Design of direct-formed square and rectangular hollow section beams

Abstract

A complementary experimental study showed that the flexural member design rules in the North American steel design standards (AISC 360–16 and CSA S16-19) can be excessively conservative for direct-formed regular- and high-strength steel square and rectangular hollow sections (hereinafter collectively referred to as RHS). It was also found that post-production hot-dip galvanizing can further improve member flexural behaviours through effective reduction of cold-forming-induced residual stresses. In this study, the experimental results of 22 full-scale beam tests from the complementary experimental study are used to validate non-linear finite element (FE) models. The FE models are developed using previously measured stress-strain relationships, residual stresses, and geometric imperfections. A subsequent parametric study including 788 beam models is performed to cover extended ranges of cross-sectional dimensions. The applicability of the existing slenderness limits and flexural design formulae are examined using the experimental and numerical data. The results justify the use of less stringent slenderness limits and higher design curves for direct-formed regular- and high-strength RHS beams (untreated and galvanized). Modifications to the existing design rules are proposed. Based on reliability analyses, the modified approaches are proven accurate and provide adequate safety margins.