Class 109: Gantt Charts

WHAT IS A GANTT CHART?

A Gantt Chart is a type of bar chart that provides a graphical representation of a project that includes the activities that make up the project. The activities, represented as bars, are time scaled and show activity ID, description, duration, start and finish dates, and an overall sequencing of the flow of work.¹

Example of a Gantt Chart:

The example above shows a typical construction schedule. The left half of the schedule identifies important information in the WBS; information such as start and finish dates, activity durations and total float for each activity. The right half of the schedule displays the Gantt chart. The rectangular horizontal bars represent activities. The red bars identify forecasted critical activities, the green bars identify forecasted activities with positive float, and the blue bars identify activities that have been completed. The diamonds are milestones and typically represent important contractual items, such as substantial completion. The yellow bars and diamonds identify dates from the attached baseline schedule. The varying lengths represent the activity durations. The activity bars are logically tied to other activities or milestones. 

Additionally, a time scale is applied to the Gantt Chart, which provides the viewer a sense of the amount of work remaining at any point in time and can help prioritize completion of the work.  With activity names noted beside the activity bars, a simplistic view allows for a quick and easy review of the schedule. 

What are some other reasons to have a Gantt chart?

Gantt charts can help identify how many resources are required to complete the project.  For example, overlapping bars indicate activities that will be executed at the same time and will require multiple resources to complete. 

Gantt charts can also be used to identify various risks in execution. For example, activities with very long durations, identified in the Gantt chart by long uninterrupted horizontal bars, are likely made up of multiple smaller activities that are logically tied but not broken out in the schedule.  If any of the smaller activities are delayed, the larger bar’s duration is extended. Since the activities are summarized by one long bar rather than shorter specific activities, it would be difficult to identify the specific event causing delay within the summary activity. From reviewing the Gantt chart and noticing the summary activity, project schedulers can break out the summary activity into more detail and avoid future issues with analyzing project delays.

Gantt Chart Summary:

1.      Gantt charts graphically represent a construction schedule.

2.      Gantt charts make it easier to identify schedule risks and can help create a mitigation strategy.

Key Terms:

Construction Schedule - a comprehensive and realistic plan that represents the specific activities, reasonable duration for the activities, and the planned sequence of work for the project

  Logic - Relationship describing the interdependency of starts and finishes between activities or events

Resources:

1. AACE International Recommended Practice.  91-R16: Schedule Development AACE International Recommended Practice https://web.aacei.org/docs/default-source/vl-papers/22776.pdf