Following Are The Steps To Calculate The Quantity Of Steel For RCC Slab
1. Prepare a bar bending schedule in order to classify different shapes of bars (bent up bar, straight anchor bar, eos bar, curtail bar, etc) and diameters.
2. List down all the shapes of bars from the drawing.
3. Count the number of bars of each of those shapes.
4. Then calculate the cutting length of each of those bars.
Cutting length of bar = (length of the member – deduction for cover on both sides) + development length.
5. Then calculate the unit weight of each dia bar by the following formula:
W = D^2/162*L
Where ;
W: Unit weight of steel bar in kg
D: Diameter of steel bar in mm
L: Total length of bar in m
6. Then calculate the weight of the rebar
Weight of rebar= no of bars x cutting length x unit weight
7. Add all the weight to get the total steel quantity.
NOTE :
1. Minimum % Of Steel Are
1. For Beam (Tension reinforcement)
As = 0.85bd/fy of gross cross-section area
2- For Slab = 0.12% of total area
3- For Column = 0.8% of cs area
2. Maximum % Of Steel Are
1. For Beam = 4 % of cross-section area
2. For Slab = 4% of cross-section area
3. For column = 6% of cross-section area
3. Development Length
Is usually specified in the drawings, but if not then you can calculate it as
D.L = Depth – 2 times cover
4. Binding wire = 10 grams per kg of reinforcement
5. No. of stirrups = (length of member – 2 x cover ) / spacing + 1
Calculation of unit weight of steel bars
After estimating it is very important to know the unit weight of steel bars because we estimate them as 100 meters 20mm Ø bar, or 100 feet 16mm Ø bar, etc (ø is the symbol of diameter).
But steel bar suppliers will not understand this notation, they measure the steel bars in weight. So we have to order them in kg or quintal or ton. In this article, we will discuss how to calculate the unit weight of steel bars of different diameters.
The formula: W = D^2L/162
W = Weight of steel bars.
D = Diameter of steel bars in mm.
L = Length of bars in meters.
Example 1:
Calculate the weight of 60 meters long 12 mm Ø bar.
Here, D = 12 mm.
L= 60 m.
We know that, W = D2L/162
W = 12^2 x 60/162 = 53 kg
Weight of 60 m 12mm Ø bar is 53 kg.
Let’s look for another example.
Example 2:
Calculate the weight of 100 m 16 mm Ø bar.
Here, D = 16 mm.
L = 100 m.
W = 16^2 x 100/162 = 158 kg.
If we put 1 meter length for each diameter of steel bar in the formula then we will get the unit weight.
10mm Ø bar = 10^2 x 1/162 = 0.617 kg/m
12mm Ø bar = 12^2 x 1/162 = 0.888 kg/m
16mm Ø bar = 16^2 x 1/162 = 1.580 kg/m
20mm Ø bar = 20^2 x 1/162 = 2.469 kg/m
If we multiply the length of bars with this unit weight we will get the total weight of steel bars.
For example, the total weight of 1000 meter long 20mm Ø steel bar is 1000 x 2.469 = 2469 kg = 2.469 ton
Using the same method we can calculate the unit weight of different steel bars.
Here I have calculated in meter but we can also calculate in foot. To calculate in foot we have to use the following formula:
W= D^2L/533
Where D = Diameter of bars in mm.
L = Length of bars in foot.
