Comparison of the Cantilever Bending Behavior of Polygonal and Rectangular Hollow Structural Sections

Abstract

Thin-walled rectangular hollow structural sections are less efficient when dealing with long un-braced deep beams that require high bending stiffness due to their susceptibility to local buckling. Consequently, the polygonal hollow section (PHS) which approximates an oval hollow section (OHS) and a rectangular hollow section (RHS) was proposed. Previous studies have shown the PHS has almost four times the rotational capacity of comparable RHS and the potential to minimize local buckling in thin-walled hollow sections. However, these studies only compared the PHS to RHS via four-point and three-point bending tests. As a result, a series of experimental cantilever bending tests using PHS and RHS beams were completed. The purpose of the cantilever tests was to compare the bending moments, stresses, strains and deflections of the PHS and RHS beams. The results showed that in the linear range, the PHS beams experience higher deflections than the RHS beams due to their lower moment of inertia, especially for the larger PHS and RHS beams. However, for the smaller beams that experienced higher strains in the regions of higher bending moments, the results showed that the PHS beams experienced less deformation than the RHS beams. It is likely that the bends of the PHS helped minimize ovalization of its cross-section, which minimised deformation. Furthermore, the results showed lateral torsional bending is not significant for hollow structural section beams as the lateral deflections recorded at the top and bottom of all the beams during the bending tests were minimal, <2 mm.