How To Calculate Steel Quantity In Slab

In this civil engineering article, you will gather knowledge on how to work out the quantity of steel inside a flat, one way or two way slab.

Suppose there are two slabs, one is big (for room) and other is small (for bathroom).

The dimension of the big slab is 5m x 3m and the dimension of small slab is 2.5m x 1.5m

The calculation is done with the area method :-

Area of small slab = 2.50 x 1.50 = 3.75 m²

Area of big slab = 3.0 x 5.0 = 15 m²

So, total area = 3.75 + 15 = 18.75 m²

ALSO READ : CANTILEVER SLAB REINFORCEMENT DETAILS

Suppose, the steel bars with diameter 12 mm (main bars in horizontal direction) and 10 mm (cross bars are used in the slab in vertical direction). The main bars are used in short span and cross bars are used in long span).

Suppose, there is one slab with dimension 1 m x 1 m. Main bars of 12 mm and cross bars of 10 mm are applied in the slab.

The spacing of main bars is taken as 4 inches or 100 mm. To convert it to meter, just divide with 1000 i.e. 100/1000 = 0.10m.

The spacing of cross bar is taken as 5 inches or 125 mm or 0.125 m.

To determine the numbers of main bars, the following formula is used :-

Longer Span / Spacing + 1 = 1.0 / 0.10 + 1 = 11 numbers (as length = 1 meter)

Here, spacing means the distance among two horizontal bars.

Here, the starting bars is added as 1.

To determine the total length of main bars (horizontal bars), the following formula is used :-

Total length = Length of one bar x Numbers of bars

Total length = 1 m x 11 = 11 m (bars with diameter 12m)

To determine the numbers of cross bars (vertical bars), the following formula is used :-

Numbers of cross bars = Shorter Span / Spacing + 1

Numbers of cross bars = 1.0 / 0.125 + 1 = 9 numbers (as width = 1 meter)

Here, spacing means the distance among two vertical bars.

To determine the total length of vertical bars, the following formula is used :-

Total length = Length of one bar x Numbers of bars

Total length = 1.0 x 9 = 9 m (bars with diameter 10m)

Now, the total weight of bars will be calculated as follow :-

Weight of 12 mm bars + Weight of 10 mm bars

To determine the length for 1 meter, the formula is d²/162

To determine the total length, multiply with length i.e. (d²/162 x l)

Total weight = (d²/162 x l) + (d²/162 x l)

(d²/162 x l) = 12 x 12 / 162 x 11 = 9.77 kg (for 12 mm dia bar)

(d²/162 x l) = 10 x 10 / 162 x 9 = 5.55 kg (for 10 mm dia bars)

Previously, we find out total area = 18.75 m2

So, total weight of 12 mm dia bars will be calculated as follow :-

Ø12 mm = 18.75 x 9.77

So, total weight of 10 mm dia bars will be calculated as follow :-

Ø10 mm = 18.75 x 5.55