RCC Column Design

Reinforced Concrete Columns: A column is considered as one of the most vital elements in a structure. It is similar to the legs on which a structure rests on. The purpose of a column is to withstand the axial and lateral forces and transmit them securely to the footings in the ground.

Columns mainly provide support to the floors within a structure. The Slabs and beams transmit the stresses to the columns. Therefore, proper consideration should be given to construct strong columns.

The following formula is used to determine the axial load bearing strength of a column :-

The design of the column is based on axial loads as well as several other factors. Because of beam spans, wind loads, seismic loads, point loads and various other factors, the bending moments and tortional forces are produced.

A column is segregated depending on the following factors :-

1. Based on shape: Rectangle, Square, Circular, Polygon

2. Based on slenderness ratio: The ratio of the effective length of a column to the minimum radius of gyration of its cross section is known as the slenderness ratio.

• Short RCC column, =< 10
• Long RCC column, > 10
• Short Steel column, =<50
• Intermediate Steel column >50 & <200
• Long Steel column >200

3. Based on type of loading

• Axially loaded column
• A column is susceptible to axial load and unaxial bending
• A column is susceptible to axial load and biaxial bending

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

4. Based on pattern of lateral reinforcement
• Tied RCC columns
• Spiral RCC columns
• Minimum eccentricity

Emin > l/500 + D/30 >20
Here, l denotes unsupported length of column in ‘mm’
D denotes lateral dimensions of column
Classifications of Reinforcements for columns and their requirements

Longitudinal Reinforcement:

• Least area of cross-section of longitudinal bars should have been minimum 0.8% of gross section area of the column.
• Maximum area of cross-section of longitudinal bars should not surpass 6% of the gross cross-section area of the column.
• The bars should not be lower than 12mm in diameter.
• Least number of longitudinal bars should be four in rectangular column and 6 in circular column.
• Spacing of longitudinal bars measures along the border of a column should not go beyond 300mm.

Transverse reinforcement:

• It appears as the form of lateral ties or spirals.
• The diameter of the lateral ties should not be lower than 1/4th of the diameter of the biggest longitudinal bar and in no case below 6mm.

The pitch of lateral ties should not exceed:

• Minimum lateral dimension
• 16 x diameter of longitudinal bars (small)
• 300mm

Helical Reinforcement: The diameter of helical bars should not remain lower than 1/4th the diameter of largest longitudinal and not under 6mm. The pitch should not go above (if helical reinforcement is permitted);

• 75mm
• 1/6th of the core diameter of the column

Pitch should not be less than,
• 25mm
• 3 x diameter of helical bar

Pitch should not go over (if helical reinforcement is not permissible). Least lateral dimension
• 16 x diameter of longitudinal bar (smaller)
• 300mm