Graphical Evaluation and Review Technique (GERT): The Panorama in the Computation and Visualization of Network-Based Project Management

Graphical Evaluation and Review Technique (GERT): The Panorama in the Computation and Visualization of Network-Based Project Management

Ramesh Kannan (VIT Chennai, India)
Copyright: © 2014 |Pages: 15
DOI: 10.4018/978-1-4666-4940-8.ch009
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This chapter focuses primarily on Graphical Evaluation and Review Technique (GERT), one of the intriguing techniques used for network-based management. It is a stochastic network technique and has many advantages over the conventional Critical Path Method (CPM) and Programme Evaluation and Review Techniques used for project management. The formulation of the GERT network for linear situation can be development by analytical techniques (such as signal flow graph theory); thus for a non-linear and other complex conditions, the Q-GERT (included Queueing Concepts) is used. To reinforce the importance of GERT and Q-GERT, a firm study is carried out on the limitations of the CPM and PERT. Thus, a solid comparison of GERT network with the CPM and PERT network is done not only to emphasize the applicability of the network but also to validate of the network. The scheduling of concrete formwork systems are considered for the comparison.
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The representation of activities in a project in the form of network is one of the most important and simplest techniques adapted in the project management. The reasons for the adaptation of network-based project management are

  • it can be used to model complex project by fragmenting into simpler network of interrelated activities of the entire systems,

  • the computation of the project attributes requires minimum time and are highly reliable,

  • it serves as a better communication aid among different project associates involved in the project,

  • above all it is the best method of data visualisation and specifying data requirement for the modelling, analysis and design of multifarious projects.

The network-based project management has wide range of applications includes Industrial Engineering, production and manufacturing, contract management, construction project management, operation research, software project management and so on (Pristker, 1977). The most popular and commonly used techniques in the network-based project management are Critical Path Method (CPM) and Programme Evaluation and Review Technique (PERT). However these techniques have inherent drawbacks that the results obtained are not highly reliable and thus an intriguing technique which incorporates the human-factor (Pristker, 1977) into consideration is needed. One such network technique is the Graphical Evaluation and Review Technique (GERT). This chapter illustrates the advantages of GERT over CPM and PERT. The GERT technique is applied to the scheduling of concrete formwork systems to reinforce the importance of GERT over other project network techniques.


Project Network Techniques

Critical Path Method (CPM)

The Critical Path Method (CPM) was first developed by Morgan R. Walker of the Engineering Services Division of DuPont and James E. Kelly Jr. of Remington Rand in 1957 (Baboulene, 1970). Later was developed considering not only the logical dependencies between the activities but also the inclusion of resource related to each activity. CPM is generally regarded as the activity oriented networks.

The CPM includes categorization of all activities in the project known as work breakdown structure by a technique called arrow diagramming (Martino, 1970), determination of duration of the activities, determination of critical activities (activities having maximum duration) and the formulation of Critical Path (path associated with the critical activities) in otherwords the path associated with the longer duration as shown in Figure 1. Ultimately the network is modeled as a linear relationship between cost and time.

Figure 1.

Typical CPM network diagram (Single-time estimate)


The most important thing to be considered in the CPM is that it is can be applied only to the activities associated with the deterministic durations (Baboulene, 1970). The CPM can be used to obtain feasible solution for the Least-cost scheduling. However, CPM accounts only for the determination of the earliest completion time but not probable completion time of the project.

Activity-on-arrow technique used to compute CPM was still in use however the Activity-on-node is mostly preferred as shown in Figure 2.

Figure 2.

Graphical representation of the (a) Activity-on-arrow diagram, (b) Activity-on-node diagram


The CPM is very effective but suffers seriously on the fact that it requires deterministic time, however the project durations cannot be altered or incase of any delay in the project, it is highly difficult to resolve or retrieve the activities and sometimes it would even lead to the collapse of entire network.

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