In the bar chart method, works are first
split into activities. These activities are then listed in the order of
construction priorities, generally on the left hand side column, while the time
scale is plotted horizontally on the top and/or bottom of the chart. The bar
against each activity represents its schedule of work. The start of the bar
marks the commencement of the activity and the end of the bar, its completion.
The length of the bar on the calendar scale represents the duration of the
activity data and the rectangular shape bar represents the activity schedule.
The time base of bar charts-and, for that
matter, all scheduling techniques is the project calendar. Generally, this
calendar covers a bar or tabulated format, a project’s life span from the date
it started to the date of its final completion. It specifies the dates when the
activities can be scheduled for execution. It shows all calendar months, weeks,
working days, weekend non-working days and holidays. The calendar weeks may
have the standard five or six working days. The detailed calendar also
highlights the various non-working days such as the weekends and national and
other holidays. The project calendar and its parts are invariably, represented
in a bar format.
The chart can be vertically divided into
three divisions. The left division group activities are listed in the sequence
of their execution. The central portion contains the data of activities. The
right division depicts the calendar and the schedule of activities.
Graphically, the three vertical segments of a bar chart can be arranged in the
following ways:
a. Activity description, data and calendar.
This is commonly adopted sequence.
b. Activity description and calendar. This is
used where data is omitted.
c. Calendar with activity (or work package or
task) only with description written inside or at the end of the bar. It is
particularly useful for making a schedule for a large project.
d. Data followed by calendar with description
inside or at the end of the bar. This facilitates scheduling of long duration
projects.
Bar charts are easy to plot, comprehend
and communicate, and are most appropriate for presentation of schedules.
However, as planning technique, the bar chart is not suitable for complex
projects due to the following reasons:
a. It does not reflect the relationship
between various activities which are common feature of all complex projects.
b. It cannot identify and highlight the
emerging critical tasks needing special attention for preventing schedule
slippages, time overruns, and other bottlenecks.
c. In complex projects, time durations are
often educated guesses. Any change in schedule or time duration would require a
redrawing of the multi-task bar chart schedule.
Thus, it can be said that the bar chart
format is most useful for presentation of schedules, but as a planning
technique, it is not suitable for scheduling of complex projects.
