Question

Section modulus is defined as

1. \(\frac{Moment\; of\; inertia\; about\; the\; neutral\; axis}{Square\; of\; the\; distance\; of\; neutral\; axis\; from\; farthest\; point}\)
2. \(\frac{Moment\; of\; inertia\; about\; the\; neutral\; axis\;}{Distance\; of\; the\; most\; distant\; point\; from\; the\; neutral\; axis\;}\)
3. \(\frac{Bending\; moment}{Moment\; of\; Inertia}\)
4. None of the above

Answer 1

Correct Answer - Option 2 : \(\frac{Moment\; of\; inertia\; about\; the\; neutral\; axis\;}{Distance\; of\; the\; most\; distant\; point\; from\; the\; neutral\; axis\;}\)

Explanation:

Sectional Modulus (Z):

• It is the ratio of moment of inertia (I) of the beam cross-section about the neutral axis to the distance (ymax) of extreme fiber from the neutral axis,  \(Z = \frac{I}{y_{max}}\)
• The section modulus (Z) of the cross-sectional shape is significant in designing beams. It is a direct measure of the strength of the beam. A beam that has a larger section modulus than another will be stronger and capable of supporting greater loads.

• The unit of the Section modulus is mm³.

Shapes	Section Modulus
Circular	\(~Z_{cirular\;section}=\frac{\pi{d^3}}{32}\)
Rectangle	\(~Z_{Rectangular\;section}=\frac{b{d^2}}{6}\)