All about civil construction knowledge- PARAM VISIONS

How to replace or change dia. of bars in column?/Calculating steel replacement in columns on site.

 Let us consider an RCC column of size 380mm. x 230mm. as shown below.

Now,  we need to replace the main bar of 16mm. dia. with 12mm. bar due to its non-availability on-site.

Given data:

Main bar dia = 16mm.

No. of bars = 4nos.


The sectional area of 16mm. bar

 =[ π x d² ➗ 4]

= [3.142 x 16² ➗ 4]

= [804.352 ➗ 4]

201.088 mm².

The sectional area of the total no. of main bars

= [sectional area of 1 bar x no. of bars]

= [201.088 x 4nos.]

= 804.35mm².

Now, the sectional area of 12mm. bar

=[π x d² ➗ 4]

= [3.142 x 12² ➗ 4]

= [452.448 ➗ 4]

113.11 mm².

No. of 12mm. bars required for replacement

= [Total sectional area of existing bar ➗Sectional area of a single replacing bar]

= [804.35mm².➗ 113.11 mm²]

= 7.11 nos.

By rounding off = 8 nos.


1. Always we have to round off the total no. of bars to the upper value.

2. To maintain symmetry, we cannot provide an odd no. of bars in columns.

Therefore, we have to provide 8nos. of 12mm. bars.


1. The replacement of bars is uneconomical, as we need to maintain symmetry in columns.

2. Again, we need to provide extra stirrup for a higher no. of replaced bars.

3. The replacement is only thought-out when there is a time constraint to complete the project.

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


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