Flexible Scheduling for Construction Projects
Saleh, Mohammad Fahmi Saleh
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A successful project schedule is one of the prime keys to project success. The Critical Path Method (CPM) determines a rigid timeline of activities' execution ignoring resource related issues. Many techniques were developed to enhance CPM performance by taking advantage of the limited allowable flexibility that CPM provides. Resource allocation techniques assume limited resource availability and adjust the CPM schedule accordingly. Such practices will likely result in extended project duration which might not be so convenient to stakeholders. Where time is set as the sole constraint of a project, resource leveling techniques were developed to enhance the shape of the resource histogram by reducing its variations. Current resource leveling techniques took advantage of the only allowable flexibility provided by CPM - moving non-critical activities within available float. Researchers explored more options to further enhance resource leveling by taking into account activity splitting and using different computational approaches to enhance the computing time. This research proposes new enhancements to CPM in order to explore more options in construction scheduling. The proposed approach introduces variability in the CPM schedule by allowing each activity to experience different scenarios of resource loading and working hours. Besides, the consequential changes in durations, productivity-related lags, and productivity losses are taken into consideration, In addition, movements within available lags are included in the model as well. As each activity duration and resources are allowed to vary based on available scenarios, associated productivity losses are calculated to assure effectiveness of the solution. The model tries all the possible combinations of scenarios and finds the best fit for different objectives. III each objective targeted, many cost aspects of the projects are taken into consideration such as hiring/firing, liquidated damages, incentives, overhead and labor cost. This approach is modeled in Excel and solved using an add-in that solves non-linear integer problems called "What'sBest". The results of this approach reflected new trade-offs in construction scheduling for different objectives. With resource leveling, the approach could achieve histograms with fewer variations, if not perfectly leveled, in exchange of marginal additional cost and less efficiency of workers. For resource allocation, the model outperforms the classical techniques resource allocation by attaining shorter schedules, smoother histograms, and lower overall project cost. The model also reflected better results in cost optimization and cost optimization with resource constraints. In other words, a new hi-polar trade-off is introduced among time, cost, and efficiency. This approach is referred to as "Flexible Scheduling".