How to make the design of RCC column

A column is considered to be a vital component of the structure. A structure mainly stands on a column. The main purpose of the column is to withstand axial and lateral forces with or without moment and transmit them securely to the footings in the ground.

The floors in a structure are supported by the columns. Slabs and beams pass the stresses on the columns. Therefore, it is imperative to design strong columns.

A column is also known as a compression member, the effective length of it surpasses three times the minimum lateral dimension. Compression member whose length does not surpass three times the minimum lateral dimension, is formed with plain concrete.

The axial load bearing strength of a column is worked out from the following formula :-

P_u = 0.4 f_ck Ac + 0.67 f_y A_sc according to IS 456-2000

Least eccentricity of column
Emin > l/500 + D/30 >20
Here, l denotes unsupported length of column in ‘mm’
D denotes lateral dimensions of column

Types of Reinforcements for columns:

Longitudinal Reinforcement

1. Least area of cross-section of longitudinal bars should be no less than 0.8% of gross section area of the column.
2. Maximum area of cross-section of longitudinal bars should not surpass 6% of the gross cross-section area of the column.

Also Read: How to measure quantity of steel for the square RCC Column

3. The bars should not be lower than 12mm in diameter.
4. Minimum number of longitudinal bars should remain four in rectangular column and 6 in circular column.
5. Span of longitudinal bars calculated along the boundary of a column should not surpass 300mm.

Transverse reinforcement

1. It may come in the type of lateral ties or spirals.
2. The diameter of the lateral ties should not remain lower than 1/4th of the diameter of the biggest longitudinal bar and in no case lower than 6mm.

The pitch of lateral ties should not go beyond

1. Minimum lateral dimension
2. 16 x diameter of longitudinal bars (small)
3. 300mm

Helical Reinforcement

The diameter of helical bars should not be lower than 1/4th the diameter of biggest longitudinal and not lower than 6mm. The pitch should not surpass (when helical reinforcement can be arranged);

1. 75mm
2. 1/6th of the core diameter of the column

Pitch should not be lower than,

1. 25mm
2. 3 x diameter of helical bar
3. Pitch should not go beyond (when helical reinforcement can’t be arranged)

Minimum lateral dimension

1. 16 x diameter of longitudinal bar (smaller)
2. 300mm