چكيده به لاتين
Due to an increasing trend in higher axle loads and operational speeds, employing numerical models for estimation of dynamic response of track and a reliable estimate of forces in superstructure elements are of great importance. In cases with short wave-length irregularities or rail discontinuities such as corrugations, rail joints and broken rails, contact-impact forces will be generated due to wheel passing over these irregularities. So, common wheel-rail contact theories are not applicable and it’s important to consider contact-impact forces in numerical models. A3D finite element model using Abaqus FE package has been employed in this study to investigate the effect of train and track characteristics on contact-impact forces in the vicinity of rail breakage as well as dynamic forces at railpad and ballast which are important elements in track's superstructure, and constitute largely to the costs of track maintenance. Numerical model has been verified by results of field test carried out by passing over a rail discontinuity which has been made by separating fish plates at a rail joint. It has been shown that numerical results have an acceptable agreement with experimental results. The effect of some train and track parameters and broken rail condition such as train speed, gap length, axle load, railpad and ballast characteristics, non-linear behavior of materials, rail breakage location, temporary repair of broken rail and sleeper spacing on track forces has been investigated by numerical model. Results suggest that increasing train speed from 60 km/h to 110 km/h would increase dynamic impact factor from 2.46 to 4.11. Increasing axle load results in an increase in impact forces between rail and wheel and forces in railpad and ballast, while dynamic impact factor is reduced. Investigating of track parameters effect demonstrate that ballast stiffness is most important characteristic of track which has a reverse effect on dynamic impact forces. It is concluded that for pads-particularly soft pads-linear model estimates forces that are comparably less than those estimated by non-linear model. Moreover decreasing unloading length and consequently derailment risk of train could be occurred by decreasing of sleeper spacing, locating of rail breakage at the middle of two adjacent sleepers and temporary repair of broken rail.