DEVELOPING A GANTT CHART OR A BAR CHART
PRACTICE PROBLEM:
Identify key short-commings of the presented Bar Chart
COARSE UNITS
Most project plans can be estimated with days as the unit of
time, but in this case the unit is too coarse and half-days would have
been better. For example, it will not take a whole day to make and
position the formwork for the concrete base. Half-days are often
convenient units for small projects, especially where there are five
working days in a week, because a week is then ten units.
Another fault with the bar chart in Figure 2.2 is that it does not
show weekend days. Although most jobs will not have any activity
during Saturdays and Sundays, on this project paint will continue to
dry over a weekend and concrete will continue to cure. So the chart
should include Saturdays and Sundays for those reasons. When the
chart is drawn by hand, the contractor can use his or her mental
powers to determine which activities will run through weekends.
When, as in later chapters of this book, a computer is used, special
steps must be taken to instruct the computer as to which activities
run five days per week and which can take six or seven days.
There is a fundamental flaw of logic in this first bar chart
attempt. All jobs are shown in a simple sequential series. Broadly,
the jobs do follow the sequence that construction would need on site
but some of these jobs could take place simultaneously (provided
enough workers are on hand). To take just one example, the
concrete for the car hard standing area could be poured at the same
time as the workshop base – provided we have not forgotten to dig
the soakaway first.
So, bar charts are excellent for displaying working schedules but
they are by no means the best way of working out and showing the
logic of how the start of one job is dependent on the finish of
another. For very small projects this can be overcome to some
extent by the use of linked bar charts.
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