What to do? If the specified bar as per design is not available on site?

We can use a simple formula for this but make sure this formula will not be applicable for high-rise buildings.

Formula –
(D1)^2/(D2)^2 = S1/S2

Where –
S1 = spacing for D1 bar
S2 = spacing for D2 bar
Example-
Suppose you have 8 mm dia bar at construction site but as per drawing we need 10 mm dia for construction. In this situation we will use that formula to get the spacing between bars.
As per drawing,
For 10 mm dia, Spacing (S1)= 200 mm
But 8 mm dia bar available at site,
So spacing (S2) = ?
Given –
D1 = 10 mm
D2 = 8 mm
S1 = 200 mm
S2 = ?

Ans –

(D1)^2/(D2)^2 = S1/S2
10^2 / 8^2 = 200/ S2
by solving this we will get the value of S2
S2 = 128 mm

So in this case we will give 128 mm spacing between bars.