Key Constraint Analysis: Achieve Lean Processes with the Application of TOC

Constraint modeling provides an unambiguous means to identify the causes of uncertainties in the construction workflow and consequently it is possible to improve plan reliability and project performance by tackling these constraints in time following certain methodologies and strategies. Besides precedence and resource allocation constraints, another type of constraints regarding the availabilities of resources and information (RI) prerequisites should be explicitly handled in the work plan. Resolving RI availability constraints is a necessary step in low-level project planning to reduce uncertainties in the supply chain and information flow, enhance plan reliability, and achieve lean process in terms of fewer delays and less schedule disturbance. Among various RI constraints, some result in more adverse impact to project completion than those of others. According to the theory of constraints (TOC), the overall system performance of a production process may be confined by a few critical constraints which should be eliminated with higher priority. Such constraints are collectively called key constraints, the removal of which would directly improve project performance. This paper provides a methodology to prioritize the RI constraints and identify the key constraints for effectively reducing project delays with minimum impact on schedule changes. The application of key constraint analysis has been implemented with the Integrated Production Scheduler (IPS), a constraint-based planning and scheduling tool which fulfills the principles of lean project management. An illustrative example is provided to demonstrate the application of key constraint determination and resolution to eliminate project delay through resolving the key constraints step by step.