Critical Path Method in Construction Industry

Critical Path Method (CPM) is a project management method created in 1958 in American company DuPont to improve internal production processes. Since then the method is widely used in industries such as construction, aerospace, defense, engineering, research and many more. However, this article focuses on its use in civil engineering industry and construction. The method is suitable for all kind of construction projects that require many independent activities to be completed.

Critical path is a sequence of activities that lead to the shortest possible completion of the project. These activities are called critical activities and every delay in each of these activities will result in delay of the whole project. This article depicts ways of using the method to analyze projects as a several groups of activities to reduce the bottleneck points and finish the project on time and within the budget. Methodology of creation of the basic CPM direct acyclic graph (DAG) is presented in a way of short step-by-step tutorial.

Construction projects, although very complicated are similar or even identical in a way of having similar unit activities and resources. Scheduling in linear construction projects require use of aforementioned resources from one activity to another in such a way, that continuity and logic between network activities is sustained. In the article the procedure for CPM-based scheduling in linear construction projects is described and explained. Moreover, Resource Activity Critical Path Method (RACPM) is presented based on Hong Kong Polytechnic University practical method based on the additional dimension of time added to the dimension of time. As a summary, advantages and disadvantages of the method are described as well as limitations to the use of CP-method. At the end of the article annotated bibliography with reference links is provided.

Big idea

Short history

While the method itself has been created in 1958 its induction to construction industry happened awhile later. There are always two stages recognized while implementing the method: first stage, when there has been an initial interest aroused in the industry and second, while the overall effects on the industry are known. It took as long as in 1968 when the method was known well enough to consider it to be in its second stage – mainly due to time-consuming characteristic of construction projects. Nevertheless, the method was adapted to specifics of civil and construction projects’ characteristic and was successfully used in the industry ever since.

Evolution

What helped CPM to be more and more popular was that it was of great utility while managing bigger projects – the method was immediately implemented to projects of value higher than £100’000 (value from 1968, approx. £2’000’000 nowadays). The method itself has not changed much in terms of its methodology. Algorithms of calculation of critical path remain the same. What changed significantly is the use of the computers in its implementation to the projects. Back when the method was created hand calculations were common almost for all of the projects, at least for tender stages. Project managers mentioned from 50 up to 600 activities as a range for hand calculations using CPM. Nowadays various types of software is used i.a. Primavera, MS Project or various spreadsheets.

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