Formalizing construction sequence constraints for the rapid generation of scheduling alternatives

Construction planners today use CPM-based schedules to describe the sequence of work for a project. A CPM schedule describes the logic for activity sequences using precedence relationships that represent the temporal aspects of constraints. However, precedence relationships do not represent the rationale behind activity sequences, which make it difficult for planners to interpret the logic behind constraints, and whether constraints may or may not be relaxed. The absence of sequencing rationale make it particularly difficult for planners to re-sequence activities to meet changing project demands. Planners re-sequence activities by determining the “role” and “status” of activities (i.e. , whether activities may or may not be delayed) based on the rationale behind constraints. Currently, inferring the role and status of activities using CPM-based schedules can only be performed in the planners' minds. Hence, planners need a way to represent the rationale for constraints in CPM schedules and mechanisms that support planners in developing sequencing alternatives correctly and rapidly. This research addressed these requirements by formalizing (1) an ontology that enables planners to describe their rationale for constraints explicitly, (2) a “classification” mechanism that automatically infers the role and status of activities given a “constraint-loaded” schedule, and (3) a process that generically models how planners use the classified activities to identify activities to delay and prioritize activities when developing sequencing alternatives. The formalizations were validated by performing three retrospective test cases and one charrette test using prototype software, CLCPM. The tests demonstrated that the formalizations support planners in describing different types of construction sequencing rationale correctly and consistently, and also in developing sequencing alternatives rapidly for construction schedules representing different types of construction work. Practically, the formalizations provide an environment that enables multiple project members to better communicate the logic of activity sequences, better understand the individual role and impact of activity sequences between project members, and evaluate sequencing scenarios more quickly and consistently within group settings.