Schedule Updating and Project Control - Construction Project Scheduling and Control - page 182

These two scenarios are not mutually exclusive. They can occur concurrently. The
project manager must find solutions to bring such activities back on schedule and
to eliminate any negative float. The project manager may meet with the scheduler
to discuss some “what-if” scenarios in order to work out or suggest a solution to
the problem. The meeting may include the subcontractors (those whose activities are
involved) so that their consent can be obtained for any proposed recovery plan (see the
“Recovery Schedules” section in Chapter 8). However, we must caution against the
usual “blame the contractor” attitude and consider the possibility that the contractor
may not be at fault for the negative float. The delay may have been caused by the
owner, unforeseen conditions, force majeure , or another situation that is beyond the
contractor's responsibility.

Change in the Critical Path

Sometimes, the critical path changes after an update. This happens if any of the fol-
lowing occurs:

• The critical path gets shortened if either an activity (or activities) on the critical
path takes less time than originally planned or an activity on the critical path is
deleted so that the second longest path takes over.
• A noncritical (usually near-critical) path becomes longer if either an activity (or
activities) on it takes more time than originally planned or an activity is added
to the path so that it becomes the longest path.

The project management team must then shift its attention to the new critical
path and determine why it has become critical (particularly in the latter case). For this
reason, it is wise to always inspect near-critical activities along with critical activities.
In almost every scheduling software package, you can run a filter that selects only
activities with a TF less than a value set by the user. In the absence of a negative
float, a number between 3 and 5 is suggested for the filter. Any activity with TF 3

is practically critical and has a better chance than others of becoming critical during
construction.

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Float after the Update

For completed activities, float “expires”; that is, it no longer stays available to that
activity. It may be “inherited” by succeeding activities. For example, if we examine
activities D, H, L, and M in Example 7.1:

• Before the update, they had TF = 6

6, respectively. Remember that
total float is a path float, so the total float of activity D is part of the total float
of activity H.
• After the update, the total float of activity D expired. As for activity H, it lost
4 days of its float (it had not yet started, even though it had an ES = 6, and

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