Efficient modeling of time-cost trade-off problem by eliminating redundant paths

Time-cost trade-off (TCTO) is a traditional decision-making problem in construction management. Numerous optimization techniques have been developed to solve such problem; however, they are not applicable to large-sized projects. Although heuristic methods can handle large-sized problems, they do not guarantee optimum solution. In a project network, the proper sequence of activities can be maintained by allowing a precedence constraint for each path. In practice, only small number of paths are dominant while others are redundant. In this paper, an efficient optimization model is developed to minimize project direct cost where redundant paths are eliminated, precise activity discrete time-cost relationship is used and overlap between activities is permitted. The optimization model is formulated in the standard form of zero-one programming. The model requires as inputs: discrete utility data of activities, precedence relationships and overlap between consecutive activities. Details of model formulation is illustrated by an example project and then is validated by a real-life project. Based on the obtained results, the developed model is compared with traditional optimization models. The developed model guarantees optimal solution and can be applied efficiently to large-sized projects. The proposed approach provides both academicians and practitioners with an efficient technique that produces optimal solution based on realistic assumptions.