A multi-objective constraint programming–satisfiability model for non-unit repetitive construction scheduling

Abstract

Non-unit repetitive construction projects, in which activity groups are repeatedly executed over work-group-specific units rather than over a common set of identical production units, are difficult to schedule because activity sequences, crew movements, and execution logic vary across crew options. This study develops a multi-objective Constraint Programming–Satisfiability (CP-SAT) model for non-unit repetitive construction scheduling. The model integrates crew–option selection, interval-based scheduling, route-based crew logic, transfer-dependent travel times, optional interruption, and sequence control within a unified framework. Both soft and hard sequencing requirements are represented: soft sequences emerge from optimized crew routes, while hard sequences can enforce prescribed order, same-crew execution, and immediate-successor relationships when required. An exact ε-constraint procedure is used for the bi-objective time-cost case, while sampled frontier generation supports higher-dimensional trade-off analysis. From a practical perspective, the framework helps project managers compare feasible scheduling alternatives and balance competing priorities related to project deadlines, budget, construction quality, and crew continuity. The proposed model therefore provides a rigorous and practical decision-support framework for complex non-unit repetitive construction projects.