GATE 2026 CE (CE1) – Question 29
The required centre-to-centre spacing of 10 mm diameter bars is 150 mm to resist the design moment in a concrete slab. Instead of 10 mm diameter bars, if 12 mm diameter bars of the same grade are used, the required centre-to-centre spacing (in mm) to resist the same design moment becomes ______ (*rounded off to the nearest integer*).
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Correct answer: 216
Explanation
To resist the same moment, the area of steel per metre of slab must stay the same. The area of one bar is proportional to $d^2$, so the spacing is proportional to $d^2$. The new spacing is $150 \times \frac{12^2}{10^2} = 216$ mm.