Question

In beam design, sections are proportioned as such that _____ to achieve economy.

(a) moment of inertia about principal axis parallel to the web is equal to moment of inertia about principal axis normal to the web

(b) moment of inertia about principal axis parallel to the web is considerable larger than moment of inertia about principal axis normal to the web

(c) moment of inertia about principal axis normal to the web is considerable larger than moment of inertia about principal axis parallel to the web

(d) moment of inertia about principal axis normal to the web is considerable lesser than moment of inertia about principal axis parallel to the web

The question was posed to me in a national level competition.

Question is taken from Lateral Stability of Beams in portion Design of Beams of Design of Steel Structures

Answer 1

Correct choice is (c) moment of inertia about principal axis normal to the web is considerable larger than moment of inertia about principal axis parallel to the web

Explanation: In beam design, sections are proportioned as such that moment of inertia about principal axis normal to the web is considerable larger than moment of inertia about principal axis parallel to the web to achieve economy. Such sections are relatively weak in bending resistance.