It is very critical to design any structure like beam, column and slab of the building or any structure. While designing the column, we have to see whether steel is more or less than required in any member of the structure.
Columns play a very important role in the structure to transfer load of the superstructure to the soil. So, the column should be designed such that it can take the entire load safely as well as economically.
More steel rod in column may make the column brittle while less steel in column make column weak to bear tension force. Hence, let’s discuss the minimum percentage of steel in the column required for a safe column.
The minimum diameter of longitudinal reinforcement in a column is 12 mm. If the column is rectangular, then there should not be less than four steel rods in number. But, if the column is circular, then there should not be less than six rods in number.
Minimum cross-sectional area of longitudinal reinforcement in column should not be less than 0.8%. While the maximum percentage of steel rod used in the column should not be more than 6% if the column contains lapped steel rod. But if there is no lapped rod, then we can use a maximum 4% of steel rod.
The lapping of longitudinal bars should be in alternate way with minimum 48D overlapping.
Proper development length should be provided in main bars and side bars of the column. The development length may vary from 2 feet to 3 feet.
The stirrups in the steel should not be less than 7 mm. The minimum pitch of transverse reinforcement in a column is i.e spacing between the stirrups should not be more than 250 mm. Proper hook length should be provided in stirrups. Hook length may vary from 2.5 inch to 3 inch. Hook should be bent at an angle of 135°.
The maximum spacing between the two columns may be 16 feet. And the minimum size of the column should not be less than 9 inch by 9 inch i.e (9”x9”).
Minimum cover to reinforcement in column should be 40 mm. Clear cover in concrete is provided to protect the steel rod from rusting and provide the steel bars from buckling while loading on it.
I hope this article on “Minimum reinforcement in column” remains helpful for you.