Q.13 As per IS 456-2000, the flexural strength of a rectangular section of a singly reinforced RCC beam does NOT depend on which of the given options?
- AGrade of steel
- BGrade of concrete
- CDepth of beam
- DTemperatureCorrect
Solution
Concept
Moment of resistance depends on fck, fy, b, d and Ast. Temperature is not a parameter.
Formula
Mu = 0.87 fy Ast d (1 - (Ast fy)/(b d fck))
Step-by-step solution
1. As per IS 456, Mu = 0.87 fy Ast d (1 - Ast fy/(b d fck)). 2. The variables are fy (grade of steel), fck (grade of concrete), b, d (effective depth) and Ast. 3. Temperature does not appear in the formula. 4. So the answer is (D) Temperature.
Explanation
Flexural strength of an RCC beam depends on the grade of concrete, the grade of steel, the section size and the steel area. Temperature is not used in the IS 456 flexure formula. So it does not decide the flexural strength.
Why the other options are wrong
A: fy is in the Mu formula. B: fck is in the Mu formula, and xu,max/d and the limiting moment also depend on it. C: Effective depth d directly affects Mu (Mu,lim = k fck b d2).
Shortcut
Recall Mu,lim = 0.138 fck b d2 for Fe 415. Any item not in it, or in Ast, is the answer.
Common mistake
Thinking depth does not matter. In fact Mu varies with d2.
Correct answer: D) Temperature