Browsing by Author "Assefa, Abraham"

Now showing 1 - 2 of 2
  • No Thumbnail Available
    Item
    Study on Quality of Site Concrete Production and its Management Practice in Addis Ababa Housing Projects (Case study on Koye Feche housing Projects)
    (Addis Ababa University, 2017-03) Assefa, Abraham; Sisay, Habtamu(PhD)
    Concrete, because of its versatility in use, is a major component of most of our infrastructural facilities today. The quality of concrete is affected by its constituent materials, the equipment used and the workmanship in concrete production process. A better or poor concrete may be made of exactly the same ingredients based on the quality control practice of the production process. The city administration of Addis Ababa is building and administering condominium buildings around the city for more than one million house seekers around different project location of Addis Ababa. Most parts of these projects are reinforced concrete structure in which concrete takes the major proportion among the consumed construction materials. This research is carried out on the quality of concrete produced and the quality management practice to enhance concrete quality under projects administered by Addis Ababa housing project office, by taking the Koye Feche site as a case study. The research used literature review, desk study, interview with experts and analysis of compressive strength test results on samples collected from ongoing concrete production sites. Statistical quality control based on compressive strength tests conducted on selected projects reveals that, 40.4% of the test results were found to be defective based on EBCS-2:1995 compliance criteria’s. According to ACI-214 classification, 35.4% of test result based on standard deviation indicates poor quality control whereas 71.25% of the test results show poor quality control practice based on their coefficient of variations. The investigation shows that, the use of poor gradation aggregate and high silt, clay, and dust content of sand, water with impurities, problems with batching which usually called under batching and over batching are major causes of quality problems. Furthermore, lack of attentive control on each production process, lack of management commitment and poor workmanship in quality concrete production is also the most frequent problems identified by respondents. Key Words: AAHDPO, Coefficient of Variation, CQMP, Management Commitment, Quality Control, Standard Deviation, Statistical Quality Control, TQM and Workmanship.
  • No Thumbnail Available
    Item
    Time – Cost Relationships for Public Road Construction Projects in Ethiopia
    (Addis Ababa University, 2008-05) Assefa, Abraham; Jekale, Wubishet(phD)
    This research work has tried to test the time – cost relationship of road projects by using the hypothesized empirical and graphical models developed for the concept. Based on the Empirical Bromilow’s Model, the duration of Ethiopian Federal Road Construction Projects has been modeled by a time - cost formula expressed in the form of T = KCB, where T is the actual construction time in calendar days, C is the final cost of contract in Ethiopia Birr, K is a constant characteristic of time performance, and B is a constant indicative of the sensitivity of time performance to cost level. This thesis applied the relationship to 33 projects based on the two categories International Contractor (IC) and Domestic Contractor (DC) Projects and on the adjusted and unadjusted cost basis. Analysis using both linear and multiple regression technique was performed between project duration (i.e., time), project cost, project length and type of construction (asphalt concrete, double surface treatment, and gravel surface). The analysis results indicated that the above principle is valid to IC projects and is invalid to DC projects based on T – test. Though the Bromilow’s principle has been found to invalid for DC projects, the relationship between contract Time and length has been developed. In addition the research has developed a cost prediction model for IC projects. Based on the Graphical Model, the time – cost relationship has been reviewed by using the cumulative time – cost curve(S – curve) concept and the earned value management techniques (EVM). The applicability of this curve was tested by using two case study projects. The test for smoothness of the curve was carried out by testing the reliability index using Weibull probability functions. In addition to that EVM techniques like Schedule Variance, Schedule Performance Index and Estimate to Completion were used to view their applicability. The analysis results clearly indicated that the S- curve concept is not applicable to the case study projects and the tools of EVM technique are better indicators of the performance than the S – curve. Key Words: Construction Management; Time - Cost relationship; Bromilow’s Principle; SCurve; Earned Value Management.