Integer-Programming-Assisted Path-Float-Based Method for Time-Cost Tradeoff Optimization in Project Planning

Abstract

In theory, time-cost tradeoff (TCT) optimization 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 algorithm for TCT optimization that takes advantage of a path-float based scheduling technique and integer programming (IP). The project duration can be shortened in each iteration based on path lengths; 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 by elimination of backward pass and finds optimal or near optimal solutions in terms of lowest project cost or shortest project duration. Since only a part of the network (critical paths) is modelled in IP formulation in each intermediate cycle, the complexity of IP formulation plus the search space is substantially reduced. Case studies are used to verify the proposed method and demonstrate its application. The proposed method can be automated to tackle large project networks commonly encountered in (1) project planning and scheduling and (2) acceleration planning and workface planning in construction management.