GANTT

Written by Søren Emil Kjær

Work in progress. Will be done by the 21th of February.

Abstract

Successful project managers apply a systematic way of thinking to ensure a successful outcome for their clients . This article will elaborate on this problem-solving approach by exploring the use of Gantt charts as a tool within the project managers toolbox. The Gantt chart, and its structure, is very much related to the concept of a project, which is defined as a set of activities which have a finite beginning and a finite end . Recently, the Gantt chart has undergone a major shift with the advent of software to easily create various charts becoming widely available. The purpose of this article is to provide an understanding of how Gantt charts are used in the 21st century, focusing specifically on their use by project managers. It will explore the fundamental information needed before implementing a Gantt chart and how to work with a Gantt chart once it is implemented. 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.

Fundamentals of the Gantt chart

The Gantt chart as a tool is one of the bedrocks of the project schedule management discipline . Developed by Henry Laurence Gantt in the second decade of the 20th century, the Gannt chart was initially used as a visual representation of the time schedule and progress of a given project . 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 scale is dependent on the individual project being analyzed and can therefore represent units such as years, months, days, and so forth. This can be derived from figure 1, which displays the straightforward design elements of the Gantt chart. In the example, the activities in the form of bars are displayed against the time axis in the chart. The progress of a project can be linked to the Gantt chart and is tracked with a vertical line (seen in figure 1) that represents the current date. Furthermore, milestones (represented in figure 1 by the star) can be implemented in the chart to show progress towards and expected completion of key project deliverables. Typical milestones include, the first test flight of a new airplane or finishing the foundation of a building. This allows the project manager to obtain a better overview of the project and its time schedule, therefore leveraging project schedule management techniques to ensure a higher probability of a successful outcome for the project.2 To ensure a Gantt chart has the appropriate information it is necessary to implement a framework such as the Work Breakdown Structure (WBS). The purpose of the WBS is to identify and segment all the different activities that define the entire project . By doing so, the Gantt chart becomes a more detailed and manageable chart of the entire project where constraints such as overlapping activities or 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 its graphical design leading it to be a very intuitive tool to use, hence why it is so widely used in the discipline of project schedule management around the world2. 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 straightforward to create Gantt charts using common software such as Microsoft Projects or Excel. This will be further elaborated on in the latter part of the article.

Application of the Gantt chart in practice

The Gantt chart is applicable in the majority of projects and is especially useful in projects with a continuous and/or repetitive workflow. This could include projects in manufacturing, construction, et cetera. To apply the Gantt chart there are some key steps that have to be performed in order for the chart to become useful for both the project and the project manager. It is important to note that as a dynamic tool, Gant Charts must be managed alongside the project they are tracking.

The five steps

The process to create an adequate Gantt chart is defined by the PMBOK Guide4 which contains the following five steps:

1. Define Activities.

2. Sequence Activities.

3. Estimate Activity Durations.

4. Develop Schedule.

5. Control Schedule.

The first step is to define the activities that make up the project. In this step it is advantageous to implement the aforementioned Work Breakdown Structure (WBS) to break down the project into manageable activities. As shown in figure 2, the WBS of building a house can quickly become a complex project with many different activities that each need robust planning. If done correctly, this step should allow the project manager to get a complete overview of the entire project and its constituent activities2. 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 imperative to know the order in which the different activities must be performed. Therefore, the dependencies of the activities must be clarified.

There are 4 major types of dependencies within a Gantt chart2:

Finish-to-start (FS): Activity a must finish before activity b can begin. Ex: 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. Ex: The electrician pulled all the wiring in the wall framing (Activity A). He only needs to put up the electrical outlet plugs to finish. Before that is possible, the carpenter must put up the remaining part of the wall (Activity B).

Finish-to-finish (FF): Activity a must finish before activity b can finish. Ex: the carpenter from before is now done putting up the walls (Activity A). The painter has been painting the walls as the carpenter finished them (Activity B). 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, must begin putting up the walls (Activity A), before the painter can begin painting them (Activity B).

The 4 types of dependencies are shown in figure 3.

