Real Concrete Estimating
I will start with basic knowledge of concrete construction for the new bees. No worries, If you don’t even know what a construction site looks like, don’t worry everybody starts somehow. Over the years you will learn them all.
In this course, we will calculate the volume of the concrete and the rebar’s weight will be placed.
First, we will start with old-school handwritten calculations then I will show you how to use excel spreadsheets to improve our speed.
The Best tool Haqq Takeoff , Online Screen Takeoff Software
As far as tools, All you need is an online screen takeoff software to make measurements.
It is very important to select good software Since we are the designer and developer of the Haqq Takeoff we refer you o use our software thought out this course.
Go to Haqq Takeoff pricing for the free version.
And for now, All we need to know is rebar weights per foot for the sizes in the table below.
|Bar Size||Weight (LBS/FT)|
Table 1.1 Rebar Sizes and Unit Weights (Unit weight = weight of 1′-0 )
Calculating Rebar Weight is Simple
In this paragraph, you will see how easy calculating rebar is.
Firstly, from table 1.1 you can find the weight of 1′-0″ long #5 Rebar (1.043 lbs/ft),
If you know the weight of 1′, you can figure the weight of any length.
Secondly, do the calculation ,
Count x Unit Weight x Length
1 x 10 ‘ long #5 Rebar weight would be 10 feet x 1.043 lbs/feet (table 1.1)= 10.43 lbs
1 x 20′ long #6 Rebar weight would be 20 feet x 1.502 lbs/foot(table 1.1) = 30.04 lbs
See it is easy,
However, You don’t need to force yourself to remember unit weights. After finishing a couple of takeoffs, you will remember them by heart.
And You don’t need to solve major math problems in this course, Simplicity is the key.
The Field Experience is the Key for Success
Thirdly and most importantly, try to get some field experience. See and try to understand how heavy is one tone. look around you and search for the weights of the heavy things around you. For example Weight of the car, weight of the refrigerator,.. etc.
Moreover, get the feeling of the weight. Go to a lumber yard, lift up 20′-0″ long #6 rebar and feel how heavy 30 lbs is.
So you don’t make simple mistakes. Especially when you start working in a new field, you are learning. You need to pay more attention to be able to avoid mistakes. For example, we have a 100 feet long,10 feet high, and 1′ thick wall with #5 12″ on center vertical rebar at each face. Our calculation will be as below
101 pieces: since 100 feet long you need to start with one at the beginning at 0.
#5 weight : 1.043 lbs
Length: In this case, the height of the wall is determining our length of 10′-0″
Multiplication : 2 , because rebar at Each Face ,
101 x 1.043 lbs/ feet x 10′-0″ x 2 = 2,106.86 lbs
When you using calculated if you mistakenly type 10.43 lbs instead of 1.043 lbs , you will be getting 10,534.3 lbs.
These types of mistakes can be caught by field experience only.
In Conclusion, If we can visualize the weight of the rebar we know what we are doing.
We Got Tips for Everything
No worries, I have some tips that can help you to avoid mistakes.
We know that Rebar goes with concrete. If there is concrete, then you can talk about rebar. So we can make a relation between these two.
If we go back to the above example, for 100 feet long x 10′ high x 1′ thick wall = 1,000 cubic feet / 27 = 37.03 cubic yard
Tip : Average Commercial Building Concrete gets 100 to 150 lbs of rebar per cubic yard
as a result , 37.03 cy of concrete may get rebar between 3700 lbs to 5,550 lbs
So we already know there could be a mistake if we get 10,000 lbs rebar for 10 cy of concrete.
Clock is ticking
Timing is very important in Estimating. Usually, there is a bid date and you have to finish your takeoff in that time frame. Especially in public bids, there is a time set for bid opening. if you are late, all your work will be wasted. That’s why we start right away.
We start estimating in the order of how you built the building. The first excavator excavates, then frame and pour footings, then walls, then gravel base for the slab, then slab on grade, then structural slabs, then stairs, and so on…
Written by Kamil Cabuk, MS
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