How to calculate the size of the columns? / How to find the dimensions of the columns

 Let us find out the size of the column for a total load acting over it. Let us consider the total axial load over the column as 1650KN.

Given data:

Total load over the column = 1650KN. = 1650 x 10³N

To find:

Column size =  L x B =?

Calculation:

Factored load = Pu = [1.5 x 1650KN]

                          Pu = 2475KN. =2475 x 10³N

Let us use M30 grade concrete & Fe415 steel in this column.

As per IS code

Pu = [0.4 x fck x Ac + 0.67 x fy x Asc]

Where,

Pu = Ultimate load considered = 2475 x 10³N

fck = Characteristic compressive strength of concrete = 30 N/mm²

fy = Yield strength of steel = 415 N/mm²

Ac = Sectional area of concrete =?

Asc = Sectional area of steel

Let us provide 1.5% of steel (Asc ) in the column

which means Asc = 1.5% of Ac. = 0.015Ac

   Pu = [0.4 x fck x Ac + 0.67 x fy x Asc]

  2475 x 10³N = [(0.4 x 30 x Ac )+ (0.67 x 415 x 0.015Ac) ]

  2475 x 10³N = [12 Ac + 4.171Ac ]

   2475 x 10³N = [16.171 Ac ]

Ac =  2475 x 10³N ➗ 16.171 N/mm²

      = 153.05  x 10³ mm²

      = 1,53,051mm²

1. Square column:

If we go for a square column

Length( L) = breadth ( B )

The sectional area of the column

Ac = [ L x B ]= L²

L² = 153051mm²

L = √ 153051

   = 391.21mm.

The size of the column will be 391.21mm. x 391.21mm.

By rounding off, let us provide a column of size 400mm. x 400mm.

2. Rectangular column:

Practically,  in residential buildings, we take the breadth of the columns as 225mm. ( 9" ) to match the width of the wall.

Therefore,

[L x B] = 153051mm²

[L x 225mm.] = 153051mm²

L = [153051mm² ➗ 225mm.]

   = 680.2mm.

The size of the rectangular column = 225mm. x 680mm.

OR

 If we provide a column having a width of 300mm.(12")

L = [153051mm² ➗ 300mm.] 

    = 510mm.

The column size = 300mm. x 510mm.

I hope you understood the concept.

Note: 

1. This calculation method can be used for general residential buildings. 

2. Multi-storeyed building involves several design criteria to calculate the dimensions.

Go through the article 👇

👀.  How to design the diameter & no. of reinforcement bars required in a column?

To go through all types of structural design articles, click here.

Thank you for going through these calculation steps❤. Have a good day 😄.

   

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