A priority-rule method for project scheduling with work-content constraints

The activities of a project are in general characterized by a work content in terms of resource-time units, e.g. person-days. Even though most project scheduling models assume a time-invariant resource usage, normally it is possible to vary the resource usage during the execution of an activity. Typically, a lower and an upper bound on this resource usage and a minimum time lag between consecutive changes of this resource usage are prescribed. The project scheduling problem studied in this paper consists in determining a feasible resource-usage profile for each activity such that the project duration is minimized subject to precedence and resource-capacity constraints. While the known solution methods interpret the prescribed work content as a lower bound, we assume that each activity's work content must be processed exactly. We propose a priority-rule scheduling method that iteratively determines a feasible resource-usage profile for each activity. We present a consistency test for constructing such profiles more efficiently. Our computational results demonstrate that the new method solves more instances to feasibility than two benchmark procedures, and is suited for project instances with up to 200 activities.