Determining Total Float and Free Float

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Do curso por Columbia University

Construction Scheduling

518 ratings

Columbia University

Construction Scheduling

518 ratings

Curso 2 de 4 em Specialization Construction Management

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, Precedence Diagrams, Activity on Arrow, PERT, Range Estimating, and linear project operations and the line of balance.

Na lição

Activity Floats

Professor Odeh introduces the types of floats in a construction project including; total float, free float, interfering float and independent float.

Types of Floats in a Construction Project9:48

Activity Floats9:37

Determining Total Float and Free Float6:31

Introduction to the Interfering Float9:18

Independent Float9:17

Conheça os instrutores

Ibrahim Odeh, Ph.D., MBA
Instructor, Department of Civil Engineering and Engineering Mechanics, Columbia University
Director of Research and Founder, Global Leaders in Construction Management

So let's take here another example, example number 2 which is also a network

diagram that we worked on together in the previous modules, where we developed

the relationships between the construction activities in the diagram here, and

we calculated all the forward pass calculations to find the early start and

the early finish of the activities and the backward pass calculations for

finding the late start and the late finish.

Having the same equations just as a reminder for

the Total Float and the Free Float, please go ahead and

try to calculate in this example the total float and the free float for

a minute before we go move forward with the solution.

What we have here, the Total Float and the Free Float.

As I explained from the previous examples for the critical activities, and

again I highlighted the critical activities in yellow,

would be then 0 for the Total Float and the the Free Float for A.

Activity B would be the same thing Total Float under Free float 0.

D and G will have the same Total Float and the Free Float equal 0.

If you would follow the equations of the Total Flow, that's simply state forward.

The Free Float also, you always look at the minimum start dates for

the critical activities, and this is a good example for activity B here.

It highlighted that the early start for the successors, it happened to become

also the same end start of 11, and the same for D as well.

Now let's look at activity E and compare it with your solution here.

The total float of activity E would be 14- 16 or 19- 16,

which is 3.

And the minimum of early start of the successor of activity E,

which will be 19 minus the early finish of activity E of 16,

that will give us also 3.

And for activity C here,

the total float will be 9- 4, 5.

And the free float of activity C, will be the minimum

between the early start of the successors, E and F.

The early start of E 11, the early start of F 9.

So we'll take the 9 minus the early finish of C which is 9 which is equal zero.

For activity F, we'll have the early start of the successor,

the only one successor which is G 19, the early start date for

it minus the 11 of early finish of F, that will give you an 8 of Free Float.

The Total Float will be 17- 9 which also will give you an 8.

So let's pause here after taking these two examples and

think together why is this important?

The calculations and to understand the Total Float and the Free Float and

knowing why it is important to have as a PM or construction manager the float.

As a construction manager, you will notice as the project progress,

you always want to pay attention to the floats of your project,

watch it so closely so it does not disappear.

Because if it disappear, it will cause the project or

the successor's activities to be delayed.

So, let's say one of the critical tasks, A,

B, D, or G here,

is not progressing as planned, or as you want it to be.

If adding additional resources to that task, to that critical activity,

would help moving it forward, then, exactly.

Then moving resources, the construction resources, maybe labors,

maybe machines, or maybe spending a little bit more money on it from

non-critical activities to that critical activity,

that anticipated some delays in it, might make sense.

So when you move or when you relocate construction

resources from the non-critical activities

to the construction critical activities.

Its duration will lengthen and I mean the duration for the non-critical activity.

Because there is less resources in that non-critical activity.

By placing the resources on the critical tasks, its duration will shorten.

Or, will come back to its previous planned duration.

Then we can see the impact on the float and determine if it is acceptable.

Now, here what we're teaching you.

We're teaching you the fundamentals and the theory.

Now in real world, your plan and the plans in your hand would

be on some project management software like Primavera P6.

And you can play around in several,

what I call a what if cases scenarios to determine the best

avenue of realigning the construction resources, or labors, or machines,

part of the resources before you actually make the changes permanently.

In this manner, we can then avoid any costly mistakes that can

end up having the entire project to be delayed.

So, this is a tip that I want you to think about it very carefully

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