عنوان مقاله [English]
Although the current analysis and design of railway track systems are based on the assumption of continuous and linear behavior of the rail support system, repair and maintenance plans have considerable influences on the structural behavior of the track support system, particularly after accumulative loading or track tamping. Recent experimental investigation indicated the behavior of the track support system is time and stress dependent. The amount of traffic passed and the quality and quantity of maintenance activities can considerably influence the track response functions. Although some experimental investigations have been carried out to study the time and stress dependent characteristics of the ballast and subgrade materials, the effects of the consideration of these characteristics on the track analysis and design, need further evaluations. Furthermore, the recent extensive increases in axle loads, speed and traffic volumes in rail transport systems, require more precise analytical and mechanistic approaches for railway track system. This research is a response to this need. In this paper, the current practices in the analysis and design of railway track system are discussed. A mode of track support system with consideration of discrete supports is developed. By comparison of the analyses results obtained from track models with continuous and discrete support systems, the accuracy of the assumption made in the Winkler model, used in the current design approach, are evaluated. The nonlinear behaviors of the track support system were studied and the influences made by the consideration of the non-linearity of the track support system on the rail design criteria were investigated. Rail bending moments and rail deflections as the main rail design criteria are obtained form track with a linear support and nonlinear behaviors. Obtaining large discrepancies between the results obtained from linear and non-linear analyses, the importance of the track regular and systematic repairs, in particular tamping and stabilizing the ballast, are proved. It is shown that the consideration of regular repairs of the track support system improves the long term reliability and accuracy of the current track design approach. Recommendations are made on the track maintenance and repairs in order to keep the track support system in the linear conditions.