Elastic flexural-torsional buckling behavior of pre-twisted bar under axial pressure

According to deformation features of pre-twisted bar, its elastic bending and torsion buckling equation is deduced. The equation indicates that the bending buckling deformations in two main bending directions are coupled with each other, and bending and twist buckling deformations are also coupled with each other because the cross-section shear center does not coincide with the shape center. However, for pre-twisted bar with dual-axis symmetry cross-section, bending buckling deformations are independent of the twist buckling deformation. At the same time, finite element analysis of pre-twisted bar with different pre-twisted angle is put up, which points out that the assumption in literature [7] about a plane elastic bending buckling deformation curve is not correct, and the curve deviates more from a plane one as the pre-twisting angle increases. Finally, the finite element parameters analysis is carried out on the relationships between elastic bending buckling critical capacity with pre-twisted angle and with bending rigidity ratio. The existence of the pre-twisted angle leads to "resistance" effect of the stronger axis on buckling deformation in the direction of other axis enhances the elastic bending buckling critical capacity. The "resistance" is getting stronger and the elastic buckling capacity higher as the cross section bending rigidity ratio increases.