Year

1997

Degree Name

Doctor of Philosophy

Department

Department of Civil and Mining Engineering

Abstract

There is a need to improve the current understanding of the behaviour of the track system and its components and to develop an analytical model of the track system with its complete solution procedure. Towards this aim, a theoretical and experimental study is made on the track system in this research work.

A new theoretical model for the track system is developed. This model consists of the track elements and considers important factors omitted in previous models. The methodology, derivation of the equations, and the solution procedure of the model are presented. Several numerical examples are solved using this model, and the importance of the new factors considered in the model is discussed. Track modelling is improved by the consideration of important parameters in this model. These parameters include: (1) properties of the sub-structure of the track, (2) boundary dampers at the subgrade boundaries, and (3) time dependent characteristics of the load.

A three dimensional model of track is developed using a finite element computer package. Several computer models are developed from this model for different properties and conditions of the track system. Using these models, optimisation of track models is investigated and minimum geometrical requirements in track models are found. A sensitivity analysis is conducted on the computer models, to provide guides for the optimisation of the track system.

The utilisation of two methods of in-situ tests on track ground base materials is investigated using experimental results. The properties of the ballast and subgrade materials are studied, using a wide range of results obtained from laboratory tests. This leads to the development of three models for the stress-strain relationship, permanent strain, and failure criteria of these materials. A methodology is developed to utilise these models when modelling the track system.

Several experimental works are conducted on the track system and its components. Rail deflections are calculated from the time-displacement obtained from the rail. Modal analysis tests are conducted on the track system and sleepers. Three methods of tests on sleepers are utilised to determine damping properties of sleepers. The results of tests on isolated sleepers, a track test bed, and a track field are presented and discussed. The characteristics of the track components are discussed using the results obtained from the experiments.

The efficiency of the new models and the importance of the new developments made in this research are discussed. Theoretical and experimental results are compared. Conclusions and guides are provided for the improvement of track models and optimisation of the track system. Recommendations and suggestions are made for further research in this area.

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