الفهرس 
Thesis objectives
STRUCTURAL RESPONSE OF PRESTRESSED MONOBLOCK CONCRETE SLEEPERS AND FASTENING SYSTEMS AT RAIL SEATOnly 14 pages are availabe for public view
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Abstract
According to the field and numerical measurements, the railway tracks are inevitably exposed at horizontal curves to coinciding vertical and lateral loads, which in some cases could be of high intensity. Nonetheless, the behaviour of concrete sleepers has been considered by the international design standards that it is predominantly influenced by the magnitude of vertical load. This is concurrent with the previous investigations which have not shown how lateral loads could influence the sleeper behaviour considering the effects of fastening system components. As a response, this research aims to investigate the extent to which concrete sleepers and fastening systems are influenced by coupling vertical and lateral loads formed at horizontal curves of railway tracks.
To address these issues, three-dimensional finite element models were accomplished and rigorously verified against analytical, numerical, and experimental studies existing in the literature. The first stage of this study includes a comprehensive structural analysis of the local response of concrete sleepers and fastening systems at rail seats under varied lateral loadings as well as the global distribution of vertical and lateral wheel loads on railway track components. Different designs of concrete sleepers and fastening systems were considered in the study to cover the existing fastening systems categories including ‘‘screwed clip systems’’ and ‘‘embedded clip systems’’. Included in this stage also is a discussion of the influences of different parameters such as the sleeper spacing, elastic modulus of the rail pad, lateral friction coefficient at sleeper-rail pad interface, and lateral to vertical loading ratio. The interaction influence between these parameters was also thoroughly analysed to provide more comprehensive results.
Among the studied parameters, the outcomes of the finite element models showed that the elastic modulus of the rail pad and the lateral coefficient of friction are the most critical parameters that influence the lateral load path and the local response of concrete sleepers and fastening systems at rail seats. On the contrary, the influence of sleeper spacing on the behaviour of railway tracks is only tangible in the distribution of the vertical wheel load. Further, the value of the small gap between the rail and angled guide plate for ‘‘screwed clip systems’’ (or between the insulator and cast-in shoulder for ‘‘driven clip systems’’) has a critical effect on the mechanism of how the lateral load is transferred to the sleeper. That is, as this gap increased the dominant lateral force is imparted to the sleeper in the form of friction force at the concrete-rail pad interface, and the remaining portion of the lateral force is transferred to the angled guide plates (or cast-in shoulders) as a bearing force. The transfer mechanism of lateral load has a large effect on the stress distribution at rail seat and failure modes.
The results of the above-mentioned stage also showed that the loading nature changes at the rail seat area under coinciding vertical and lateral loading compared to the vertical loading case in a form that could have a significant impact on the flexural stress of concrete sleepers, particularly at the midspan section. These findings resulted in the second stage of this study. In this stage, numerical investigations were executed on a concrete sleeper type B70, which meets the requirements of the European standards and Egyptian National Railways (ENR) to evaluate the extent to which lateral loading could affect the structural capacity of the sleeper in the ultimate and normal loading conditions. The numerical findings illustrated that the lateral load significantly reduces the structural capacity of concrete sleepers, particularly at centre sections. from the numerical results, equations were proposed to compute the additional increase in the flexural stress given the lateral load and geometric characteristics of the sleeper. The results also indicated that the interaction of lateral loading with one or more of the following factors could cause the sleeper to reach its ultimate tensile strength and eventually crack: dynamic effects, prestressing loss, and faults at the sleeper-ballast interface.
Finally, based on the two mentioned stages, a methodology was established to consider the effect of lateral load in the design of track components. This methodology aims to improve the design of concrete sleepers and fastening components at curves and mitigate the appearance of various forms of damage. This part included a detailed illustration of specifying the optimal design parameters and safety factors based on lateral loading demand and sleeper characteristics. This methodology, for example, illustrated how to appropriately select the grade of concrete material and the rail pad properties (material type, geometry, etc.). With this methodology, the structural capacity of the concrete sleepers was explored, which are currently used in the Egyptian railways, and the cases of crack occurrence were illustrated. The extent to which this capacity could be influenced by the presence of faults at the sleeper-ballast interface was also investigated. Further, this methodology indicated the significance of including the effect of lateral load in the design to reduce the cracking probability of concrete sleepers during the design life and its effect on the optimal selection of factors used to design concrete sleepers.