Effects of warping torsion on the buckling behaviour of slender box sections

Abstract

AbstractWelded steel box sections are applied in various fields like in bridges as well as in structural engineering and industrial constructions. Apart from square‐shaped sections, these sections have the tendency to warp under torsion. Therefore – in case of torsional loading – restraints of the member's longitudinal displacements always result in additional stress components, the so‐called warping normal stresses and warping shear stresses. Due to the complex distributions of this warping stress components, frequently simplifications are done in practice within the design for ULS. It means, that only the St Venant shear stresses are considered, without taking into account the warping stresses. The neglect of these locally restricted warping stress fields seems accurate according to the ductile material behaviour of steel, as long as no part of the member is susceptible for local buckling. Within this paper a comprehensive study for slender box sections is presented, whether a buckling analysis with only the St Venant shear stresses, provides sufficient safety against buckling. The investigation included members under pure torsion as well as combined loading – consisting of axial force and torsion or bending and torsion. The ultimate load carrying capacity of the box section member was compared with the isolated buckling capacity of the individual plates with all‐round hinged supports, under only St. Venant shear stresses, while neglecting all additional occurring warping effects.