05.29: Interaction curves for local and distortional buckling of polygonal tubes in combined torsion and axial loading

Abstract

ABSTRACTThis paper investigates the interaction of uniform axial loading (compressive or tensile) and uniform torsion on the linear elastic buckling behaviour of long tubes with regular convex polygonal cross‐sections. The analyses pertain to tubes of sufficient length such that the results are independent of end boundary conditions. Using the generalised constrained finite strip method (cFSM), pure local buckling is examined for triangular through octagonal tubes. The interaction curves for pure local buckling are akin to those previously generated from the exact finite strip method and a square and octagonal tube are analysed in‐depth to assess the changes in interaction behaviour as the number of sides in the section is increased. The pure distortional buckling behaviour is examined for pentagonal through octagonal tubes using recent developments in Generalised Beam Theory (GBT) and an almost linear interaction between torsion and compression is found, as has been noted previously for circular tubes. The distortional interaction curves are essentially identical for all analysed tubes.