What is Unit Weight of Steel Bars ? : With Numerical Examples ( Specific Weight)

Steel is a variety of iron, containing 0.1 to 1.5% carbon in the form of cementite. It is a widely used civil engineering construction material with high tensile strength. After knowing the unit weight of steel, we can determine the total weight of steel bars required for the project construction.

  1. Unit Weight of Steel Bars – In kg/m³  

It is the ratio of the weight of steel per unit volume.

Its SI unit is kg/m³.

Unit weight of steel is 7850 kg/m³.

  2. Unit Weight of Steel Bars – In Kg/m  

It is the ratio of the weight of steel per unit length.

It is expressed in kg/m.

  a. Determination of unit weight of flat steel bars  

For determining the unit weight of flat steel bars; the thickness and width of the flat bar should be known.

Take steel density as 7850 kg/m³ and the length of the bar as unity.

The formula for calculating the weight of the flat bar,

Weight = Volume × Density

Weight of flat steel bar= (Length × Width × Thickness) × Density of steel

Unit weight of flat steel bar = ( 1 × Width × Thickness) × Density of steel

Numerical

Determine the unit weight of flat steel of thickness 10 mm and width 20 mm.

Solution,

Weight of flat steel = Volume of steel × Density of steel

Weight of flat steel = (Length × Width × Thickness) × Density of steel

Unit weight of flat steel = ( 1 × 0.02 × 0.01) × 7850

= 1.57 kg/m

  b. Determination of unit weight of circular steel bars  

This function is only applicable for circular steel bars whose density is 7850 kg/m³.

Consider,

The length of the rod is unity ( 1m ).

The density of steel is 7850 kg/m³.

Take d as the diameter of the rod (in mm).

The weight of the steel rod is calculated as:

Weight of steel rod = Volume of steel rod × Density of steel

Weight of steel rod = (Cross-sectional Area of rod × Length) × Density of steel

Unit weight of steel rod = ( πd²/4 × 1) × 7850

= ( πd²/4 × 1000) × 7850/1000000

= d²/162 kg/m

{ 1m length= 1000 mm length

7850 kg/m³ = 7850/ (100 *100*100) = 7850/1000000 kg/mm³}

Unit weight of steel rod = d²/162 kg/m

where,

d= diameter of steel rod in mm

Again,

Unit weight of steel rod = d²/533  kg/foot

where,

d= diameter of rod in mm

Numerical

Determine the unit weight of steel rods of diameters 10 mm and 20 mm.

Solution,

Unit weight of steel rod for 10 mm diameter = d²/162 = 10² / 162

= 0.617 kg/m

Unit weight of steel rod for 20 mm diameter = 20² / 162

= 2.469 kg/m

Unit Weight of Circular Bars – In meter

Unit Weight of Circular Bars – In Feet