Path-Float Based Approach to Optimizing Time-Cost Tradeoff in Project Planning and Scheduling

In theory, time-cost tradeoff (TCT) analysis is a classic planning problem appealing to construction management; yet, existing analytical methods are found inadequate to make a significant impact in practice. Heuristic methods lack a theoretical basis to ensure arriving at optimum solutions in solving specific problems; on the other hand, mathematical programming requires cumbersome, complicated formulation. This study proposes a new computing framework for TCT optimization that takes advantage of a path-float based technique and integer programming (IP). The project duration can be shortened in each crashing cycle based on path-float analysis; while IP is nested to inform on which activities on the critical path(s) to shorten by how long duration. The new TCT optimization approach streamlines critical path analysis in each cycle and finds global optimums in terms of lowest project cost or shortest project duration. Because only part of the network (critical path) is considered in IP formulation in each intermediate cycle, the complexity of IP formulation plus the search space is substantially reduced. A case study is used to verify the proposed method and demonstrate its application. The proposed method can be automated to tackle large project networks commonly encountered in workface planning.