Question

For different loading conditions, the equation of elastic critical moment is given by

(a) Mcr = c1  (EIyGIt) γ

(b) Mcr = c1 [(EIyGIt)^2] γ

(c) Mcr = c1 [√(EIyGIt)] γ

(d) Mcr = c1 (EIy /GIt) γ

I have been asked this question by my school teacher while I was bunking the class.

The query is from Lateral Torsional Buckling in section Design of Beams of Design of Steel Structures

Answer 1

Correct answer is (c) Mcr = c1 [√(EIyGIt)] γ

The best I can explain: For different loading conditions, the equation of elastic critical moment is given by Mcr = c1 [√(EIyGIt)] γ, where c1 = equivalent uniform moment factor or moment coefficient, EIy = flexural rigidity(minor axis), GIt = torsional rigidity, γ = (π/L){√[1 + (πE/L)^2IwIy]}, It  = St.Venant torsion constant, Iw = St.Venant warping constant, L = unbraced length of beam subjected to constant moment in plane of web.