Browsing by Author "Shimelis, Assefa"

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    Modeling and Analyzing the Deformation of Ballast Structure Due to Repetition of Loads
    (Addis Ababa University, 2015-12) Shimelis, Assefa; Abdulsetar, Siraj (Mr.)
    The issue of permanent deformation of ballast structure due to repetition of loads is the most important element in railway maintenance planning and policy making. It affects the general operation and management of railway transportation plus the overall costs of track structure and its life spans. To allow a safe, reliable and efficient rail network and to provide a good ride quality, the vertical profile of a railway track has to be maintained at a satisfactory level. And timely maintenance of ballast structure is essential to provide continuous service at reasonable costs since the track permanent deformation is a function of traffic load, environmental condition and track structure response behavior to the applied loads at different times of service life. Although most of the time deterioration process is very slow, but it might lead to massive failures with an enormous financial lose. This research determines the permanent deformation of railway ballast, particularly the vertical settlement under repeated traffic loading. Experimental data reviewed in the literature were assumed to represent the ballast materials used in LRT projects. After initial elastic modeling, the extended Drucker-Prager model with hardening, which simulates the initial plastic deformation of granular materials under cyclic loads, were used in the FEM analysis in order to account for the inelastic behavior of railway ballast. Besides, FEM analysis provides the information to predict railway ballast deformation in terms of number of loading under wheel loading. And it can be observed that the vertical stresses were concentrated underneath the sleeper and ballast permanent deformation is increasing exponentially with increasing number of loading cycles and deform non- linearly with increasing depths of ballast.