Introduction to the Interfering Float

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Из курса от партнера Columbia University

Construction Scheduling

655 оценки

Columbia University

Construction Scheduling

655 оценки

Курс 2 из 4 — 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.

Из урока

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

Познакомьтесь с преподавателями

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

Let's take another example.

And in this example, we will go also through total float and

free float calculations quickly.

But, I want to advance in this example, and give you more of interpretation and

introduction to another type of a float other than the total and the free float.

If you notice I try to pump it up a little bit more congested

activities and this is what you guys worked on in the previous modules as well.

The first thing comes to my mind also when I look at that critical path that

we identified, the longest path in our project here and I highlighted for

you, in yellow, the total float and the free float, again, are 0s.

Now let's go with the two activities here, B and E and then we will go with D and G.

For activity B, the total float also is 4 minus 2 is equal 2.

And the free float for activity B is the minimum of the successors,

the early start between 7 and 11 which is 7 minus 7 equals 0.

For activity E, the total float is 9 minus 7,

2 and the free float 15 minus 13 equal 2.

Now for activity D and activity G.

Activity D, the total float will be 17 minus 5 or

14 minus 2 equal 12.

For activity D here and G,

let's calculate the total of float will be 14 minus 2 12.

And the free float for activity

D will be 11 minus 5 which will equal to 6.

Activity G here, the last activity we have,

the total float 17 minus 11 which equal to 6 or 19 minus 13.

And the free float for activity G will be 19,

the successor minus the L if finish which is

the 13 which will equal also to 6.

As I mentioned to you, I want to highlight this example to

dig deeper here a little bit about another type of float.

Before that, let's discuss with you

with the numbers to make it like slowly easier for you to understand it.

Let's discuss activity D here, in the example.

It has 12 days of total float, so

let's say, we delay activity D by two days,

we notice, this will not affect

the early start of the immediate successor which is activity G.

Because if two days delay, 5 plus 7, still we have the early stop for G is 11, so

if this is 7 you still have time and will not affect the successor,

and also because activity G, is what?

Is waiting also for activity C, to finish his,

because there is two predecessors for G and this will finish at 11,

this will start at 11, but, let's say,

if activity D got delayed by more than six days,

lets say by seven days.

In this case, activity D will finishes on day number 12.

And, let's repeat that again.

If activity D got delayed by more than six days,

let's say by seven days, so activity in this kind of activity,

will finishes on 12 day number 12, which is the early finish

of activity D which is 5 plus the 7 days delays which is equal to 12.

We will notice that activity,

G cannot start until day 12 instead of 11.

We have 7 days delays, 5 plus 7, 12.

This has to start early start at 11, and

now it will be pushed to start at the 12th.

And it will suppose to finish,

in day 14, activity G.

Because if you have it, the start day is 12, 12 plus 2,

you supposed to have this then 14 instead of 13.

And that will not delay activity I,

and the project finish date, so,

if we have this activity delayed by 7 days,

5 plus 7, the finish day will be 12.

It will push this one day so the finishing will be 14.

But the 14 is still will not intercept with the 19 here.

Activity I will define and

the finish date of the entire project will be still be okay.

The seven days delay for activity D only delayed Its successor

which is activity G but not the entire product finish dates.

On matter of fact, we can increase the delay

to 12 days without affecting the entire project and

just affecting the successor activity G, as we mentioned before the total float.

This is now a quick summary.

Now, we can divide the total float of activity D which is the 12 days,

into the six days that will not affect the early start

of the successor, in the successor in this example G.

And we call that what?

Free float.

The other six days in this case, we'll cause the delay to its successor G,

even though they will not delay the entire project.

That then we will call it, interfering float.

That's a quick definition of interfering float, or what is an interfering float?

To look at it from a different angle, and summarize it.

We must always realize, from all the three examples we went through already,

that the total float is greater than or

equal all the time, than the free float.

On another word I can say that the free

float is more restrictive than the total float.

The free float on matter of fact, is a part of the total float.

And that part of the total float, the free float,

will not affect the early start of the following activities.

The other part of the total float is called then the interfering float.

Mathematically, we can say the following.

We can say that,

total float will be equal

to that free float plus

the interfering float.

Or, that means that sorry,

interfering float, or interference float,

will be equal to the total float minus the free Float.

What's the interference float of activity?

D here would be 12- 6.

Will be 6 days.

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