GANTT

Revision as of 11:59, 18 February 2021

Written by Søren Emil Kjær

Abstract

The Gantt chart as a tool is one of the keystones within the project schedule management discipline. (1). Invented by Henry Laurence Gantt in the second decade of the 20th century the tool was initially used as a visual representation of the time schedule and progress of a given project. (3). This is very much linked up with the definition of the word project, which is defined as a set of activities which has a definite beginning and a definite end. (3) Gantt charts used to be a laborious process, since it was only possible to create them manually by hand. That has since changed and at the time of writing the Gantt chart has undergone a major development since its first introduction. The purpose of this article is to create an understanding of how to use Gantt charts in the 21st century and provide guidance on how to use them specially for project managers. What fundamental insight to obtain before implementing a Gantt chart and how to work with your Gantt chart once it is implemented. Furthermore, how to use Gantt charts together with other project schedule management tools and how that collaboration can create value for the project. The article will also present different types of software to use when working with Gantt charts and how that software has evolved the Gantt chart. Conclusively the article will present the limitations of Gantt charts as a tool by defining when, where and by whom the tool is not applicable.

Big Idea

A Gantt chart consists of bars displayed against time. Each bar represents an activity, and the length of a bar indicates the time consumption of the given activity. The left-hand side of a bar represents the beginning of an activity and the right-hand side of a bar marks the completion of an activity. The time axis is dependent on the detail level of the chart and can therefore represent units such as years, months, days and so forth. This can be derived from figure 1, which displays the simple algorithm of the Gantt chart. The progress during the project can be linked to the Gantt chart and be tracked with a vertical line that represents the current date. Furthermore, so-called milestones can be implemented in the chart. Milestones represent key project deliverables such as the first test flight of a new airplane. This allows the project manager to obtain a better overview of the project and its time schedule and therefore enables a greater probability of the project becoming a success with regards to the project schedule management. To create a Gantt chart with sufficient and robust information it is necessary to implement the Work Breakdown Structure (WBS) method. The purpose of the WBS is to identify and segment all the different activities that defines the entire project. (2). By doing so the Gantt chart becomes highly detailed and creates a manageable chart of the entire project where constraints such as overlapping activities and dependencies can be outlined. The purpose of a Gantt chart is to outline and monitor the time schedule of a project. This is enabled by making it a very graphical and intuitive tool to use, hence why it is so widely used in the discipline of project schedule management around the world. The technological advances in our modern-day society have made the use of Gantt charts a lot easier and with basic knowledge and skills it is possible to create Gantt charts using simple computer software such as Microsoft Projects. (kilde). This will be further elaborated on in the latter part of the article.

Application

The Gantt chart is applicable in the majority of projects, but there are some key steps that has to be performed in order for the chart to become useful for the project manager. It is important to note that a Gantt chart is a dynamic tool which has to be managed along the project.

The first step is to define the activities that makes up the project. In this step it is advantageous to implement the Work Breakdown Structure (WBS) in order to break down the project into manageable activities. If done correctly this should allow the project manager to get a complete overview of the entire project and its activities. The detail level of this WBS is equal to the complexity of the Gantt chart.

The second step is to sequence the activities. To create a feasible schedule using a Gantt chart it is important to know in what order the different activities must be performed. Therefore, the dependencies of the activities must be clarified. There are 4 major dependencies regarding the Gantt chart:

Finish-to-start (FS): Activity a must finish before activity b can begin. Example, the foundation of a building must be finished before the walls can be built.

Start-to-finish (SF): Activity a must start before activity b can finish. Example, the electrician, representing activity a, pulled all the wiring in the wall framing. He only needs to put up the electrical outlet plugs to finish. Before that is possible, the carpenter, representing activity b, must put up the remaining part of the wall.

Finish-to-finish (FF): Activity a must finish before activity b can finish. Example, the carpenter from before, now representing activity a, is done with the all the walls. The painter, representing activity b, has been painting the walls as the carpenter finished them. Now that the carpenter is entirely done, the painter is able to finish his activity.

Start-to-start (SS): Activity a must start, before activity b can start. Example, the carpenter from before, representing activity a must begin putting up the walls, before the painter, representing task b, can begin painting them.

In coherence with the above-mentioned dependencies there are other important factors to take into consideration. The lead and lag times are crucial to the overall project schedule management.

Lead time: This is an optimization tool that can be used to compress the overall time consumption of the activities in the project. This is done by recognizing which activities can be performed in parallel or in partial parallel. Lead time is refereeing to the overlap in activities. As shown in figure x, this means that the activities are being performed simultaneously and therefore saving time. Lead time can only be implemented on activities which are defined as being of the type Finish-to-start. An example of the implementation of lead time is our previous example of the painter and carpenter. As soon as the carpenter has finished a certain amount of walls the painter was able to begin his activity. Presuming that the painter will not paint faster than the carpenter can build the walls. They would be able to finish their activities in sequence.

Lag time: This works like a constraint. Lag time describes the time in between activities. For the lag time to occur there has to be a dependency between the activities. So that activity b cannot begin before activity a is finished. Lag time can develop in all 4 major dependencies described earlier in this article. It is inevitable to get through a project without lag time. Figure x aims to show the visual representation of lag time. An example of lag time is the concrete foundation of a building. Once the concrete is poured there will be a timeframe where the project has to wait on the concrete to dry and develop sufficient strength so that work can continue. This is the essence of lag time. By taking lag time into consideration when creating a Gantt chart the project manager is able to pinpoint the obstacles in the project and plan for them. This hinders the possibilities of delays.

The third step is to estimate activity durations. In this step the time consumption of each activity is allocated. These time approximations are to be based upon the individual dependencies of the activities. It is in this step that the project manager can begin to use all the information presented in this article. By setting up the Gantt chart with all the activities and their dependencies and individual lead and lag times – a complete overview of the project is created. This enables the project manager to define the key milestones. From this information the project manager is able to derive the Critical Path Method (CPM). This method outlines the critical activities of a project. The activities on the CP will delay the entire project if the time consumption of these are violated. An activity on the CP cannot begin before it’s foregoing activity is finished. The knowledge of the CP allows the project manager to navigate in the project and ensure that the critical activities are managed.

By completing these steps, the Gantt chart is now complete, and the project is visualized. The next step is to allocate recourses to each individual activity. The amount of recourses are linked with the time consumption of each activity. By doing so you enable the possibility of reworking you chart during the course of the project. This leads to the option of managing the Gantt chart with schedule compression techniques. There are 2 major techniques:

Crashing: Relates to the technique were adding recourses to a specific activity will decrease the time consumption. This could be in the form of working overtime, assigning more workers et cetera. This technique can only be implemented on activities that are located on the critical path. When applying crashing the project manager increases the risk of the project due to the addition of cost.

Fast Tracking: The purpose of this technique is to implement as much lead time as possible. This is done by overlapping activities as much as possible. This is of course only possible in some cases. It would be catastrophically to overlap certain activities. Fast tracking increases the risk of the project since activities are compressed and there is less room for error in the individual activities. The cost will also increase since the amount of work is increased.

Figure x presents the visual representation of the schedule compression techniques.

Limitations

Annotated bibliography

References

(1)Project Management Institute, Inc. (PMI) (2017), Guide to the Project Management Body of Knowledge (PMBOK® Guide) (6th Edition).

(2)National Aeronautics and Space Administration (2010), NASA Work Breakdown Structure (WBS) Handbook.

(3)Pankaja Pradeep Kumar, CCE, (2005), Effective Use of Gantt Chart for Managing Large Scale Projects, AACE International, Cost Engineering Vol. 47/No. 7.