Kot recently completed a project to install track on a railroad line connecting two Brazilian states. In this article, you can learn more about this Succes story by the company’s team!
Introduction
First, railroad derailments are serious incidents that must be prevented because, in addition to causing property damage and service disruptions, they can result in fatal accidents. In this regard, the main factors to watch for are increased load on the wheel flange, decreased vertical load, and an increased wheel angle of attack. [1]
In addition, one method for evaluating derailments was proposed by Nadal, which correlates the lateral and vertical load values (L/V). When this coefficient exceeds the Nadal limit, the wheel flange shifts upward on the rail, causing a derailment. [2]
Figure 1 shows the derailment mechanism in which Nadal's condition applies.
Figure 1: Derailment mechanism. [1]
Computer model
Previously, in another study also conducted by Kot, the rail, sleeper, and ballast assembly was modeled computationally, 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]
Subsequently, 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 the eccentricity of the vertical load relative to the rail centerline.
In addition, extensometry—the method used in this study—is employed to evaluate surface deformations in materials. If you’d like to learn more about the application of extensometers, check out the articles on the Kot blog:
Instrumentation proposed by Kot
The methodology proposed by Kot for conducting the field tests is described below:
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- First, to evaluate the vertical load, extensometers were installed on both sides of the rail web, spaced at regular intervals and aligned with the ties immediately below. This made it possible to measure both the lateral and vertical loads. The lateral loads were calibrated using a hydraulic cylinder. Next, the influence of the vertical load on the lateral load region was evaluated, as shown in Figure 4.
Figure 4: Evaluation of the influence of the vertical load on the lateral load region. [3]
Subsequently, strategic sections of the track were instrumented based on the history of previous failures. Measurements were taken using extensometers to record deformations and LVDTs (linear variable displacement transducers) to measure the vertical displacement of the ties for subsequent evaluation of the ballast stiffness. Some images of the fieldwork 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
After the tests were conducted, the numerical results obtained were compared with those generated by the Chevron method through computer simulation. As a result, these numerical analyses made it possible to evaluate the effects of the vertical load eccentricity parameters and lateral load values. However, both methods required calibration to accurately evaluate the deformations.
On the other hand, the advantages of the method proposed by Kot lie in its ability to retrieve the desired data in cases of vandalism, cable breaks, and other failures. In addition, the methodology requires less time for instrumentation, since it uses fewer sensors than Chevron had anticipated.
Conclusion
In short, the method suggested by the Kot team offers advantages over the conventional methodology, as it facilitates a more reliable study by analyzing and comparing data from experimental tests with the theoretical computational model. Furthermore, the implementation takes less time, making the study even more beneficial for companies.
Finally, it is worth noting that Kot has extensive expertise in this field, having implemented solutions at hundreds of assets, enabling it to assess different operational 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.