Lead & Lag time

Alongside dependencies, the Lead and Lag times are crucial factors to account for when considering project schedule management.4

Lead time: Building in Lead Time is an optimization technique 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 referring to the overlap in activities. As shown in figure 4, the activities are being performed mostly concurrently and therefore saving time. 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 is able to begin their 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: Lag time is a project constraint that describes the required time in between certain activities. For the lag time to occur there has to be a dependency between the activities4. So that activity b cannot begin before activity a is finished. It is impossible to get through a project without lag time, but a crucial goal of project schedule management is to reduce lag time as much as possible. Figure 4 aims to show the visual representation of lag time. An example of lag time is found in laying the concrete foundation of a building. Once the concrete is poured, the project has to wait on the concrete to dry and develop sufficient strength so that work can continue. This required pause on activity 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 a given project and plan around them to reduce 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, their dependencies, and individual lead and lag times – a complete overview of the project is created. To ensure that the Gantt chart is robust and can withstand changes in the project, it is necessary to introduce Float. Float works as slack in the schedule and its main purpose is to create a feasible time frame for the individual activities to occur. The float number represents the amount of time an activity is able to be delayed without it impacting subsequent activities7. For example, an activity that is set to take 5 days, could be allocated a float consisting of 2 days. The total time allocated for this activity is 7 days, allowing for a buffer of 2 days in case of delays. By implementing float in the entire Gantt chart a form of resiliency is created in the overall project. This will work as a buffer for the chart and give the project manager room to maneuver and still keep the project on time.

Afterwards the project manager is able to define key milestones. While working through the above steps, the project manager is able to derive the critical activities in accordance with the Critical Path Method (CPM). The CPM provides a framework for outlining the mission 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 preceding activity is finished8. The knowledge of the CP allows the project manager to navigate in the project and ensure that the critical activities are managed.

The fourth step is to develop the schedule, which is done by utilizing the knowledge obtained in the previous steps. It is in this step that the project managers have to decide on what format the Gantt chart must be presented in. As previously mentioned in the article, the technological advances in our modern-day society have created a wide selection of software to choose from. The most basic form of rendering a Gantt chart is done by using Microsoft Excel. There are multiple templates available online which enable the project manager to insert all the data into Excel and manage it manually. While quick to get initially created, in the case of a change in the project the adjustments have to be done manually. Due to that, Excel templates can only be recommended for simple projects. A more useful tool for rendering Gantt charts is Microsoft Projects . This software is specifically designed to handle large sums of information in the form of activities and also manage the different dependencies between the activities. This means that prompt changes in the schedule will be accounted for without requiring manual intervention from the project manager. By implementing a thoroughly planned Gantt chart with Microsoft Projects, the project manager will free up a substantial amount of time. This software is widely used and considered as a baseline for rendering Gantt charts. Combining the above information with useful software will enable the project manager to control the schedule.

The fifth step is defined by the Gantt chart being completed. The controlling phase can begin4. This is where the managing of the project becomes reality. Managing will typically consist of administering the schedule, budget, resources, and quality of a project. Since the Gantt chart functions as the schedule itself, the quality of the output is based on the allocation of resources (time and money). Therefore, it is important to allocate adequate resources to each individual activity. The amount of resources should be linked with the time consumption of each activity and doing this allows the possibility of reworking your chart over the course of the project. The Gantt chart only takes into account time and it is the only resource that can be adjusted effectively on the chat. This time basis provides the option of managing the Gantt chart with schedule compression techniques4. These techniques allow the project manager to adapt the Gantt chart to the coming obstacles during the project.

There are 2 major techniques.

Crashing & Fast tracking

Crashing: This relates to the strategy of adding resources to a specific activity to decrease the time consumption of said activity. This could be in the form of working overtime, assigning more workers et cetera. This strategy 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 strategy 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 and in others it would be catastrophic to overlap activities. By introducing fast tracking, the total float of the project is significantly reduced. Fast tracking increases the risk of the project since activities are compressed and there is less room for error in the individual activities. If an error occurs, it will set back multiple activities due to the overlap fast tracking introduces. Alongside this higher risk, the cost will also increase with the amount of workers going up. .

Figure 5 provides a visual representation of the schedule compression strategy.

