Authored by Masoud Fathali*
Abstract
Track buckling is formation of large lateral misalignments mainly due to high compressive thermal stresses in continuous welded rail (CWR) tracks and often results in catastrophic derailments. Recognizing the actual behavior of this phenomenon requires complex interaction simulation of track components in vertical, lateral and torsional modes; however, most studies have restricted themselves to either vertical or horizontal planes, to make the analysis tractable. In the present study, the effects of track components including rails, sleepers, fastening systems and ballast materials on lateral stability of CWR tracks are determined, utilizing a developed 3D model. The validity of the model is verified through comparisons with CWERRI program results and other experimental works. Parametric studies have been conducted for both straight and curvilinear tracks. The results indicate that both parameters of ballast lateral resistance and type of rail have considerable influences on railway buckling behavior. Moreover, torsion stiffness of fastening system, type of sleeper and ballast stiffness in vertical and longitudinal directions have lower impacts.
Keywords: Buckling; Stability; CWR; Track; Superstructure; Temperature
Introduction
Continuous welded rail (CWR) is replacing jointed track for enhancing the advantages of better economics of maintenance and ride comfort. A well-known risk with CWR, however, is its potential for buckling due to high thermally induced compressive loads, with possible train derailment and track losses consequences [1]. Hence, recognition of important factors and paying attention to the effects of different parameters would be necessary in lateral stability of the tracks. Buckles are typically caused by a combination of three major factors [1,2]: high compressive forces, weakened track conditions, and vehicle loads (train dynamics). Compressive forces result from stresses induced in a constrained rail by temperatures above its “stress free” state, and from mechanical sources such as braking, rolling friction and wheel flanging on curves [3,4]. Weakened track conditions impacting the track buckling potential include reduced track resistance, lateral alignment defects, and lowered rail neutral temperature. Track resistance is the ability of the ballast, sleepers and fasteners to provide lateral and longitudinal strength to maintain track stability [5,6]. Wheel loads and train action (dynamic uplift wave) also tend to increase its size to the levels which trigger the buckling process [7,8].
Applying simple Beam, 2-D rail–sleeper models and threedimensional modeling and calculations, several researches have been accomplished for investigating the buckling behavior of CWR tracks, including primary and complementary classic methods for straight and curvilinear tracks [9-11], parametric study of thermal stability on CWR [12,13], sandwich model [14], monitoring rail road tracks [15], component materials [16], and some other scattered studies [17-19]. These models, however, have their inherent shortcomings for the CWR track buckling analysis, and most studies restrict themselves to either the vertical or the lateral plane [20]. Also, the importance of the effects of superstructure components has been less considered in comparison with the geometrical and operational conditions. Therefore, a more advanced threedimensional theoretical model for track buckling analysis is needed. The objective of this study is to develop a new, comprehensive, three dimensional CWR track model to evaluate the effects of different superstructure components including rails, sleepers, fasteners and ballast layer for a three-dimensional stability analysis. The model is developed through APDL programming code of the ANSYS software. The main advantage of this program, unlike the other numerical models, is the consideration of the whole of the track to increase the accuracy and to determine the sensitivity of different parameters. Also, for the modeling of direct part of the track at the beginning and the end of the route, the rail element itself is used instead of using the equivalent spring [18], which is more realistic. According to this model, the maximum buckling temperature through the parametric studies of track components is obtained. The validity of the present study is strictly verified through a series of comparisons with an existing theoretic model and field results.
Modeling Procedure
The developed model includes an APDL programming code in AVSYS software which accomplishes a three-dimensional analysis of track buckling with consideration of track geometrical features, mechanical properties of the components and loading conditions.
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