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Figure 9-22.—PDM network with total and free float calculations. | Up
Builder 3&2 Volume 01 - Construction manual for building structures | Next
Figure 9-26. Typical Precedence diagram for a 40-by-100 foot rigid-frame building. |
Figure 9-24.—Dependent activity.
Calculating the free float consists of subtracting
the earliest start (ES) date from the latest start (LS)
date, or:
Figure 9-22 is an example of an activity-on-node
precedence diagraming method (PDM) network
with total and free float calculations completed.
INDEPENDENT ACTIVITY.— An independent
activity is an activity that is not dependent upon
another activity to start. Activity 1, diagramed in
figure 9-23, is an example of an independent activity.
DEPENDENT ACTIVITY.— A dependent
activity is an activity that is dependent upon one or
more preceding activities being completed before it
can start. The relationship in figure 9-24 states that
the start of Activity 2 is dependent upon the finish of
Activity 1.
Frequently, an activity cannot start until two or
more activities have been completed. This appears in
the diagram as a merge or junction. In figure 9-25,
Activities 3 and 4 must be completed before the start
of Activity 5.
Earlier we mentioned a “burst” of activities. A
burst is similar to a merge. A burst exists when two
or more activities cannot be started until a third
activity is completed. In figure 9-24, when Activity 2
is finished, Activities 3 and 4 may start.
Advantages of Diagraming
Precedence networks are easy to draw because all
the activities can be placed on small cards, laid out on
a flat surface, and easily manipulated until a realistic
logic is achieved. It is also easy to show the interrela-
tionships and forward progress of the activities. Just
Figure 9-25.—Merge.
9-23
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