What is steel?
Steel is one of the most important construction materials around the world. It is almost used in every aspect of the construction process.
Steel is an alloy of iron, carbon, and small amounts of manganese, silicon, phosphorus, and sulfur.
The carbon content in steel is limited to 2% because the amount of carbon influences the physical properties of steel such as ductility, elasticity, strength, etc.
Why steel is used as reinforcement in concrete?
The need for reinforcement in concrete comes from the fact that the concrete is strong in compression but so much weaker in tension. The tensile strength of concrete is almost one-tenth of its compressive strength.
However, the concrete experiences tension in flexural members such as beams and slabs. Even in compressive members like columns, when the load is placed eccentrically, tension is produced at one end of the column.
So we have to reinforce the concrete with another material that has great strength to withstand tensile forces and also should possess enough ductility.
Steel is selected as an ideal reinforcement for concrete because it possesses the above-mentioned properties and even has the same coefficient of thermal expansion as concrete which means both steel and concrete would expand and contract due to temperature at similar rates.
Now we know why we use steel as reinforcement in concrete. Now let’s learn how to calculate the weight of steel bars used in concrete.
Derivation of formula for calculating the unit weight of steel bar
Before getting into the derivation, let’s know that the density of steel is 7850 kg/m3.
Weight of steel bar per meter = Volume of steel bar x Density of steel bar
Volume of steel bar = Area of steel bar x Length of steel bar
Let’s consider the length of the steel bar as 1m (unit length). So,
Weight of steel bar per meter = 0.785 D2 x 1 m x 7850 kg/m3.
Since we always measure the diameter of the bar in mm, let’s convert all units to mm. (1m = 1000mm)
Weight of steel bar per meter = 0.785 D2 x 1000 mm x 7850 kg/(1000 x 1000 x 1000 mm3)
Weight of steel bar per meter = 0.785 D2 x 1000 mm x 0.00000785 kg/mm
Weight of steel bar per meter = 0.785 D2 x 0.00785 kg = 0.006162.D2 kg
Weight of steel bar per meter = D2 /(1/0.006162) kg =D2 /162.27 kg
Weight of steel bar of 1m length = D2 /162.27 Kg.
(We can round off 162.27 to 162).
If you want this formula to be in Kg per foot, then
Weight of steel bar per foot = D2/(162.27 x 3.28 ) (1m = 3.28 feet)
Weight of steel bar of 1 ft. length = D2 /532.27 kg.
(We can round off 532.27 to 532).
How to calculate the unit weight of steel bars?
Various diameters of steel bars are used in the construction field. They are of
8mm, 10mm, 12mm, 16mm, 20mm, 25mm, 32mm and 40mm diameters.
8mm diameter steel bars are used as stirrups in beams and as ties in columns. The other dia bars are used as the main reinforcing steel in the structure.
Now, let’s calculate the unit weight of steel bars,
a) 8mm rod weight
Weight of 8mm steel rod of 1m length = D2/162 = (8×8)/162 = 0.395 kg/m.
Weight of 8mm steel rod of 1ft length = D2/532 = (8×8)/532 = 0.120 kg/ft.
b) 10mm rod weight
Weight of 10mm steel rod of 1m length = D2/162 = 0.617 kg/m.
Weight of 10mm steel rod of 1ft length = D2/532 = 0.187 kg/ft.
c) 12mm rod weight
Weight of 12mm steel rod of 1m length = D2/162 = 0.888 kg/m.
Weight of 12mm steel rod of 1ft length = D2/532 = 0.270 kg/ft.
d) 16mm rod weight
Weight of 12mm steel rod of 1m length = D2/162 = 1.580 kg/m.
Weight of 12mm steel rod of 1ft length = D2/532 = 0.481 kg/ft.
e) 20mm rod weight
Weight of 12mm steel rod of 1m length = D2/162 = 2.469 kg/m.
Weight of 12mm steel rod of 1ft length = D2/532 = 0.751 kg/ft.
How to use this formula to calculate the weight of steel bars in the construction field?
Let’s assume you are going to construct a column of 3m which has four numbers of 12mm dia bars.
The quantity of steel rebar is measured in weight. So, to purchase from a shop, you need the weight of the steel bars.
Let’s calculate the total weight of steel needed,
First, you have to measure the length of one steel bar including anchorage length and clear span length. Let’s say you calculate the length of one steel bar required as 3.4m.
Total weight of steel required = ((12×12)/162) x 3.4 x 4 = 12.08 Kg.
Thus, you need 12.08 kg of steel as the main reinforcement for the above-mentioned column.
Steel rebar weight calculator
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Frequently Asked Questions (FAQ)
1) What is the density of steel?
The density of steel is 7850 kg/m3 (or) 78.5 KN/m3.
2) What is the formula to calculate the weight of steel bars?
Hope you understand everything you need to know about how to calculate the unit weight of steel. If you have any queries (or) if you find this article helpful, let us know in the comment section.