Civil Engineering MCQJE Level Civil Engineering
The moment of inertia (I) of a hollow circular section with outer diameter D and inner diameter d is:
Strength of MaterialsStrength of MaterialsMEDIUM
Choose the correct answer
A
π(D⁴ + d⁴)/64
B
π(D⁴ − d⁴)/64
C
π(D² − d²)/4
D
π(D³ − d³)/64
Correct Answer
B. π(D⁴ − d⁴)/64
Why is this the answer?
I = π/64 × (D⁴ − d⁴). For hollow tube: material removed from centre reduces I. The outer fibres contribute most to I (I ∝ y⁴). Used for: column design, pipe cross-sections, circular hollow sections (CHS). Polar moment J = π/32 × (D⁴ − d⁴) = 2I for torsion.
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