Standard Size Of Column

Size of column depend upon several factors like load on the structure, height of the building and distance between the two column. In this post we will discuss standard size of Column for building construction.

Size of the column also depends upon the material used in column construction. Column based on material are classified as RCC column, timber column, short column, tied column and many more.

Standard Size Of Column

As stated above standard size of column depends upon many factors. But for rough idea of column size refer the table below. Detailed information about standard size of column is discussed in the later part of this post.

Standard minimum size of column and details

Details of minimum size of column that is necessary for any structure based on its height along with other details for column are given below.

Column details for 1 storey (ground floor) building

Column details for 2 storey (G+1) building

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Column details for 3 storey (G+2) building

Column details for 4 storey (G+3) building

Standard Thumb Rule Used In Construction

Nowadays minimum size of column used in construction irrespective of small building is 9″ X 12″ (225mm X300mm). Recommended grade of concrete for building construction is M20 grade, which is in the ratio of 1 : 1.5 : 3 (1 part of cement and 1.5 part of sand and 3 parts of coarse aggregate with 0.5 parts of water).

Below is the summary of the standard size of column used in 2021.

• Column Size – 9″ X 12″ (225mm X300mm)
• Main reinforcement – 6 bars of 12mm dia Fe 500 Steel
• Stirrup rings – T8mm dia bars @ 6″ (150mm) spacing
• Concrete – M20 Grade of concrete (1 : 1.5 : 3)

Quick Formula For Dimension of Column

A quick method top find the size of column based on the strength of the material and maximum load to be applied on column is given below.

N_max = A * f * Reduction Factor

Where,

• N_max = Maximum load that can be applied on column
• A = Area of Column in m²
• f = Strength of material in KN/m²
• Reduction Factor = Coefficient for taking into account risk and material variation

Factors Affecting Column Size

There are many factors that affect the size of column but most important ones are height of the building or structure, distance between columns, alignment of column and many other factors.

Factors affecting column size are given below:

• Height of the building or structure
• Distance between adjacent columns
• Load of the structure
• Architectural consideration

Let us look in detail how column size is affected by each factors and what size should be preferred for such situations.

Height of the structure

As height of the building increases the dead load and live load on the building also increases. To compensate for the increase in load we need to increase the strength of the RCC structure.

As we know that column transfer load from beams and slab to the foundation of the structure of the building. Thus size of column and reinforcement in column is needed to be increased.

Space Between Adjacent column

Distance between each column in a building should be preferably kept same between centres of 2 column. If columns are placed closer to each other then the size of column can be reduced and vice versa. This space between columns is directly proportional to the size of the column.

Distance between column is directly proportional to column size

For a 9″ X 9″ Column, the maximum distance between the column should not be more than 4 meters. If due to architectural or any other condition distance between column is more than the size of the column is increased.

Load on the structure

No standard size can be fixed for similar height building as each structure has a different function. As we know to counter the increase in height and dead load of structure, size of column is increased. Similarly for balancing live load, wind load and other loads the size of column is needed to be selected accordingly.

Thus before deciding the size of the column proper load that is going to come on the building should be worked out.

Column Size Calculation

Size of column shown above for different type of building is minimum standard column sizes for a particular types of buildings. That doesn’t mean that it is to be used everywhere.

Certain type of building condition requires stronger column section. The size of column is mainly dependent on the following factors;

• Concrete grade
• Grade of steel
• Factored load on column

Column size is decided by the following column size formula given by IS 456:2000.

Pu = 0.4 f_ck A_c + 0.67 f_y A_sc

Where,

• Pu = Ultimate Load on Column
• f_ck = Characteristics compressive strength of concrete
• A_c = Sectional Area of Concrete
• f_y = Yield strength of steel
• A_sc = Area of Steel Reinforcement
• A_c = A_g – A_sc
• A_sc = 0.01 A_g (A_g =  Gross Area of Column)
• A_c = 0.99 A_g

Example of Column Size Calculation

Let us learn how to design a column to support axial load of 600 KN by using M20 grade of concrete and Fe 500 steel grade.

From the given condition,

Pu = 600 KN,
f_ck = 20 N/mm²,
f_y = 500 N/mm²,

Assume,
Steel = 1% and
Factor of Safety = 1.5

P_u = 0.4 f_ck A_c + 0.67 f_y A_sc
900 x 10³ = 0.4 x 20 x (0.99 A_g) + 0.67 x 500 x (0.01 A_g)
A_g = 79858 mm²

For square column,

Size of Column = √79858 = 282.59 mm

Provide square column of size 285 mm x 285 mm

A_g = Provided = 81225 mm²

A_sc = 0.01 A_g = 0.01 x 81225 = 812.25 mm²

Provide 8 Nos of 12 mm Dia steel with actual area of steel = 905 mm²

The size of the column for 600 KN load is 285 mm x 285 mm (12″ x12″)

Why No Standard Size Of Column

As you have seen above that the size of column depends upon many factors, thus it would be hard to fixed the size based on these factors.

Size of column depend upon the load to be supported, type of column, distance between column, architectural design, and many other factors affect the size of column. By varying the percentage of steel the size of column can be reduced or increased.

Based on these factors we have to assume the size of column and check for safety of the structure.