Bar Charts (Gantt Charts)

Henry L. Gantt developed the concept of ‘Bar Chart’ sometime in the year 1919. It is also called as Gantt Chart or Time and Progress Chart. In this chart, two activities are co-ordinated. It is essentially a graphic presentation of program of procurement of materials and a time bound schedule of completion of the various elements/stages of the project. Horizontal bars represent time, while vertical bars represent jobs to be performed. The methods of scheduling the various activities of the project are also known as time and progress chart. This chart is still being used in many production control sections. It was basically used to depict the work to be done and the inter-relations among all the phases of work. It shows the co-ordination that has to be maintained between the various phases of each of the projects.

Features of a Gantt Chart

• It plans the future activities.

• It shows the progress of different operations.

•  It also shows the achievements till the date.

•  It represents the possible delays.

• It also represents the failure of the plan.

• If a cursor sliding indicator is used in the Gantt Chart, it shows the cumulative progress till any particular day.

• It is simple to prepare and interpret.

• Each item of the work (activity) can be shown separately.

• Modifications to the chart can be easily carried out.

In the chart each bar shows the number of days (time) required for completing an activity. In every project, various jobs are taken up simultaneously. Some of them are to be completed in preference, while the others to be followed. In the above figure, the job ‘B’ can be started only when the job ‘A’ is completed. In some cases bars run parallel. Time can be saved by starting more than one independent activity at the same time. This however, depends the nature of such activities and precise judgement on the part of the executing officer about the overlapping durations of the time element of the jobs. Here A, C and D are independent activities and they can be starts without waiting for the completion of any one of these activities. The final job ‘E’ constitutes the assembly of the jobs A, B, C, D.

The bar chart can list out various activities involved in the construction jobs, beginning with the preparation and finalization of the site. This is followed by the foundation, sub-structure, super structure, fittings, finishings and a host of other activities. The last activity is that of pulling out temporary structures, removal of construction machinery and cleaning of the site.

The sequence of activities depends upon the methods adopted for the construction. Some of the activities may be of critical nature.



Limitation of a Bar Chart

• Bar Chart cannot indicate interdependence of the various activities.

• The bar chart does not indicate the progress of work. It cannot therefore be used as a control device.

• It cannot reflect uncertainty or tolerances in the duration time estimated for the various activities.

Preparation of the construction schedule involves the following:

•  Identify the various activities.

• List out the various activities in a sequence.

• Estimate the volume of work from the drawings.

• Decide the time for each activity.

• Find out the dependency on other items of work.

Conventions commonly used in Bar Charts

Typical Bar Chart Schedule