Ag : Gross cross-sectional area of member

Cw : Warping constant, in.6 (mm6)

E: Structural steel modulus of elasticity

Fcr : Critical stress

Fe : Elastic buckling stress determined according to Equation E3-4

Fey : Elastic buckling stress in buckling limit state with bending around y-axis

Fez : Elastic buckling stress in torsional buckling limit state z-axis

Fy : Specified minimum yield stress of the type of steel being used

G: Shear modulus of elasticity of steel = 11,200 ksi (77 200 MPa)

H: Flexural constant

K : Effective length factor

L: Laterally unbraced length of the member

r: Radius of inertia

Flexural - Torsional Buckling Limit State

  • The buckling deformations consist of a combination of twisting and bending about two flexural axes of the member.

  • The symmetry axis is the y-axis, where the buckling around the y-axis is caused by the tilting and rotation of the element around its longitudinal axis. The limit state of flexural-torsional buckling is applicable to columns with singly symmetric shapes, such as double angle, T- and U-shapes and asymmetric cross-sections.

Design with AISC 360-16

  • The compressive strength of the elements is determined according to the axial force acting from the section center of gravity.

  • With the symmetry axis being the y-axis, the elastic buckling stress Fe in the flexural-torsional buckling limit state where buckling around the y-axis occurs by tilting and rotating around the longitudinal axis, Fe equation E4-3 is calculated.