Limitations

The Gantt chart has some important factors to recognize and account for when working with the tool. The main limitation is the fact that the Gantt chart does not take into account the location of the activity. This means that the actual location of the activity being done is unknown to the chart. This is especially challenging when working with a project where multiple activities are occurring at different locations. A good example of this are construction projects. When constructing a large building, there will be parallel work being done in multiple locations at the same time. However, this work can only be displayed as a single bar in the Gantt chart. Recently, there has been a shift towards using the more nuanced Location-based scheduling (LBS) tool to hinder this complication . This tool is a more advanced form of Gantt chart where the locations are taken into consideration. Instead of displaying bars it is displaying lines – for further information about this see the annotated bibliography or visit www.Exigo.dk which is a consultant company specialized in this field of work.

In line with the location of the activities there is another fundamental limitation to the Gantt chart. Activities are displayed as bars with respect to one resource, time. One bar can represent 5 days and need 20 workers to complete that specific activity, whereas another bar can represent 5 days but only need 2 workers to complete that activity. This is a distinct limitation since the Gantt chart cannot display the amount of resources in a dynamic way. It is therefore highly important the project manager has a good understanding of the amount of resources being utilized in the different component activities. Which is also why this article emphasizes on allocating resources as one of the 5 steps to create a robust Gantt chart. Another limitation of the Gantt chart is its relatively low level of complexity. The larger the project, the more activities and dependencies it contains. The Gantt chart is very useful as a tool for the project manager, but at a certain point where the chart can become too divorced from the actual project itself. This essentially means that it is difficult to digest the chart and because the chart is managed by human beings this is a limitation. Managing the chart can also become a limitation of the tool itself. A certain amount of skill is needed to be able to manage a complex chart in a software like Microsoft Projects9. Projects are liable to experience a lot of changes and these changes have to be incorporated into the chart. A tool which takes up the majority part of the project managers time without providing any value is not a valuable tool. As shown over the course of the article, there is a large amount of work done prior to creating the Gantt chart itself. It is critical that the WBS6 and other component steps are done with precision. Otherwise, the Gantt chart will not represent the project correctly and end up being of no use to the project manager. Put simply, the Gantt chart is a tool which provides a visual representation of a project. As with all tools, it cannot succeed in planning the project on its own . It is necessary to implement other project management tools and strategies in order to create a robust Gantt chart.

In conclusion, the Gantt chart is a strong tool for project schedule management. It is important to note that the chart has to serve a purpose to the entire project organization. The fact that the project manager alone understands the chart does not guarantee a favorable outcome. The main benefit of the Gantt chart is its ability to distribute information in an understandable way and it is imperative that all stakeholders in the project understand the chart. This ability to share information is the core of why the Gantt chart has remained a widely used project schedule management tool for over one hundred years2. The simple way of distributing information has its price and that is also the reason why the Gantt chart has its limitations. Using the Gantt chart in relation with other project management tools can create a rigid baseline for a project3. To have a clear overview of a project is crucial for a project manager. By knowing the limitations, there is a solid foundation to understanding when and where to implement the Gantt chart as a tool. Consider the Gantt chart as a useful starting point for analyzing, understanding and managing smaller projects with less complexity.

Annotated bibliography

Harvey Maylor, (2001), Beyond the Gantt Chart: Project Management Moving on, University of Bath.

Gunnar Lucko, Thaís Da C.L. Alves & Vanessa Lira Angelim, (2013), Challenges and opportunities for productivity improvement studies in linear, repetitive, and location-based scheduling, Department of Civil Engineering, Catholic University of America, Washington, DC, USA and Department of Civil, Construction and Environmental Engineering, San Diego State University, San Diego, USA and Integral Engenharia, Fortaleza, Brazil.

Gus Cicala, (2020), The Project Managers Guide to Microsoft Project 2019, Wilmington, DE, USA.

Allan D. Orr, (2004), Advanced Project Management: A Complete Guide to the Key Processes, Models and Techniques, Kogan Page Business Books.

Randal Wilson, (2014), A Comprehensive Guide to Project Management Schedule and Cost Control 1st edition, Pearson.

Alireza Rezai, (2015), Location Based Scheduling In The Form Of Flow Line and Its Comparison to Cpm/Bar Chart Scheduling, International Journal of Mechanical and Mechatronics Engineering, Vol.5