Precedence Networks - Construction Project Scheduling and Control - page 117

With both solutions, we were able to get the earlier project finish date (12 days)
as compared to the later date (14 days) with the contiguous activities option.
Tip Box 5.2
While “interruptible activities” may be an option, it is simpler to split these activities
into two or more contiguous ones.
THE CRITICAL PATH REVISITED
In Chapter 4, we defined the critical path as the longest continuous path from start
to finish, taking in consideration all time-consuming and time-impacting factors. The
definition still holds without any change, however, its application in a network with
some or all interruptible activities has to be more careful, as the critical path will
include part of (start or finish) some activities. For example in Figure 5.15, the crit-
ical path is: Activity A, FF relationship to end of activity B, and FF relationship to
end of activity C. In Figure 5.17, it is start of activity A, SS relationship to activity
B, all of activity B, the FF relationship to end of activity C. In Figure 5.23 it is: Start
of activity A + SS lag (A-C) + activity C + FF lag (C-E) + Finish of activity E +
activity G.
In Figure 5.24 (interruptible activities with double-restricted float), there are two
critical paths: Path 1: Start of activity A, SS relationship to activity B with 2-day lag,
SS relationship to activity C with 3-day lag, all of activity C. Path 2: All of activity A,
FF relationship to activity B, FF relationship to activity C.
So basically, the definition of Chapter 4 holds with the note that the SS + FF
combination relationship may produce two critical paths.
FINAL DISCUSSION
Four final points should be considered:
1. The subject of precedence diagrams can be somewhat complicated. It is easy
for someone in the field to use the “sour grapes” excuse and say, “Who uses
these things anyway?” There is nothing wrong with making assumptions that
simplify our life. However, if these simplifications mean avoiding a subject
that we perceive as complicated or unfamiliar to us, we may be missing some-
thing important. Understanding the nature of relationships among activities
is extremely important. Making the assumption of interruptible or contiguous
activities is also important. It can result in a difference of several days in the