Precedence Networks - Construction Project Scheduling and Control - page 104

ii. The SS relationship (with no lag) means A can start just before B starts,
LS (A) = LS (B) − Lag = 0 − 0 = 0. LF = LS + Dur = 0 + 5 = 5, so the
late dates are (0, 5)
The first answer delays the completion of the project (by delaying
the start of B), so it is rejected. The second answer prevails.
3. Note that unlike in Chapter 4, the durations may not be equal to EF − ES or
LF − LS . Furthermore, all or some of the total float may be restricted. This will
be elaborated in the detailed approach (discussed subsequently). Total float is
always calculated by using this simple equation:
TF = LF − Dur − ES
Free float (FF) is calculated the same way as in Chapter 4 and is always less than
or equal to total float.
General Notes on the Simplistic Approach
Two points regarding the simplistic approach should be noted:
1. The position of the relationship arrows (i.e., from top or bottom of the same
side) is a matter of aesthetics and is left to the user's choice. It has nothing to do
with the choice of early or late dates. For example, the network of Figure 5.17
can be redrawn as shown in Figure 5.18.
2. We may have dangling activities in precedence diagrams. Dangling activities
are tied from one end only. In other words, dangling activities have either no
predecessors or no successors. As mentioned previously, we like to always start
the network with one activity (e.g., Notice to Proceed) and end it with one
activity (e.g., Final Completion). As an example of dangling activities, you may
have a Clear & Grub activity with an SS relationship to the next activity, Exca-
vation, with a 4-day lag (Figure 5.19). Nothing controls the end of the Clear
& Grub activity (other than the end of the project). In this case, the LF date
of the Clear & Grub activity is the end of the entire project. Another example
Figure 5.18 Figure 5.17 redrawn
Figure 5.19 Example of a dangling activity