Failure of CPM and PERT

Construction Scheduling

Friday, January 20, 2017

Failure of CPM and PERT in Construction

There have been various presentations of networks for various uses, and the construction industry has tried out the CPM and PERT variations with unsatisfactory results mainly due to their incompatibility to the essence of the construction scheduling process.

Failure of the majority of construction contractors to fully use CPM or PERT or both, and adopt it as a basic construction management technique, exposes that there is some fundamental failure in the CPM / PERT network technique. This unwillingness flies in the face of a great deal of publicity promoting the use of CPM/PERT approach to construction scheduling. If some contractors have to provide a CPM/PERT network in the bid at the request of the client, they usually employ an outside consultant to do it, pass his fee on to the client as part of the bid, and continue to manage their project with more appropriate manner.

Only a few people have considered whether or not the CPM / PERT model is of good fit to the construction process and of sufficient fit to be used to increase the efficiency of the people working in the construction processes. 

It is suggested that the basic critical path network technique is neither a true model nor the best approximate model of the construction process.

The concept of CPM and PERT was created in the military/industrial environment where United States National Security put a low weighing on cost control and efficient use of resources. The specific project being planned and controlled was of greater importance than efficient use of individual resources. In Construction, the normal project is not of national importance, and each subcontractor is very interested in the efficient use of his resources on all projects he is working on. This creates a different situation and environment from that of the origins of CPM and PERT. Put simply, for those who control the construction resources, minimum consumption of resources on a normal construction project is more desirable than minimum calendar duration for the whole project. At the very least, minimizing cost is to be considered as much an objective as minimizing overall durations.

Just as human bodies usually reject medically transplanted organ from other non-related humans, there should be little wonder that the construction industry has, to a large extent, rejected the transplant of CPM and PERT into its body.

The CPM / PERT concepts, while useful in other industries, are comparatively foreign to the construction scheduling process which has heuristically evolved over centuries to satisfy the needs of the situation of construction. It follows that a scheduling concept for construction drawn from that heuristic analysis to the processes of construction can be more realistic and thus more useful concept of scheduling for the construction industry.

The above is quoted from a published paper by S. Birrell

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