Answer by Santosh Kulkarni:
Great question .
May be I can throw some light on this.
There are 3 methods .
Each method has its own advantages and disadvantages.
Let us see them in brief.
RCC comprises of concrete and steel bars.
Concrete is strong in compression but weak in tension .
Therefore , steel bars when provided in RCC , give resistance against the tensile stresses.
The RCC drawings give each detail of the Reinforcement .
However, finding out the exact weight of the steel bars is a job of the construction engineer. In big organizations , this job is entrusted to the Quantity Surveyor.
In smaller construction companies, this is done by the Site engineer.
Why weight of Steel bars is needed ?
- For finding out how much quantity of steel bars we need to buy for the work.
- For keeping an account of how much steel bars have been actually consumed in the RCC work.
- For giving a reconciliation to the client regarding the steel bars issued and consumed.
- For making a bill of the steel bars
Method 01 :
Thumb rule method :
I know from my past experience that a normal residential building needs around 3 to 4 Kg of steel per sqft .of built up. This data has been worked out from the previous projects . I also recommend to each student to keep this statistics updated for their projects.
Suppose you ask me how much steel shall be required for a residential project where built up area is say 22,000 Sqft.
My immediate answer would be 22,000 x 4 = 88,000 Kg or 44 MT.
Such method is useful for arriving at the purchase quantity or for taking quotations from the steel traders. There could be variations depending upon the design philosophy.
Method 02 :
From Bill of quantities .
Quantities of various RCC elements are known from the bill of quantities.
Now suppose we know that footings need 50 Kg/CuM of reinf. steel so an if the quantity of footings is 100 CuM , we come to know that reinf in footings shall be 50*100 = 5000 Kg or 5 MT.
Method 03 :
This is the most accurate method .
We take the RCC drawing and for each element , calculate the cutting length and nos for each of the bars.
Schedule of bar weight is also available.
Thus , we can find out :
W = N*CL*U
W : reinforcement weight.
N : Numbers
CL : cutting length
U : Unit weight of the bar
It is advisable to prepare a bar bending schedule which is very scientific method and is also useful for cross checking at site.
The bar bending schedule can be prepared manually or it can be prepared using the MS Excel sheets. If MS Excel sheets are used, it may take a slightly longer time initially but then in case of repetitive works , the task becomes easier to do.
In case you would like to see an example of Steel Bars calculations using the M.S. Excel Sheet , do contact me with this form :
Hope there is enough clarity now !
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