer) to measure the vertical displacement of the sleeper for later assessment of the ballast's stiffness. Some images of the field work can be seen in Figures 5, 6 and 7.
Figure 5: Extensometers attached to the rail core. [3]
Figure 6: Extensometers attached to the rail core. [3]
Figure 7: Calibration of the lateral load on the track. [3]
Results
The numerical results obtained were compared with those generated by the Chevron method by means of computer simulation. These numerical analyses made it possible to evaluate the effects of the vertical load eccentricity parameters and lateral load values. Both methods required calibration in order to correctly assess the deformations.
The advantages of the method proposed by Kot are that it makes it possible to obtain the desired data in cases of vandalism, cable breakage and other errors. In addition, the methodology has a shorter instrumentation time, since it uses fewer sensors than that provided by Chevron.
Conclusion
The method suggested by the Kot team has advantages when compared to the conventional methodology, as it favors the development of the study in a more reliable way due to the analysis and comparison of experimental test data and the theoretical computer model. In addition, the instrumentation is carried out over a shorter period of time, making the study even more advantageous for companies.
It should be noted that Kot has a great deal of know-how in the area, having instrumented hundreds of assets, being able to assess different operating contexts and contribute to its clients' results. Contact our team for more information!
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References
[1] GWALIOR, MAHARAJPUR, A Technical Guide on Derailments, CAMTECH/M/3, April 1998
[2] B. MARQUIS & R. GREIF, "Application of Nadal Limit in The Prediction Of Wheel Climb Derailment", in Joint Rail Conference, [S.I], 2011.
[3] Kot Engenharia archive.
