Details of reinforcements in column
Reinforcement in column is arranged to minimize the column size. The primary reinforcement remains longitudinal, parallel to the direction of the load and comprises of bars which are set in a square, rectangular or circular shape.
Main steel is arranged to withstand compression load together with concrete.
Reinforcement requirements (Longitudinal steel Ast)
- Lowest Ast 0.8% of C/S
- Highest Ast 6% of C/S
The purpose of specifying a highest percentage of steel is to arrange reinforcement maintaining specific limit to get rid of congestion of reinforcement so that the process does not become complicated to set the concrete and strengthen it.
Lowest 4 bars in rectangular/square column and lowest 6 bars in circular shape column.
The bar should not be under 12 mm.
The nominal cover shall any case should not be under 40 mm.
Lowest distance between individual bars should be as follow :-
- the diameter of greater bar
- 5 mm more nominal maximum size of coarse aggregate
Spacing of longitudinal bars should not be in excess of 300 mm from the edge of the column.
For rectangular column, the reinforcement should be allocated evenly on four sides.
The numbers of bars in column differs from 10, 12, 14, 16 of changeable diameter.
They produce main bars with various diameter ranging from 16mm, 20mm, 25 mm.
For circular column, there should be 6 nos. 20 mm dia. bar and 6 nos. 16mm dia bar.
The effective length should be 48 times the diameter of bar.
