Browsing by Author "Kedir, Abdu"

Now showing 1 - 2 of 2
  • No Thumbnail Available
    Item
    Assessment of Degradation and Performance Improvement of Railway Ballast with Geosynthetics - A Case Study of National Railway Network
    (Addis Ababa University, 2015-05) Kedir, Abdu; Henok, Fikre (PhD); Matias, Kabtamu (Mr.)
    The increasing demands of higher axle loads, speeds and usage means understanding the ballast behavior and its interaction with the infrastructure remains a critical element to the design and successful operation of ballasted railway track, Therefore it is important to study the degradation of ballast to increase and predict ballast life on the track, reduce waste track, keep good track quality and minimize the frequency and cost of ballast replacement. The primary objectives of this thesis are to identify the major source of ballast degradation, minimizing the ballast degradation, improve the performance of the ballast as well as the track, to avoid repeated maintenance by minimizing the ballast degradation and finally minimizing ballast degradation of railway line mainly using geosynthetics materials namely Geocells and Geogrids. Literatures have been thoroughly reviewed and the preliminary analysis were performed prior to the Finite Element Method (FEM) analysis with the software ANSYS. The analysis is comprised of typical unreinforced and geocell and geogrid reinforced ballast section of National Railway Network; track settlement, subgrade stress and subgrade stress - strain have been observed. Assessments have been made and promising results are obtained. The result of the finite element analysis (FEA) shows that ballast embankment reinforced with geocell have reduced the track settlement and the subgrade stress beside this the intrusion of geocell in the ballast provides a more linear stress-strain distribution. Ballast embankment reinforced with geogrid was also analyzed; the ballast was reinforced at the ballast-subballast interface and within the ballast. The reinforcement at the ballast-subballast interface have reduced the track settlement and the subgrade stress much better than geogrid reinforcement within the ballast and in both cases a linear stress-strain distribution is obtained. Finally conclusions were made that show geocell and geogrid improved the performance of weak degraded ballast and fresh good quality ballast. Also using reinforced ballast embankment on soft subgrade reduced and distributes stress more evenly as well as reduced the track settlement.
  • No Thumbnail Available
    Item
    Technical Efficiency of Selected Hospitals in Addis Ababa: Data Envelopment Analysis Approach
    (Addis Ababa University, 2006-07) Kedir, Abdu; Demeke, Mulat (PhD)
    The study measured the technical efficiency of seventeen hospitals in Addis Ababa using a five year panel data(2000/01-2004/05) employing both parametric and non-parametric models. We used DEA and DEA-Malmquist models (non-parametric approach) to identify the level of efficiency of hospitals, while determinants of technical efficiency were examined using a censored-Tobit regression model (parametric approach). Results of the CRS DEA model showed that 5(29.4%) hospitals were found technically Efficient, while 12(70.6%) were inefficient. The VRS DEA model indicated 9(52.9%) Hospitals were technically efficient and 8(47.1%) Hosppitals were technically inefficient. Out of the sampled hospitals, 5(29.4%) hospitals were found scale efficient, while12 (70.6%) were scale inefficient. The results of the censored-Tobit model indicated that age, size, teaching status, average bed occupancy rate and number of medical doctors to total staff were found significantly associated with technical efficiency scores.