All about civil construction knowledge- PARAM VISIONS

How to replace or change the diameter 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 number 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 number of bars to the upper value.

2. To maintain symmetry, we cannot provide an odd number 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 number of replaced bars.

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

To go through the articles on Estimation & calculation in civil engineering, click here.

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


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