Time-Cost Trade-Off in Repetitive Projects with Soft Logic

Several mathematical models have been developed for cost optimization in repetitive projects. These models aim at defining the optimum output rate for each repetitive activity that yields the minimum overall cost of the project. However, all these models assume that there is only one logical sequence of the activities in a project while in the real-world projects, the logic between activities can be divided into fixed logic and soft logic. The fixed logic provides only a logic sequence of the construction activities. On the other hand, soft logic provides other possibilities of analyzing the activities. When faced with a project involving many repetitive activities with soft logics, the more NAOT (Number of working units which a repetitive Activity can precede at One Time) provided for each repetitive activities, the less project duration may be but the more project cost is required. Similar to traditional time-cost trade-off problems, the challenging question confronting the planner will be more than the optimum output rate for each repetitive activity that yields the minimum overall cost, but also which is the optimum NAOT for each repetitive activity that yields the minimum overall cost. This paper applies dynamic programming and presents a new formulation with consideration of soft logics defining the optimum output rate as well as NAOT for each repetitive activity that yields the minimum overall cost.