As per IS-456, the cross-sectional area of longitudinal reinforcement in columns shall not be less than 0.8% and should not exceed 6%.
Now, let us find out the percentage of longitudinal steel in the c/s area of a column as shown below.
Given data:
The breadth of column = b = 450mm.
Depth of column = d = 300mm.
Longitudinal corner bars d1= 20T- 4nos.
Longitudinal mid bars d2= 16T- 4nos.
Reinforcement ratio of the column
= Sectional area of steel ÷ Sectional area of column concrete.
= Ast ÷ b × d.
First, we will calculate the sectional area of all the longitudinal bars
Ast = [{4nos × c/s area of 20mm bars } + { 4nos. × c/s area of 16mm. bars }]
=[{4nos. × (π × d12) ÷ 4} + {4nos. × (π × d22 ) ÷ 4}]
Here, d1 & d2 are the diameters of a particular bar.
Ast = [{4nos. × (3.142 × 202) ÷ 4} + {4nos. × (3.142 × 162 ) ÷ 4}]
= [{4nos. × (1256.8) ÷ 4} + {4nos. × (804.35 ) ÷ 4}]
=[{1256.8} + { 804.35 }]
= 2061.15 mm2
Reinforcement ratio
= [Ast ÷( b × d)].
= [2061.15 mm2 ÷ (450mm × 300mm)].
= [2061.15 mm2 ÷135000 mm2]
= 0.01526
Go through the article👇
👀. Checklist for column reinforcement./ Points to be checked in column reinforcement.
Reinforcement ratio of the column
The percentage of steel in the c/s area of the column
= reinforcement ratio × 100
= 0.01526 × 100
=1.526%
The calculated percentage of steel is between 0.8% & 6%. Hence safe.
Note: The sectional area of lateral ties ( stirrups) is not considered while calculating the percentage of steel in a column section.
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