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 forms.
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 before it.
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!Continue Reading