Question

Formula to clculate diameter of bar in beam if weight is given

Answer 1

The Formula: D²L/162

Where,

D = Diameter of steel bar in millimeter
L = Length of steel bars in meter

Understanding the Formula

We know, the weight of a material is,

= Cross sectional area of the material x Length of the material x Density of the material

For steel bar this is also same.

Weight of steel bars= Cross sectional area of steel bar x Length of steel bar x Density of steel bar.

That means,

W = A x L x ρ

Where,
A = Area = πD²/4 
π (pai) = 3.14
D = Diameter of steel bar in millimeter
L = Length of steel bar in meter
ρ (Rho) = Density of steel bar = 7850 kg/m³

Therefore,

W = 3.14 x D²/4  x L x 7850

But there are two conflicting unit in the formula. Those are millimeter for D and m for ρ (Rho).

We have to convert either D or ρ to same unit.

Let’s convert D from millimeter to meter.

1 millimeter = 1/1000 meter

Lets implement this to the formula,

W= 3.14 x D²/(4x1000x1000) x L x 7850

= D²L/162