Abstract: The reliability of a project completion time projection (PCT) is of significant concern to project managers, because it profoundly affects how a project is executed. Traditionally, such reliability has been treated as a time-independent variable, although the reliability of the PCT varies throughout the construction period. Little research has looked at the effect of time on the reliability of PCTs. This paper takes a new look at the probabilistic project scheduling problem by proposing a time-dependent reliability model for assessing the reliability of PCTs throughout construction. Ideas from time-dependent reliability theory and series system modeling are applied. A construction project is analyzed to illustrate the performance of the proposed method. It is found that that time-dependent reliability analysis is more appropriate for probabilistic project scheduling, and ignoring the time effect may lead to unrealistic estimates for probabilistic planning. It is also found that the proposed model is fast and accurate, compared to Monte Carlo analysis. The main contribution of this paper lies in incorporating the time-dependent variable in the project network scheduling problem.
