According to IS 456:2000, an equivalent moment in a rectangular RCC beam under torsion can be calculated as
- AMe = Mu + Tu(1 + D/b)/1.7Correct
- BMe = Mu + Tu
- CMe = Mu + Tu(D/b)/1.7
- DMe = Mu + Tu(D/b)/7
Solution
Concept
Equivalent bending moment in torsion (IS 456 cl. 41.4.2)
Formula
Me1 = Mu + Mt, Mt = Tu (1 + D/b)/1.7
Step-by-step solution
1. Equivalent moment Me1 = Mu + Mt. 2. Mt = Tu (1 + D/b)/1.7.
Explanation
IS 456 converts the torsion into an equivalent bending moment for the design of longitudinal steel.
Why the other options are wrong
B ignores the section dimensions, C and D omit the 1 or use a wrong divisor.
Shortcut
Mt = Tu(1 + D/b)/1.7.
Common mistake
Dropping the 1 in (1 + D/b).
Correct answer: A) Me = Mu + Tu(1 + D/b)/1.7