Modeling and Analysis of Rail Pad Stiffness on Ballasted Railway Track

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Addis Ababa University


Railway infrastructure, has become the most competitive transport means due to its unique advantages (efficiency, transportation capacity, low environmental impact, etc). Rail pad is the regularly used resilient element, and is very crucial as it act as a softening medium between rail and sleeper. A soft rail pad permits a larger rail deflection which lead to the fatigue of this component or others like the fastener system but allows the axle load from the train to spread over more sleepers/ties. In contrast, stiff pads cause larger dynamic actions on the infrastructure components such as sleeper and ballast material. Low stiffness rail pads of less than 100 kN/mm have been recommended in a number literature implying a potential neglect of associated problems of excessive rail displacement caused by very soft rail pads. This is the basis for motivation of this study to analyze the effects of rail pad stiffness on ballasted railway track so as to recommend rail pad stiffness that contributes towards minimal rail displacement and sleeper acceleration. A 3D numerical model was established using ABAQUS/CAE 6.14 to carry out the investigation. The FEA model entails a rolling wheel, UIC 54 rail, rail pads, concrete sleepers, ballast and subgrade. The prepared model was verified with a laboratory experiment that replicated a ballasted track section (from one reference paper [1]). The basic parameters used in the model were synonymous to that of the experimental test and was in compliance with literature and the different standards such AS1085.14, AREMA and other acknowledged publications. Track behavior was noted in the form of stress, displacement, acceleration and corresponding rail seat loads to categorize the stiffness of the rail pad, that limits the negative extremes in track behavior. Parametric studies were executed with various rail pad stiffness to understand their consequence on the behavior of track components; rail and sleeper. This study showed that, with increase in rail pad stiffness at 200 and 300 kN/mm rail pad stiffness, the rail vertical displacement decreases by at least 64-73% and 79-83%, rail vertical acceleration decreases by 37-56% and 56-77%, while rail vertical stress increased by 44-57% and 68-73%, the rail seat loads increased by 52-56% and 68-74% under static loading and increased by 37% and 55% under dynamic loading, the sleeper vertical acceleration increased by 55% and 62%. Due to correlation behavior of most of the out puts with increasing stiffness of rail pads, rail vertical displacement and sleeper vertical acceleration were chosen as the two criteria for selecting the most suitable rail pad stiffness. Even though some researchers recommend soft rail pads below 100 kN/mm rail pad stiffness, which could increase rail movements and deflection, this research study has recommended rail pad stiffness of 150 kN/mm with 48% reduction in rail displacement and 44% increase in sleeper acceleration. This is also in an agreement with recommendation of Nazmul Hasan (2019) [2], that the softest rail pad should not be less than 100 kN/mm and desired range is 116-256 kN/mm.



Modeling, Analysis, Ballasted track, Rail pad, Stiffness