Lateral Torsional Buckling

The Lateral Torsional Buckling Check is executed according to EN 1993-1-1 art. 6.3.2.1.

CHS sections (Formcode 3) are taken as non-susceptible to Lateral Torsional Buckling.

RHS sections (Formcode 2) sections are classified as non-susceptible to Lateral Torsional Buckling if the following condition is fulfilled (Ref.[9] pp.119).

With:

h	Height of RHS section
b	Width of RHS section
	Relative slenderness for weak axis flexural buckling

For all other sections the Lateral Torsional Buckling check is executed in which the elastic critical moment for Lateral-Torsional Buckling Mcr is determined by the following formula Ref.[9]:

With:

	E	Modulus of elasticity
	G	Shear modulus
	L	Length of the beam between points which have lateral restraint (= lLTB)
	Iw	Warping constant
	It	Torsional constant
	Iz	Moment of inertia about the weak axis
	kLT	LTB-length factor
	k	Factor related to end fixity
	kw	Factor to account for warping end conditions
	zg	Distance between point of load application and shear center
	zj	Asymmetry factor
	C1	Factor for taking into account the shape of the moment diagram
	C2	Factor for taking into account the position of the loading
	C3	Factor for taking into account the asymmetry of the cross-section

Haunched sections (I+Ivar, Iw+Plvar, Iw+Iwvar, Iw+Ivar, I+Iwvar) and composed rail sections (Iw+rail, Iwn+rail, I+rail, I+2PL+rail, I+PL+rail, I+2L+rail, I+Ud+rail) are considered as equivalent asymmetric I sections.

For advanced Lateral Torsional buckling analysis, see "Annex D: Use of sheeting  ".