An applicable method for modifying over-allocated multi-mode resource constraint schedules in the presence of preemptive resources

The issue resource over-allocating is a big concern for project engineers in the process of scheduling project activities. Resources over-allocating are frequently seen after scheduling of a project in practice which causes the schedule to be useless. Modifying an over-allocated schedule is very complicated and needs a lot of efforts and time. In this research a new method is developed for modifying over-allocated schedules in multi-mode resource constrained project scheduling problems with positive cash flows (MRCPSP-PDC). The aim is maximizing net present value of the MRCPSPs (or logically minimizing negative cash flows). The proposed method is designed to consider all types of activity precedence including Finish to Start, Start to Start, Finish to Finish and Start to Finish and also lags between activities. It can also be used alone or as a macro in Microsoft Office Project(Formula presented.) Software to modify resource over-allocated days after scheduling a project. In this research progress payment method and preemptive resources are considered. The proposed approach maximizes NPV by scheduling activities through the resource calendar respecting to the available level of pre-emptive resources and activity numbers. To examine the performance of the proposed method a number of experiments that is derived from the literature are solved. The results are then compared with the state where resource constraints are relaxed and also Simulated Annealing algorithm. The outcomes show that the proposed algorithm can provide modified schedules with no over-allocated days for experiment with 1000 activities and 100 preemptive resources in a few seconds. The method is then applied for scheduling a manufacturing project in practice.