The Mechanism of Design Activity Overlapping in Construction Projects and the Time-Cost Tradeoff Function

Abstract

An effective and well known technique for earlier completion of construction projects is to overlap the project activities or phases that normally would be performed in sequence. Overlapping, also called fast-tracking, is inherently risky because it increases uncertainties and can result in more changes and rework. In order to gain maximum advantages from early project completion, a tradeoff between benefits and losses of activity overlapping is required. Such a tradeoff is a type of time-cost tradeoff. Various time-cost tradeoffs have been extensively studied in the project management and construction management literature; however, limited research exists to address the activity overlapping time-cost tradeoff. In this research, the theoretical mechanism of overlapping has been identified through a literature review and interviews with planning and scheduling experts. Then, an objective function that reflects the overlapping time-cost tradeoff is developed. The paper explains the overlapping mechanism in detail, and introduces the suggested objective function. It also shows that the most important negative impact of overlapping design activities is the rework occurring due to incomplete information exchange between activities; such rework has both time and cost impacts on overlapping and should be considered a key parameter in the time-cost tradeoff. The results of this research can generate insights for further research to solve the overlapping time-cost tradeoff and determine the optimum overlapping degree between activities in construction projects.