Constraint Modeling and Buffer Management With Integrated Production Scheduler

K.H. Chua David1 & Li Jun Shen2

1Assoc. Prof., Dept. of Civ. Engrg., Nat. Univ. of Singapore, 10 Kent Ridge Crescent, Singapore 119260. 65/874-2195, E-mail:
2Research Scholar, Dept. of Civil Engrg., National Univ. of Singapore, 10 Kent Ridge Crescent, Singapore 119260, 65/874-6498, Email:


Constraint modeling is a necessary step in construction planning. The basic CPM approach provides a simple and practical means for resolving time-related precedence constraints between activities. However, most CPM-based tools do not support dealing with the constraints regarding resource and information availabilities at the productionlevel planning phase. When these constraints are concealed in the work plan, it is difficult to assure that they are removed in time so that work takes place as planned. Consequently, the reliability of work plans/assignments will be reduced. This paper presents a scheduling tool called integrated production scheduler (IPS) to handle the nonprecedence constraints in supply chain and information flow. The IPS has three main objectives to be fulfilled. The first is to promote work plan reliability. The second is to increase resource utilization and throughput based on the estimated resource profile. The third is to maintain a stable work flow through reducing uncertainties in the supply chain and information flow. To further facilitate reliable planning, a set of schedule buffers are established to help manage the constraints. Specifically, the working buffer and the shielding buffer ensure quality assignments by removing resource conflicts and supply chain uncertainties. The pulling buffer and the screening buffer increase resource and information availabilities by managing the delivery issues in advance. With the proposed schedule buffer management, it is feasible to enhance the reliability of look-ahead plans and consequently achieve lean process management.


Constraint, buffer management, lean construction, look-ahead planning, Integrated Production Scheduler.



David, K.C. & Shen, L.J. 2001, 'Constraint Modeling and Buffer Management With Integrated Production Scheduler' In:, Ballard, G. & Chua, D., 9th Annual Conference of the International Group for Lean Construction. Singapore, Singapore, 6-8 Aug 2001.

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