ELASTIC FLEXURAL-TORSIONAL BUCKLING BEHAVIOR OF PRE-TWISTED BAR UNDER AXIAL PRESSURE

According to deformation features of pre-twisted bar, the governing equation for elastic flexural-torsional buckling is deduced, which indicates that the bending buckling deformations in two main bending directions are coupled, as well as bending and twist buckling deformations due to the noncoincidence of shear center and shape center of the cross-section. On the other hand, if the cross section is dual-axis symmetric, 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 performed, which demonstrates that the assumption in Frisch-Fay R about a plane elastic bending buckling deformation curve is not correct, the larger the pre-twisting angle, the more significant deviation of the curve from a plane. 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 weaker axis, and enhances the elastic bending buckling critical capacity. The ‘resistance’ effect is getting stronger and the elastic buckling capacity is getting higher as the cross section bending rigidity ratio increases.