The Critical Path Method (CPM) - Construction Project Scheduling and Control - page 53

start) of another activity. For example, you cannot place the concrete until the
formwork and reinforcement are erected. You cannot hang the drywall until
framing is done.
b. A resource constraint (or restriction) is when you can theoretically do two tasks
at the same time but you schedule one as a predecessor of the other because of
resource (labor, equipment) limitations.
Some practitioners refer to the preceding two types of relationships as
hard logic and soft logic , respectively. This terminology is scientifically suitable
because hard logic cannot be relaxed under any circumstances, whereas soft
logic can be relaxed if more resources are acquired.
c. There is another type of constraint: when an activity is under a subjective
restriction such as approval of an owner or a government agency, funding avail-
ability, or even workspace availability. In most cases, such a constraint can be
transformed into one of the two types previously discussed. Typically, a good
project schedule may only have a few constraints of this type, at most.
Tip Box 4.6
Have you included all activities, including those to be performed by “external parties?”
4. Draw the logic network, and perform the CPM calculations
If you are using a computer program, it will perform these functions for you, provided
that you have input the correct data. In this step, you will obtain the calculated finish
date of the project, the critical path, and the available float for all noncritical activi-
ties. It is important to check the input and the output and not to rely totally on the
computer.
In most construction projects, subcontractors are involved, and their input
regarding the schedule is important. The schedule is typically one topic discussed in
preconstruction meetings with the owner, the general contractor (GC), and major
subcontractors. Often, the GC provides an opportunity for the major subcontractors
to supply him or her with schedules for work so that he or she can incorporate them
into the master schedule. Alternatively, the GC may create the overall schedule based
on feedback from subcontractors and other involved parties. (The GC then has to
communicate the schedule to all participants and get their approval or acceptance of
their roles. This topic is discussed further in Chapter 10.)
Tip Box 4.7
Subcontractors' schedules must be compatible with the master schedule so they can
be integrated smoothly.