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A lot of construction and manufacturing projects use steel bars. The project engineers calculate how many steel bars are required to source the raw materials. Therefore, they must determine the precise number of steel bars required. To get the accurate number, engineers do a few measurements including the calculation of unit weight of steel.
Defining unit weight of steel bars
The unit weight of an object is the weight per unit length of the object. Therefore, the unit weight of a steel bar is the weight per unit length of the steel bar.
In other words, it is the ratio of unit weight of the steel bar to its unit volume. The unit of this ratio kg/m.
Why calculate unit weight of steel bars?
Every project will find the load bearing capacity of the structures they have built using the steel bars. Weight of steel is an important component in those calculations. It also helps businesses prevent wastage of raw material.
How to calculate the unit weight of steel bars?
Steel bars can be of circular or rectangular cross section. We will examine how to calculate the unit weight of steel round bars with a circular cross section as these are the most widely used.
Today steel bars come in a variety of sizes including 8 mm, 10 mm, 12 mm, 16 mm, 20 mm, 25 mm, 32 mm and 36 mm. Here size means the diameter of the bar which is the end-to-end measurement of the circular face the at the bar.
The formula for calculating unit weight of steel bars is Weight (W) = Volume (V) x Density (D). Therefore, first we must calculate the volume of the bar. Density of the steel typically ranges from 7750 to 8000 kg/m3.
Let us look at how to calculate the unit weight of steel bars with an example:
Here are the measurements of a steel bar:
Height of the rod = 1 m
Diameter of the rod = 20 mm
Therefore, radius = 10 mm
Density = 7800 kg/m3
To apply the formula of unit weight of steel we must first find out the volume of the steel bar:
Volume (V) = Area (A) x Height (h)
Unit area of the steel bar (A) = πr²
= 3.14 x 102
A = 314 mm2
Converting mm2 into m2
A = 314 mm2 = 0.000314 m2
V = A x H
= 0.000314 m2 x 1 m
= 0.000314 m3
Weight = V x D
= 0.000314 m3 x 7800 kg/m3
= 2.44 kg
So, if you want to calculate the unit weight of 8mm steel bar or the unit weight of 12mm steel bar you can use the above formula.
Also read: How to calculate the weight of rectangular hollow section of steel?
Grades and sizes of steel bars as per Indian Standard codes
Given below are the nominal size groups of steel bars and steel wires and their grades according to Indian Standard code:
| Group | Size |
| Group I | 4 mm, 5 mm, 6 mm |
| Group II | 8 mm, 10 mm, 12 mm, 16 mm, 20 mm, 25 mm, 28 mm, 32 mm |
| Group III | 36 mm, 40 mm, 45 mm and 50 mm |
| Group | Strength grade |
| Group 1 | Fe 415, Fe 415D, Fe 415S |
| Group 2 | Fe 500, Fe 500D, Fe 500S |
| Group 3 | Fe 550, Fe 550D |
| Group 4 | Fe 600 |
| Group 5 | Fe 650 |
| Group 6 | Fe 700 |
Source: https://bis.gov.in/wp-content/uploads/2020/07/PM-IS-1786-JULY-2020-Revised-4.pdf
The weight of steel is generally measured in kilograms or tonnes. Construction projects required tonnes of steel sourced as raw materials. Measuring the unit weight of steel bars is necessary to determine the load bearing capacity of pillars, columns, etc.
Also read: What are TMT bars? Key features and advantages
