A new constraint-based approach for overhaul project scheduling with work space constraints

In overhaul projects, work space constraints limit the simultaneous processing of any pair of jobs requiring the same physical location. Work space constraints can introduce permanent disjunctive constraints that can force stronger limitations than precedence constraints and the critical path calculation can give a false indication of the critical activities and the minimum project duration. Consequently, the use of heuristic scheduling rules based on CPM calculation often causes activities to be scheduled in an improper sequence. This paper introduces a new priority based heuristic procedure where resource allocations are determined at every scheduling decision time point based on the currently active precedence and work space constraints imposed on the schedulable activities. The proposed heuristic rule, called MAXCON, prioritizes the activity which generates the largest lower bound for the remaining project duration at the present scheduling time. Numerical comparison using a set of 300 test problems and a real case shows that the proposed procedure performs better than well reputed heuristic rules. Significance: Work space limitations often affect the conduct of an equipment overhaul project. Several real life overhaul plans turned to be infeasible since resource allocation is often based on precedence constraints only. A modified scheduling heuristic which considers work space constraints is presented in this paper.