Question

Consider a doubly reinforced RCC beam with the option of using either Fe250 plain bars or Fe500 deformed bars in the compression zone. The modulus of elasticity of steel is \( 2 \times 10^5 \, \text{N/mm}^2 \). As per IS456:2000, in which type(s) of the bars, the stress in the compression steel \( (f_{sc}) \) can reach the design strength (0.87 \( f_y \)) at the limit state of collapse?

• A. Fe250 plain bars only
• B. Fe500 deformed bars only
• C. Both Fe250 plain bars and Fe500 deformed bars
• D. Neither Fe250 plain bars nor Fe500 deformed bars

Hint:

For RCC beams with doubly reinforced sections, plain bars (Fe250) can achieve the design stress, while deformed bars (Fe500) cannot reach the design strength in the compression zone as per IS 456:2000.

Answer 1

The Correct Option is A

In a doubly reinforced RCC beam, the stress in the compression steel is given by the design strength \( 0.87 f_y \). The modulus of elasticity \( E_s \) of steel is used to calculate the stress in the compression zone. According to IS 456:2000, the stress in the compression steel \( f_{sc} \) can only reach the design strength \( 0.87 f_y \) if plain bars (such as Fe250) are used. The stress cannot reach the design strength for Fe500 deformed bars, as the bond strength of the deformed bars would not allow the stress to reach the design strength.
Thus, the correct answer is (A): Fe250 plain bars only.
\[ \boxed{\text{The correct answer is (A). Fe250 plain bars only.}} \]