Introduction of How to Calculate Steel in Rcc Slab
The slab is one of the most important structural elements in the construction of buildings.
Many of us are confused that how to calculate steel in RCC slab. In this article, we will get to know about the step-by-step procedure to calculate steel in RCC slab.
Slab is a structural member which enables to move from one place is floor to another floor in the structure.
The slabs are basically categorized into two types, one way slab and two-way slab. In one way slab the main bars are provided in the shorter direction and the distribution bars are provided in the longer direction.
In case of the two-way slab the main bars are provided in both directions and two-way slab is generally adopted for the construction when the length and the breadth of the slab are more than 4 meters.
Distribution bar are straight bars and the Main bars are the crank the bars at an angle of 45 degrees with a length of 0.42D
The extra bars are also provided at the bottom of the current bus which is used to maintain the framework of the slab and the length of the extra bar is L/4.
Example of Calculate Steel in Rcc Slab
Let us understand it by taking one example of a one-way slab having 5m length and 2m width. Take main bars of 12mm diameter with a spacing of 100 mm c/c.
The length of the distribution bars will be 8 mm in diameter and the spacing between the two bars is 125 mm c/c. The overall thickness of the slab is 150 mm with a clear cover of 25 mm on both sides top and bottom.
Also, Read: How to Calculate Slab Steel Quantity from Drawing | BBS of Slab
Data of Calculate Steel in Rcc Slab-
Length of the Slab = 5 m = 5000 mm
Width of the Slab = 2 m = 2000 mm
Thickenss of Slab = 0.150m = 150 mm
Step 1. Number of Main Bars & Distribution Bars:
First upon we have to calculate the number of bars required for the slabs. Here we have to calculate the number of main bars and distribution bars.
Number of Main Bars
Formula for calculating a number of bars is as follows.
Number of Bars = ( Total length of the slab – 2 x clear cover)/ centre to centre spacing of the bars + 1
Number of Bars = (5000- 2 x 25 ) 100 +1
Number of Bars = 50.5 = 51 nos
There are 51 nos of main bars are required for the slab.
Distribution of Main Bars
Calculation of number of distribution bars
Distribution Bars= (Total length of the slab – 2 x clear cover)/center to center spacing of the bars + 1
Distribution Bars = (2000- 2 x 25) /125 +1
Distribution Bars = 16.6 = 17 bars
The number of distribution bars are 17 no.
Step 2. Calculate the Cutting Length of Bars:
Calculate the cutting length of bars
For the main bars
L= Clear span of the slab
Ld = Development length which is 40 d where d is the diameter of the bar
Calculate the value of D
Development Length = Thickness of slab – 2 x clear cover – diameters bar
Development Length = 150 – 2 x 25 -12
Development Length = 88 mm
Main Bar Cutting Length
Formula for calculating the cutting length of Main Bars are as follows
Main Bar Cutting Length = Length – 2 x Ld + ( 1 x 0.42 D ) – (2 x 1 d)
Main Bar Cutting Length = 2000 + ( 2 x 40 x 12) + (1 X 0.42 X 88)- ( 2 x 1 x 12)
Cutting Length = 2972.96 mm
Cutting Length = 2973 mm
Cutting Length = 2.973 m
Distribution Bar Cutting Length
Calculating the cutting length of distribution bars
Distribution Bar Cutting Length = clear span + 2 x Ld
Distribution Bar Cutting Length = 5000 + (2 x 40 x 8 )
Distribution Bar Cutting Length = 5640 mm
Distribution Bar Cutting Length = 5.64 m
Step 3. Total Weight of Slab Steel :
Main Bars Steel Quantity Calculation
The number of main bars required are 51 nos ( as per step 1)
The length of one main bar = 2.973 m ( as per step 2)
Weight of Steel = Total Length of Steel x Length of 1 m Steel as per dia of steel (D2/ 162)
Total Length of the Main Bars = ( 51 X 2.973)
Total Length of the Main Bars = 151.623m
Weight of the Main Bars = Total Length x ( D2/ 162)
Weight of the Main Bars = 151.623 x (122/162)
Weight of the Main Bars = 134.776 kg
Distribution Bars Steel Quantity Calculation
The number of distribution bars required are 17 nos ( as per step 1)
The length of one distribution bar = 5.64 m ( as per step 2)
Total Length of the Distribution Bars = ( 17 X 5.64 )
Total Length of the Distribution Bars = 95.88 m
Weight of the Distribution Bars = Total Length x ( D2/ 162)
Weight of the Distribution Bars = 95.88 x (102/162) = 37.87 kg
Total Weight of Steel
Total Quantity of Steel Required For Slab = Weight of the Main Bars +Weight of the Distribution Bars
Total Quantity of Steel Required For Slab = 134.776 kg + 37.87 kg
Total Quantity of Steel Required For Slab = 172.646 kg
Also, Read: Calculator for Cutting Length of Stirrups | Cutting Length of Rectangular Stirrups | Cutting Length of Square Stirrups | Cutting Length of Circular Stirrups | Cutting Length of Helical Stirrups | Cutting Length of Diamond Stirrups
BBS for Slab-
Bar bending schedule or bbs plays a significant role in estimating the quantity of steel for beams, columns, and slab. It helps to find out bar shape, size, length, weight, bending dimension, etc. In two way slab, the slab is supported by four sides and loads are carried along with both directions.
How to Calculate Steel Quantity for Slab:
- Step 1. Number of Main Bars & Distribution Bars.
- Step 2. Calculate the Cutting Length of Bars.
- Step 3. Total Weight of Slab Steel.
This can be done by multiplying cross-section area of steel by its total length by density of steel which 7850 kg/m3. Total steel quantity of column equal to the sum of both main and stirrup steels.
Steel Required Per Square Feet-
If we take last thumb rule point, thumb rule for steel in RCC structure is 3.5 Kg to 4 kg/ sq.ft. of built-up area. 3500 Kg to 4000 Kg of Steel quantity is required for construction of 1000 square feet house.
Reinforcement in Slab-
Structural reinforcement is typically placed in the bottom portion of the slab thickness to increase the slab’s load capacity. Most structural slabs-on-ground have both top and bottom layers of reinforcement for controlling crack-widths and increasing load capacities.
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