For an unsymmetrical angle section, the principal axes of inertia pass through which point?

Question

Question

This question was previously asked in

RRB JE CE 22 Apr 2025 Shift 1 CBT 2 Official Paper

Answer 1

Explanation:

The centroid of the section

The principal axes of inertia always pass through the centroid of the cross-section.
These axes are the directions about which the product of inertia is zero, and they represent the natural orientation of the section for bending and twisting behavior.
For unsymmetrical sections like unequal angle sections, the principal axes are inclined and not aligned with the geometric axes, but they still intersect at the centroid.

Additional InformationThe midpoint of the shorter leg –

This is just a geometric point on one part of the section and does not represent any specific relation to the principal axes.

The intersection of the legs –

While this point is important for fabrication and reference, it does not necessarily coincide with the centroid of the section, especially for unsymmetrical angles.

The midpoint of the longer leg –

Like option 1, this is a geometric reference point, but it has no direct relation to the principal axes of inertia.