Bar (Gantt) Charts - Construction Project Scheduling and Control - page 19

Data Date

Percent

As Planned

Complete

As Built

Remove Old Roof

100%

Replace Rotten Rafters 90%

80%

Install Sheathing 70%

60%

Install Felt

50%
40%

Install Shingles 30%

20%

Clean Up 10%

Days

123456789 0 1 2 3 4 5

Figure 2.6 Bar chart for replacement of an old roof, showing a comparison between the
percent complete of the planned (as-planned) activities (thin line) and that of the actual
(as-built) activities (thick line). The dashed line is an extrapolation of the actual curve.

ADVANTAGES OF BAR CHARTS
Bar charts have gained wide acceptance and popularity, mainly because of their simplic-
ity and ease of preparation and understanding. No “theory” or complicated calcula-
tions are involved. Anyone can understand them. They can be prepared anywhere with
just a pencil and paper. So, although bar charts can carry—or be loaded with—other
information, the user must be careful not to overload them and, thus, lose their main
advantage: simplicity.
Unlike networks, bar charts are time-scaled; that is, the length of a bar represent-
ing a certain activity is proportional to the duration of that activity. Just by looking at
the chart, you can get an idea of the duration of each activity and the entire project.
Another advantage of bar charts is that they particularly appeal to persons who do
not have a technical background. For example, some clients and upper-level managers
may better understand the plan for carrying out a construction project by looking at
a bar chart than by looking at a schematic of a logic network.
A final advantage of bar charts is the ability to roll up or roll down a schedule, on
the basis of either a specific activity code (e.g., area, phase, responsibility, or floor) or
the project's work breakdown structure (WBS) (explained in Chapter 4). For example,
if the schedule on the detailed level (say level 5) has 2,130 activities, the bar chart
can be rolled up to 342 activities (level 4) or to only 55 activities (level 3). Another
example is that in a schedule for a high-rise building, you can show the bars summa-
rized by floor, where all of the work on a floor is shown in one bar so that you can
show the 3,000+ activities in only 30-40 bars. This is a major reporting advantage,
because you can show the schedule in detail to the technical teams but “roll it up” to
a small number of major (summary) activities for executive management. Although
this roll-up/roll-down feature exists in logic networks, it is much clearer and simpler
in bar charts.