Jim explains that the third step in creating a scheduling network model or precedence diagram is to establish activity relationships. Jim illustrates this by drawing logic link lines between each activity on the scheduling network.
- A precedence network, or a precedence diagram, shows each of our activities as a node connected by a logic link line that shows the dependencies between those activities. Like I said, we need to run through this by hand, because most of the scheduling software used today uses the same concept of a precedence network, and it requires you to enter all of the same information in order to really leverage the features and generate a working useful schedule. So let's get started.
Let's use the table that we generated in the last segment to draw a simple diagram that represents the relationships we determine to exist between the activities. Let's start with the items we identified in our table as having no predecessors. These are the items we can start at the beginning of the job, and that was our site fence and our surveying activities. Our table shows these activities as predecessors to the clearing activities, so let's go ahead and put that node in and link to that.
Clearing was a predecessor to rough grading, so we'll add that node and link it to the clearing. And to create the entire network model for the project, you would just continue this process, adding and linking each activity. At times, the diagram is going to look like it does so far. It's going to be flat, and this is what happens when we have a bunch of sequential activities. Other times there will be branches in the network, as we bring in activities that can run simultaneously with each other.
Let's zoom ahead and look towards the end of the network. After I finish the concrete quartz, I added in an activity called cure concrete, because I want five days in the schedule that these concrete quartz are covered up and protected before anyone starts to work on top of them. During that time though, is when my stressing operations are scheduled, so you see both of these activities diagrammed parallel to each other. In the WBS table, if we go back and look at that, tensioning and cure concrete, both listed install concrete quartz as their IPA.
Moving through the table, you'll also see both of these activities listed as the IPA for the install light poles activities. As you continue, you can see that as you diagram activities with multiple IPAs or as multiple activities have the same IPA, the diagram starts to take on a more complex look, it's not as flat as it was when the activities were sequential. At this point let's have brief discussion on activity relationships and these link lines that we're drawing.
For our discussion here, we're going to assume all of these relationships that we've drawn so far are what we call finished to start relationships. This just means that an activity's predecessor has to finish before it can start, or if you want to turn that statement around and restate it, once an activity is finished, it's successor can begin. Again, this is called the finish to start relationship between activities, and when you're doing these calculations by hand, it makes it much easier to only use this finish to start, or FS type relationship.
Now in real life, there are activity relationships that can be better described as start to start, or finish to finish, or even start to finish. The use of these different types of relationships though, is really dependent on your computer software, and they're really all just different ways of organizing activities that overlap in some way, or that may have a delay of time between them. For our exercise here, as we continue, let's stick with finish to start. So I have to finish the grating before I start the concrete.
Once our network drawing is complete, you'll have moved from a table of activities and IPAs to a graphical representation of how each of the activities is linked. The next step in the process of scheduling is to assign a duration to each of these activities. Stick with me and let's discuss that step.
This course identifies the steps needed to develop a proper plan, and demonstrates how that plan is transformed into a construction schedule. Throughout the course, instructor Jim Rogers shares examples of his own successes and failures in the areas of construction planning and scheduling, so as to lend real-world context to the concepts he covers.
- Types of schedules
- Planning versus scheduling
- Work breakdown structure
- Developing a schedule
- Creating a network model
- Assigning durations, costs, and resources
- Identifying the critical path
- Letting the software do the calculations
- Checking and updating the schedule
- Scheduling's impact on productivity