Question: In the absence of detailed design, the percentage of steel for reinforced concrete may be taken as approximately:
A) 0.8%
B) 1.0%
C) 1.15%
D) 1.5%
Explanation:
According to IS 456:2000, Plain and Reinforced Concrete – Code of Practice (Clause 26.5.2.1), in the absence of detailed calculations, the percentage of steel required for different grades of concrete may be taken as approximately:
- For M 20 grade concrete: 0.8%
- For M 25 grade concrete: 1.0%
- For M 30 grade concrete: 1.15%
- For M 35 grade concrete and above: 1.5%
Therefore, option C is the correct answer.
The percentage of steel is calculated as (area of steel reinforcement / area of concrete) x 100. The steel percentage depends on the grade of concrete and stress in steel and concrete based on the design. In the absence of detailed design, IS 456 recommends approximate percentages as starting values for design calculations. Using the appropriate percentage based on the grade of concrete helps ensure adequate strength and serviceability.