Question

Limit state of lateral torsion buckling is not applicable to

(a) square shapes

(b) doubly symmetric I shaped beams

(c) I section loaded in plane of their webs

(d) I section singly symmetric with compression flanges

I had been asked this question in an online interview.

My doubt stems from Lateral Torsional Buckling topic in portion Design of Beams of Design of Steel Structures

Answer 1

Right option is (a) square shapes

Easiest explanation: Lateral torsional buckling is applicable to doubly symmetric I shaped beams, I section loaded in plane of their webs, I section singly symmetric with compression flanges. It is not possible for lateral torsional buckling to occur if moment of inertia of section  about bending axis is equal to or less than moment of inertia out of plane. So, limit state of lateral torsion buckling is not applicable for shapes bent about their minor axis for shapes with Iz ≤ Iy or for circular or square shapes.