Relationship between total float free and independent

What is Float and How To Calculate Total Float?

relationship between total float free and independent

What are the differences between Total and Free float? logical relationships to show the sequence in which the activities are to be performed. Relationships. Durations. Interfering Float delay to the Early Start of some following activity. Independent. Float. (IndF). Amount by which an Applying Definitions. • Total Float. – B 2 days. • Free Float. – B 2 day. 1. 2. 3. 4. 5. 6. 7. 8. 9. Learners will discover the key project scheduling techniques and procedures including; how to create a network diagram, how to define the importance of the critical path in a project network, and defining project activities float. Also covered are the fundamentals of Bar Charts.

Finding out Late Start and Late Finish Using Backward Pass In the backward pass, you will start with the end activity node and traverse through backward till the start activity node in each path to find the late start and late finish for each of the activities in all the paths of the project. Activity D So let us start at the end activity of path1, which is activity D. And calculate the late start and late finish of activity D.

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Calculating Total Float or Float We already learned in the previous blog post on how to calculate float in a simple way. Now we will see how to calculate float using the early start, late start, early finish and late finish value, we just calculated. Also we have learned that the total float of the activities on the critical path is always equals to ZERO, by definition. That is why if you see the above completed network diagram, in the critical path the late finish and early finish are referring to the same number.

In the same way late start and early start are referring to the same number.

What is Float and How To Calculate Total Float?

Calculating Free Float Free float is different from total float. So free float not just considers that the project is on time, but also considers the successor activity is on time.

As free float of activity E is 1, indicating that the activity E can slip maximum by 1 day without impacting the timelines of it successor activity F. In the same way, free float of activity F is 9, indicating that the activity F has luxury or flexibility of slipping 9 days, without impacting the timelines of its successor activity D.

relationship between total float free and independent

In the above mentioned completed network diagram, you can observe that activity F any way have to wait, until activity C also finishes for activity D to start.

Conclusion This is really a long post, to cover various calculation such as float, total float, free float, early start, early finish, late start and late finish using the forward and backward pass. A project can also have negative float, which means the calculated completion date of the last activity is later than the targeted completion date established at the beginning of the project.

If activities that are not on the critical path have a difference between their early start date and their late start date, those activities can be delayed without affecting the project completion date. The float on those activities is called free float. John could start work on Wednesday, December Subtract the duration of each activity in each path to determine the latest date the activity could begin and still meet the project completion date.

relationship between total float free and independent

Resource calendars must be considered in the backward pass as well as the forward pass. To calculate late start dates, begin with the project completion milestone and assign that date as the finish date of its predecessor activities. Follow these steps to calculate the late start dates of predecessor activities, assuming finish-start relationships: Subtract the lag time or add the lead time to the late finish date.

Refer to the resource calendar s that applies to the people and equipment necessary for the activity, and subtract the number of off days that the activity would span on those calendars.

relationship between total float free and independent

Assign the calculated date as the late start date of the predecessor activity. The difference between the early start date and the late start date for activities on the critical path is usually the same as the total float, unless the activities are affected by the resource calendars differently in the forward and backward pass. For example, if a piece of key equipment is only available for a few days, activities that depend on it have the same start and finish dates in the forward and backward passes.

KEY TAKEAWAYS To calculate total project float, begin at the start date and add the duration of each activity in each possible path through the network diagram, including nonworking days from the resource calendars, to determine the early project end date. Relationships that are not FS or have Lags do not lend themselves to traditional crashing methods.

Table 3 lists the activities found in Figure 2 with their data needed for crashing. While the activities listed in Tables 1 and 2 are on the critical path only two activities are entirely critical, Activities A and D.

Reducing the duration of B does not affect the total project duration because the relationship from Activity C to Activity B has a greater effect than that of Activity A to Activity B.

relationship between total float free and independent

The total project duration will not be reduced because of its constraint from Activity I. Thus it is recommended to see if the lag from Activity I can be revised.

Joe Lukas Explains Total and Free Float

It cannot be crashed. However it will have more total float if it is crashed.

What Is Float And How To Calculate Total & Free Float?

However, because Activity B has a constraint enforced by Activity C to the finish date of Activity B, the project duration will not be affected. Reducing the duration of Activity C may or may not be beneficial to the project. Reducing its duration can affect the finish date of Activity D which happens to be critical. Otherwise it may not affect the project duration. Another example of the effects of non FS relationships is seen in Figure 3which is a portion of the logic diagram for placing a footing.

The inspection needs to be completed on Day 13, however, it can start as early as Day In other words, according to the logic, there needs to be an inspection as the rebar and formwork is being placed, there also needs to be an inspection done when the Footing concrete is placed. This problem would best be solved by splitting the inspection activity into two separate activities to take care of both the needs spelled out by the logic.

relationship between total float free and independent

This example does serve to demonstrate some of the issues that can occur with the use of lags and non-finish-to-start relationships to take care of some logic needs of a project.

As shown in Figure 2some activities in the critical paths are critical based on either their start date or finish date. Conventional crashing guidelines cannot be applied to reduce the project duration because it assumes the whole activity is critical [2,12].

What Is Float And How To Calculate Total & Free Float?

Based on the guideline, reduction in activity duration on the critical path causes automatic reduction in schedule time. However, if either only the start date or finish date is critical, crashing a critical activity does not cause an automatic duration reduction in the schedule as.

When this is the case, especially when STF of an activity is critical, a revision of relationships to the activity is suggested prior to crashing the activity. The following additional suggestions should be considered: Suggestions When constraints are used in a project, this creates the need to use non FS relationships and lags and leads. This leads to two observations. Secondly, multiple relationships between activities can also create these differences.

In such cases, it is recommended these be done by hand and not be dependent on the scheduling software to tell if the start date, finish date, or entire activity is critical.

Secondly, before choosing a method to crash the schedule with an activity with two total floats it must be determined if the start date is critical or the finish date. If the start date is critical the predecessors need to be looked at to determine if the relationship or the activity is critical. In the event of two total floats the relationship should be crashed.