Time – Cost Relationships for Public Road Construction Projects in Ethiopia
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Date
2008-05
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Addis Ababa University
Abstract
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.
Description
Keywords
Construction Management; Time - Cost Relationship; Bromilow’s Principle; Scurve; Earned Value Management.