schedule is the proper, logical sequence of activities
and good realistic durations. Performing the forward
and backward pass will identify the critical path. The
critical path gives you a list of milestones (activity
completion dates) that must be met. If these milestones
are met, the project will be on track and finished by
the scheduled completion date.
LEVEL II ROUGHS. As the construction
schedule unfolds, a commitment of resources (labor
and equipment) from several different companies is
required to ensure you can maintain the schedule.
Rough Level II schedules coordinate the planning
effort between companies and ensure that no particular
company or rating is overtasked during any phase of
the deployment. Good coordination in the beginning
is less painful than a major overhaul later. Having
determined the sequence and approximate duration of
each master activity, you can construct a Level II bar
chart. Each project will have a Level II. The OPS
officers and the company commanders typically track
projects using a Level II. Bar charts are covered in
greater detail later in this chapter.
LOGIC NETWORK. The logic network, also
refereed to as precedence diagraming, is the basic
management tool for controlling, monitoring, and
distributing all resources that are directly related to
time. The logic network at the planning stage is a pure
dependency diagram. All activities are drawn in the
order in which they must be accomplished without
regard to particular construction preference. One of
the major uses of the logic network during the
planning stage is to indicate all activities that must be
accomplished to complete a particular project (fig.
2-31). The individual network activities should be
well-defined elements of work within the project and
should be normally limited to a single rating. As a
general rule, an activity should be created for any
function that consumes or uses direct labor resources.
Resources (manpower, equipment, tools, or materials)
MUST be tied directly to the CAS sheet and network.
The crew leader constructs a logic network,
showing the sequence of construction activities from
the first to the last and the dependencies between
activities. Make sure no items of work are left out. It
is important that you do the logic network when
breaking the project down into construction activities.
You do not yet have construction activity durations, so
you are only concerned about the sequence of work.
Each construction activity is represented by an activity
block. In the network shown in figure 2-31, activities
0311, 0321, and 0211 cannot start until activity 0151
is finished. Activity 0312 cannot start until 0311 and
0211 are finished, and activity 0331 cannot start until
all previous activities are finished.
BASIC SCHEDULE (FORWARD AND
BACKWARD PASS). Using the crew sizes, now
you can determine the construction activity durations.
Go back to the logic diagram and insert the durations
to determine the basic schedule. Practice with the
example here and those included later. Some minor
revisions may be required to the basic schedule (see
resource leveling) before setting the final schedule.
On the precedence network, you will need to insert
into an activity block the activity number, the
description, and the duration for each activity.
The first step in determining the basic schedule is
to do a forward pass. The forward pass gives you the
total duration of your project. You start with the very
first activity and plug in a zero for its early start date.
Then add the duration to the early start date to get the
early finish date. The early finish date for an activity
becomes the early start date for the next activity.
Notice that activity 0312 in figure 2-31 has two
preceding activities (0211 and 0311) and you chose
the larger of the early finish dates (11 vice 10).
Remember to add any lag time between the activities.
Lag or delay times are mandatory wait times
between activities. A common example is concrete
cure times. Cure times require you to wait several days
to weeks after placing concrete before you strip the
Early Start + Duration = Early Finish
Early Finish + Lag (if any)= Early Start (next activity)
Look at the network in figure 2-31; the early start
and finish dates for an activity depend on the number
and duration of the activities that have to be done
The next step in determining the basic schedule is
a backward pass. The backward pass determines
your critical path. You start by taking the early finish
date for the last activity and making it the late finish
for the last activity. For each activity, you subtract the
duration from the late finish date to get the late start
date. The late start date will become the late finish date
for the preceding activity. Notice that activity 0211 in
figure 2-31 has two follow-on activities and you took
the smaller of the late starts (11 vice 12). Follow the
equations shown through the network in figure 2-31.
For any activity where the early start is the same as the
late start and the early finish is the same as the late
finish, that activity is critical!