draw cross section of railways track and write down funtion of their component?
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Explanation:
Context 1
... track is a multi-component mechanical structure that is loaded by passing trains. The loading is stochastic due to different train types with different speeds, axle loads and wheel tread surface conditions. One component in the railway track is the sleeper. Its two main purposes are to distribute the load from the train to the underlying ballast and to maintain the gauge between the rails. In Sweden, the most common sleeper type is the prestressed concrete monoblock. This sleeper type is the focus of this work. A simplified cross- section of a railway track is illustrated in figure 1. In current design of sleepers it is common to follow guidelines; two examples are the European standard [1] and a UIC leaflet [2]. All such guidelines refer to the minimum allowable capacity of the bending moments at three locations along the sleeper. These are at the rail seats, i.e. under the rails, and at the centre of the sleeper. This is motivated by field studies in which it is noted that transverse cracks are most common on the bottom surface at the rail seat areas and on the top surface at the centre section. In analysis of sleeper capacity, it is therefore the crack-opening tensile stresses at these locations that are of interest. Discrete wheel tread defects over a small section of the wheel tread may generate severe impact loads in the wheel-rail contact for each wheel revolution. One of the most common discrete tread defects, the wheel flat, is developed due to unintentional sliding (without rolling) of the wheel along the rail. The reason for the sliding may be that the brakes are poorly adjusted, frozen or defective, or that the braking force is too high in relation to the available wheel/rail friction [3]. In spite of the occurrence of impact loads, such as those due to wheel flats, the sleeper design guidelines are based on static analyses. A nominal static wheel load is multiplied with a dynamic magnification factor. The value of this factor differs between design guidelines and it is not clear how these values are justified by observations in the field. Since the frequency content and the magnitude of the prescribed load have an influence on the sleeper response, the dynamics of the track (including the sleeper) is accounted for in this study. Another difference between different sleeper design guidelines is how the influence of the ballast support is accounted for. That is, how the ballast stiffness is distributed along the sleeper and how the ballast pressure on the sleeper is developed from that. The traffic on Swedish railways moves towards higher speeds for passenger trains and heavier loadings of the freight trains. According to the existing sleeper design guidelines, this requires an increase of the bending stiffness. However, there is a lack of knowledge about the in-situ loading conditions for sleepers and the design guidelines can therefore be questioned. Other design methods, such as probabilistic design with proper data statistics, could be an alternative. The purpose of this paper is to investigate the possibility of using metamodelling techniques in the application of probabilistic design of railway sleepers. That is, can a metamodel together with Monte Carlo simulation predict an accurate probability of failure for different sleeper designs? Of interest is also the computational time required to obtain an accurate estimation of the ...