Scheduling projects with repeating activities

Construction contractors are often faced with projects containing multiple units wherein activities repeat from unit to unit. These projects require schedules that ensure the uninterrupted usage of resources from an activity in one unit to a similar activity in the next unit. The critical path method (CPM) cannot assure this requirement because only technical precedence and resource availability constraints are explicitly shown in CPM networks. The repetitive scheduling method (RSM) described in this paper recognizes the technical constraints of CPM and also includes an additional resource continuity constraint to ensure continuous resource usage. RSM is a scheduling methodology that simplifies and generalizes various multiunit scheduling procedures previously proposed by several authors and it is known by a number of different names. It applies to both vertical and horizontal projects containing either discrete or continuous activities. An RSM schedule is presented graphically as an X-Y plot of a series of production lines, each of which represent a repetitive activity. RSM introduces the control point as a new concept for positioning successive production lines that may either diverge or converge, depending upon their relative slopes. The control point between two successive production lines is located toward the first unit in the sequence of units if the lines diverge, and toward the last unit in the sequence if the lines converge. RSM also introduces the controlling sequence of activities as a new concept for the determination of the project duration. This sequence includes activities between control points on successive unit production lines and extends from project start to project finish. The controlling sequence may include both critical and noncritical activities.