Bar Charts

1. Principle of Bar Chart

In dealing with complex projects, a pictorial representation showing the various jobs to be done and the time and money they involve is generally helpful. One such pictorial chart, also known as the bar chart, was developed by Henry Gantt around 1900. Bar chart is also referred to as Gantt chart.

A bar chart consists of two coordinate axes, viz., one representing the time elapsed and the other representing the job or activities to be performed. The jobs are represented in the form of bars as shown in Fig. 31.1.

Figure 31.1 Bar chart

The beginning and end of each bar represent the time of start and time of finish of that activity. The length of the bar represents the time required for the completion of the job or activity.

In any project there may be some activities which are to be taken up simultaneously but may take different lengths of time for their completion (e.g., Activities A and C) and some activities have to be taken up only after the completion of some other activity (e.g., Activities A and B). There may also be some activities which are independent of all other activities (e.g., Activities D and E).

2. Example

Let us consider the steps involved in the construction of a factory shed. Major activities identified in the construction of a factory shed where machines are to be erected are presented in Table 31.1. The activities have been identified and arranged in logical sequence. At the factory site no water is available and is not feasible to get water from surrounding. Hence, a bore well has to be sunk before starting the actual construction. Hence, excavation of foundation and sinking of bore well may be started simultaneously. That is, at the end of one week, water will be available.

Table 31.1 Activities of construction of factory shed

Other activities succeed one after the other. These activities are shown in a bar chart in Fig.31.2, with the given data and given precedence/succedence relationships.

Figure 31.2 Bar chart for factory shed

As seen from the bar chart, the total time required for completion of the factory shed project is about 30 weeks.

3. Limitations of Bar Chart

Following are the limitations of a bar chart:

1. A bar chart can be successfully used only for small projects.
2. Bar charts can not be updated when there are many changes.
3. The progress of the project can not be assessed at different stages scientifically.
4. Bar charts do not equate time with cost. That is time-cost relationship can not be derived.
5. Delay in the work can not be deducted.
6. It does not clearly show the interdependencies between the various activities in the project.
7. It does not reflect the critical activities of the project.
8. Bar charts do not provide methods for optimising allocation of resources.