Civil Engineering Reference
In-Depth Information
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The preceding three practices are all based on the assumption that the logic
cannot be changed. In reality, the relationships of some activities can be relaxed
somewhat. The most common reason for this is when, for example, activity B
requires only a portion of activity A to be finished before it can start. Project
managers tend to assign finish-to-start (FS) relationships for all types of cases.
A more in-depth inspection of the schedule by the scheduler and the project
manager may reveal some of these cases. Changing the FS relationship to an SS
relationship (possibly with a lag) may open the schedule a bit by giving some
activities more float and, hence, more flexibility. In Figure 6.13, the two-activity
setup in part (a) takes 18 days, whereas the one in part (b) takes only 11 days.
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Make some activities interruptible. To the author's best knowledge, commer-
cial software scheduling programs do not give the user the option of having
certain (but not all) activities be interruptible and then allowing the program to
interrupt (split) them in the optimum way from a resource-leveling viewpoint.
However, some programs allow manual interruption (pause, resume). As a rem-
edy (discussed in Chapter 5), you can split the activity into two or more activities
if this interruption was planned, or “pause and resume” if it was not planned.
Oracle Primavera P6 allows the user to manually pause and resume activities. In
this case, the interrupted activity does not show as a group of small bars. Rather,
it shows as one long bar that includes work and stoppage/pause periods (e.g.,
in Figure 6.10, the bars for activities F, G, and K stretch throughout their dura-
tions). The actual duration will be distributed within the bar without violating
logic constraints (such as finishing E, F, or G before finishing C).
Tip Box 6.3
Splitting activities (those that can be performed in different batches) may help the
scheduler in the resource-leveling effort.
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In Oracle Primavera P6, the resources (or budget) are distributed evenly
throughout the duration of the activity. You may change this by assigning
another distribution (e.g., triangular, normal, bell-shaped curve). You may
define your own type of distribution by dividing the resource (or budget) into
11 increments throughout the duration of the activity. Increment 1 is usually
3
A
10
B
8
A
10
B
8
(a)
(b)
Figure 6.13 The effect of changing (a) an FS (finish-to-start) relationship to (b) an SS
(start-to-start) relationship: a decrease in duration from 18 days to 11 days
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