Center for Railway Engineering

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Browsing Center for Railway Engineering by Subject "acceleration"

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    Analysis of Railway Track Stiffness Variation and Its Influence
    (AAU, 2015-10) Abreham, Demissie; Mequanent, Mulugeta (Mr.)
    Railway track stiffness is a basic parameter of track design which influences the bearing capacity and the dynamic behavior of passing vehicles. In particular, track geometry quality and the life of track components. The stiffness definition must include inelastic and non-linear behavior of the supper structure and substructure elements as well as the existence of the stiffness under dynamic load. In most case track stiffness is a function of track superstructure and substructure material properties. In this paper the influence of track component stiffness variation by using time and frequency domain of FEM (ABAQUS software) analyzed and discussed on the results observed. The Modeling analysis of track stiffness variation depends on the track component (rail-pads, sleeper, ballast and subgrade) stiffness variation and the Results for each track component stiffness variations. Interactive forces, track component displacements, Velocities and acceleration were presented. The analysis consider the influence of rail-pad stiffness, ballast stiffness, sleeper spacing, train speed and subgrade material on track structures. During operation and moving of the freight trains falling of small particles over the ballast layer causes an increase of stiffness in the layer of ballast and gradual deterioration of ballast effect on size of ballast grade and forming powder due to friction exists between stones rubbing together, which reduce the stiffness of ballast. Using the software ABAQUS found that, decrease in sleeper spacing and increases in ballast young’s modulus, ballast depth, sub grade young’s modulus and rail moment of inertia increases the track stiffness at all. In general, relatively high track stiffness is beneficial as it provides sufficient track resistance to applied loads and results in decreased track deflection, which reduces track deterioration. On the other hand, very high track stiffness leads to increased dynamic forces in the wheel rail interfaces as well as on the sleepers and ballast which can cause wear and fatigue of track components.
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    The dynamic effect of rail joint on Railway Track components
    (AAU, 2017-06) Abraham, Girma; Mathias, Kabtamu (Mr.)
    A rail irregularity is the weakest link in the railway track which highly creates the impact forces. The impact forces in the rail irregularity such as insulated rail joints or bolted rail joints can be extremely large and can cause serious failures in the track structure, which can lead to a significant economic loss for track owners by making damage to rails and to the sleepers beneath. The main question that to be answered in relation to the imperfection or rail irregularity especially with the bolted jointed rail is that; “what is the dynamic effect of this weakest point or jointed rail on the railway track components”. Thus, this paper is mainly focuses on the studying this effect. In analyzing this effect, the finite element modeling software, ABAQUS having 2D model algorithm is used to analyze the dynamic effect of the jointed rail on the track system response. In doing this, four different vehicle speeds ranges from 60Km/hr to 200Km/hr are used for analyzing the dynamic effect of jointed rail on the railway track components. The results show that; as the vehicle speeds of the train increases from 60Km/hr to 200Km/hr, the spatial displacement of the rail, sleeper and ballast is also increases in zigzag forms for the entire length of the rail. Apart from this, to further studying the dynamic effect of the jointed rail on the track components different type of rail pads having a stiffness of 50MN/m, 100MN/m, 150MN/m, 200MN/m and 500MN/m area also included in the study to account the dynamic effect of the rail pads on the track performance. The results this thesis indicates that; the rail pads stiffness has significant role in reducing the vertical vibration of the rail, sleeper and ballast. Moreover, in order to further analyze the dynamic effect of the jointed rail on the railway track components; the effect of the position of sleepers, wheel load and diameters are also presented. In line with this, with all the above scenarios, the results show that as the vehicle speed of the wheel, wheel diameters and number of the wheels increases, the dynamic acceleration and spatial displacement of the rail, sleeper and ballast especially at and around the rail joints are also increases. Further, the dynamic actions such as frequency analysis, acceleration and dynamic spatial displacement are also determined at and around the jointed rail. Thus, the vertical vibration of the rail and sleeper is maximum at the frequency range from 90Hz to 130Hz and the vertical vibration of the ballast is maximum at the frequency range from 174Hz to 300Hz.