As per IS 456:2000, the minimum cross-sectional area of longitudinal reinforcement (irrespective of load requirement) in a RCC column of size 150 × 300 mm shall NOT be less than _____. Consider the limit state method of design.
- A240 mm²
- B360 mm²Correct
- C440 mm²
- D780 mm²
Solution
Concept
IS 456:2000 requires at least 0.8% of the gross cross-sectional area of a column as longitudinal steel.
Formula
Asc,min = 0.8% × Ag
Step-by-step solution
1. Gross area: Ag = 150 × 300 = 45000 mm². 2. Minimum steel = 0.8% of Ag. 3. Asc,min = 0.008 × 45000 = 360 mm².
Explanation
IS 456:2000 says column longitudinal steel must be at least 0.8% of the gross area. The gross area here is 45000 mm². So the minimum steel is 360 mm².
Why the other options are wrong
A: 240 mm² is less than 0.8% of the gross area. C: 440 mm² does not match any percentage limit in the code. D: 780 mm² is not the minimum; the code's maximum limit is 6%, which is 2700 mm².
Shortcut
Minimum steel = 8 × Ag / 1000, so 8 × 45 = 360 mm².
Common mistake
Using 0.12% or 0.15% (the slab minimum) or 4% (the practical maximum) instead of 0.8% for columns.
Correct answer: B) 360 mm²