Why d2/162.2 is used to calculate weight of Rebar?
The most common question which people ask in interview is about, why we take d^{2}/162.2 for calculating weight of rebars and how it is derived.
The formula is used to find out the weight of steel rebar. It is the Mild Steel used as structural steel which tends to show low carbon content with a carbon parentage of ( 0.2- 0.35%)
To find the derivation of d^{2}/162.2 , Firstly we should know the physical properties of the Steel.
S.No | Properties | Value |
1. | Unit mass of steel | 7850 kg/m^{3} |
2. | Modulus Of Elasticity | 2 x 10^{5} N/mm^{2} |
3. | Modulus Of Rigidity | 0.769 x 10^{5} N/mm^{2} |
4. | Coeff Of Thermal Expansion | 12 x 10^{-6} /degree C |
We know the formula of Calculating Mass, which is
Mass= Density x Volume
To find Out the formula we will need the density and the volume of steel member.
Density = 7850 kg/m^{3}^{}
Volume Of steel = Volume of Cylinder = π x R^{2 }x Height
Derivation
We calculate the formula for Bar Length = 1 meter.
Therefore,
Mass = Density x Volume
= π x R^{2 }x Height x 7850 kg/m^{3}
= 3.14 x D^{2}/4 x 1000 mm x 7850/1000x1000x1000
= (D^{2 }x 6162.25) / 100000
= d^{2} x 0.00616225
= d^{2 }x (1/0.00616225)^{-1}
= d^{2 }/ 162.278
= d^{2} / 162.28
This this how the Formula has been derived and if we want to take out the weight in ft , than the formula is used as d^{2}/533.
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