All about civil construction knowledge- PARAM VISIONS

What should be the minimum distance between reinforcement bars?/ Minimum spacing between individual reinforcements.

 According to the IS-456:2000, the minimum spacing between the individual reinforcement bars is determined as follows.




A. Minimum horizontal spacing:




As per IS-456:2000, the minimum horizontal distance between the individual bars shall be the maximum of the following three conditions.


1. Equal diameter bars:



As shown in the above drawing, if all the bars spaced horizontally are of equal diameter, i.e. 20mm., the spacing as per condition-1 is 20mm.


2. Unequal diameter bars:



As shown in the above drawing, if all the bars spaced horizontally are of unequal diameter, i.e. 25mm. & 16mm, the spacing as per condition-2 is 25mm.

3. Aggregate size:

 Suppose if we use a coarse aggregate of 20mm. size, the minimum spacing as per condition - 3 is

= [nominal size of coarse aggregate + 5mm.]

= [20mm. + 5mm.] = 25mm.

Here, the maximum value in all three conditions is 25mm.

 So, we have to consider 25mm. as the minimum horizontal spacing.


If we use a coarse aggregate of  25mm. size., the minimum spacing will be

= [25mm.+ 5mm.] = 30mm.


 Here, we have to consider 30mm. (greater value)  as the minimum horizontal spacing.



B. Minimum vertical spacing:



As per IS-456:2000, the minimum vertical distance between the individual bars shall be the maximum of the following three conditions.


1. Minimum requirement:



 In any situation ( condition-1), the minimum vertical bar spacing shall not be less than 15mm.

If the diameter of the bars is  ≤12mm., the minimum vertical distance shall be 15mm. In this case, we cannot consider 12mm. ( bar dia.) as the minimum spacing.


2. Aggregate size:

 Suppose we use a coarse aggregate of 20mm. size, the minimum vertical spacing as per condition - 2 is

= [ 2/3 × nominal size of coarse aggregate ]

= [2/3 × 20mm.] = 13.33mm.



3. Bar diameter:





As you can observe in the above drawing, if the diameter of the vertical layer of bars is 20mm., the minimum vertical spacing shall be equal to the bar diameter, i.e. 20mm.

Out of all these three conditions, the maximum value is 20mm.

 Here, we have to consider 20mm. as the minimum vertical spacing.


Note:

1. Whatever might be the permutation & combination of conditions, in all cases you have to choose the greater value as a minimum spacing.

2. Minimum spacing is the clear span ( not c/c distance) between the individual bars. 


Thank you for going through this article. Have a good day 😄.

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