Scheduling overtime in construction using time-cost trade-off

Schedule overrun is a major problem in construction industry impacting all parties involved. It may cause cost overrun or litigation between the parties. Several techniques may be used to crash activity duration in order to compress project duration. However, in practice, it is still complicated to identify which activities in a project will be crashed and for what amount of activity duration in order to achieve the project duration required at the minimum additional cost. This study selects overtime as a crashing technique and Time-Cost Trade-Off (TCTO) as an analyzing technique. The overtime is integrated into TCTO model. The model includes two overtime schemes: 5–10's and 6–10's with and without productivity loss. The overtime scheme that incorporates productivity loss into time-cost function uses productivity efficiency factors from BRT (1980). An algorithm for derivation of time-cost functions from overtime is developed. PDM network is used to develop the model, after which the model is solved by Excel Add-In solver. The model can be used to find project duration boundary, project time constraint solution, the most economic solution, and project cost curve. A computer program is presented and tested by comparing the solutions from the program with those manually solved. The result shows that the computer program is successfully developed. Each solution from 5–10 and 6–10 overtime schemes with and without productivity loss are compared. The outcome shows that the 6–10 overtime scheme surpasses the 5–10 overtime scheme by giving lower overtime cost and achieving lower minimum project duration.