How to measure superimposed loads on a column

The objective of a column is to withstand axial and lateral forces and transmit them securely to the footings in the ground.

In this exclusive article, you will learn how to work out the superimposed loads on a column in a structure with some easy-to-follow steps.

Columns provide support to the floors in a structure. Slabs and beams transmit the stresses to the columns. So, it is crucial to make a strong column.

A column stands for a compression member, the effective length of which surpasses three times the minimum lateral dimension. Compression members whose lengths remain under three times the minimum lateral dimension, are constructed with plain concrete.

The axial load bearing strength of a column is derived from the follwoing formula :-

Reinforced Concrete Columns

Besides, axial loads, the column design is dependent on 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 categorized on the basis of various factors :-

1. Depending on shape
• Rectangle
• Square
• Circular
• Polygon

2. Depending 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. Depending on the type of loading
• Axially loaded column
• A column subjected to axial load and unaxial bending
• A column subjected to axial load and biaxial bending

4. Depending on pattern of lateral reinforcement
• Tied RCC columns
• Spiral RCC columns

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

The following types of Reinforcements for columns are found :-

Longitudinal Reinforcement
• Least area of cross-section of longitudinal bars should be minimum 0.8% of gross section area of the column.
• Maximum area of cross-section of longitudinal bars should not be in excess of 6% of the gross cross-section area of the column.
• The bars should not be below 12mm in diameter.
• Least number of longitudinal bars should be 4 in rectangular column and 6 in circular column.
• Distance of longitudinal bars measured along the perimeter of a column should not go above 300mm.

Transverse reinforcement
• It may appear in the form of lateral ties or spirals.
• The diameter of the lateral ties should not remain below 1/4th of the diameter of the greatest longitudinal bar and in no case below 6mm.

The pitch of lateral ties should not go beyond
• Minimum lateral dimension
• 16 x diameter of longitudinal bars (small) • 300mm

Helical Reinforcement
The diameter of helical bars should not remain below 1/4th the diameter of largest longitudinal and not below 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 remain under,
• 25mm
• 3 x diameter of helical bar
Pitch should not surpass (if helical reinforcement is not permitted)

Least lateral dimension
• 16 x diameter of longitudinal bar (smaller)
• 300mm

Reinforced Concrete Columns