Section modulus of the rectangular section with breadth b and depth d is
- Abd³/12
- Bbd³/3
- Cbd²/6Correct
- Dbd²/3
Solution
Concept
Section modulus of a rectangle
Formula
Z = I / y = (bd³/12)/(d/2) = bd²/6
Step-by-step solution
1. I = bd³/12; extreme fibre distance = d/2. 2. Z = I/y = bd²/6.
Explanation
Section modulus is the moment of inertia divided by the distance to the extreme fibre.
Why the other options are wrong
bd³/12 is the moment of inertia, and the other options do not have the right dimensions or constants.
Shortcut
Rectangle Z = bd²/6.
Common mistake
Giving I instead of Z.
Correct answer: C) bd²/6