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.
Types of Floats in a Construction Project
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Из курса от партнера Columbia University
Construction Scheduling
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Activity Floats
Professor Odeh introduces the types of floats in a construction project including; total float, free float, interfering float and independent float.
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Ibrahim Odeh, Ph.D., MBAInstructor, Department of Civil Engineering and Engineering Mechanics, Columbia University
Director of Research and Founder, Global Leaders in Construction Management
I will be covering in this module the construction floats and
the type of floats that we do have in our construction projects.
There are several types of Floats that we used in the construction.
Mostly, what we used most of the time the first two types of
floats which is the total float and the free float.
However, you might be while you are studying either in a textbook or
reading couple of papers, you might find another two definitions referring to
as interfering float or interference float and
the independent float which I will also touch base on them just quickly,
so as you have an idea about all these types of floats and what they mean.
So let's start with the first one.
The total float and it is actually what we are aware of in our industry and
it is commonly used name as or referred to as the float.
So if you hear something or you hear someone say, okay,
what's the float of a specific activity or your project,
that's the first tool as the Total Float by default.
And the Total Float is also known as the slack or
the buffer of a specific construction task or
construction activity, and the slack or
float provide the flexibility in the project schedule.
And when leveraged properly, construction managers and
the PM on the project can shift activities and construction resources.
To meet the project objectives and
properties which we will be talking about it for later, as an example.
So for definition on total float I like to use this definition which is.
The total amount of time that is specific construction activity that say I,
the starting date or the finishing date of that activity.
Can be delayed without affecting the overall completion
of the construction project itself or
to cause delay in the project's finish date.
Mathematically speaking the total flow out of activity A or
Y or X or Z is the late start
of that activity minus the earliest start of that
activity or sometimes which will give you the same answer.
The total float of the specific activity will be the late finish of
that specific activity minus early finish of that activity.
So I want you to think based on this definition here and
the mathematical equation we gave for the Total Float.
On what is the Total Float,
of any critical activity.
Also, think about the following question.
If an activity that delayed from
it's early start, by more than it's total float.
What could happen?
So 2 questions.
What is the total float of any critical activity?
And if an activity got delayed from its early start by more than the total float,
what could happen here?
So the answer for that is, the total float of a critical activity,
will be always zero.
If you remember, when we covered the forward and
the backward task calculations.
We highlighted that the latest start and
the early start, they are equal for critical activities.
And the late finish as well as the early finish.
The same, they are equal so
the total float is also zero if it is a critical activity.
And we will go through a couple of examples shortly.
The other question I ask you if an activity got delayed
from its early start for more than its total float,
it will affect in this case the duration,
or the finish date of the entire project
that's why by definition we said that the total flow is the maximum number.
Number of days that an activity can be delayed without
affecting the finish time or
date of the entire construction project that you are working at.
That's for a total float.
The free float on the other hand is
the definition, the amount of time that an activity.
Let's say activity A or I can be delayed without delaying.
The early start of any immediately or
immediate following activities, the successors.
Before I go to the mathematical, I want to add to that is that free float in this
case of any activity, is the difference between That
minimum early start date of its successors
as we can see here, and its own early finish date.
So, when we say the finish, the free float of activity,
I plus one refers to the successor at
the successors' activities that following I.
You find the minimum early start of all these successors and
you subtract it from the early finished of the activity
itself that I'm trying to find free float to.
So the free float i'm finding it,
calculating it to study how late or
how buffer time I have the duration find my have.
That I can delay it without affecting
the immediate successors of that specific activity.
So if I want to do kind of a quick comparison between both
the Total Float and Free Float, because there is always questions between both.
The Total Float more focused on the project finish date.
The free float focusing on the early start date of any successor activity.
This is one, this is two different things.
Okay?
And an assumption here, we're highlighting for the Total Float and
the Free Float that the Total Float for activity A,
let's say, it shows the following, all activities
predecessors to the activity you are calculating the total float for
began as early as possible, in their early start dates.
All the predecessors and
all the successors' activities began as late as possible.
That's an assumption that highlighted for the total float.
Because it's the most relaxed float we have between all types of floats.
The free float is more restrict.
The assumption for it also shows that all predecessors and
all successors of activity A or
the activity you're trying to find the free float for or calculate it.
Begin as early as possible.
In the early start and the activity itself, activity A,
ends as early as possible
at early finish, and we will
talk in more details through examples on numbers to better understand that.
So, if I want to sum it up from this slide, the total float
Is the amount of time that an activity can be delayed
from its early start date without delaying the project finish date.
The free flow Is the amount
of time that an activity can be delayed without delaying
the early start date of any successive activity.
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