Question

Describe the similarities and differences between flexural-torsional buckling and

lateral-torsional buckling. What is the coupling mechanism for each of these buckling modes?

Answer 1

Flexural torsional buckling- this type of failure is caused by a combination of flexural buckling and torsional buckling.The member bends and twists simultaneously .This type of failure can occur only with unsymmetrical cross sections ,both those with one axis of symmetry such as channels,structural tees ,double angles etc and those with no axis of symmetry such as unequal leg single angle.Generally the specification require an analysis of torsional or flexural-torsional buckling only when appropriate.

Lateral torsional buckling - Torsional buckling occurs when the torsional rigidity of the member is appreciably smaller than the bending rigidity. This type of failure is caused by twisting about the longitudinal axis of the member.It can occur only with doubly symmetrical cross section with very slender cross sectional elements.Standard hot rolled shapes are not susceptible to torsional buckling.but a member build from thin plate should be investigated for this.If sufficient end supports and intermediate lateral braces are provided ,flexural buckling will always control the torsional buckling