Behavior of Cold-Formed Steel Built-Up Sections with Intermediate Stiffeners under Bending. II: Parametric Study and Design

Abstract

Built-up sections were used in a wide range of constructional steel applications. The investigation aims to develop suitable design rules for cold-formed steel doubly symmetric built-up open and closed sections with intermediate stiffeners under bending in this study. These built-up sections have a sufficient number of connections either at the flanges or webs, depending on the sectional configurations. Followed with the experimental investigation and finite-element validation in the first part of this study, a numerical parametric study including a total of 113 different built-up section beams was conducted. The key parameters including the sectional shapes and slenderness as well as the different failure modes and structural behavior were examined. The experimental data, together with the numerical results were compared with the predicted strengths using the current direct strength method (DSM) in the North American Specification. The determination of elastic buckling stresses corresponding to different failure modes, mainly the local and distortional buckling, for beam members is a prerequisite for DSM. Simplified assumptions on the built-up sections were employed in determining the elastic buckling stresses. Furthermore, modified DSM equations for beams with different built-up sectional configurations were calibrated with the experimental and numerical data obtained from this study. The design strengths predicted by the recommended design rules exhibited good agreement with ultimate moments of the built-up open and closed section beams. A reliability analysis was also performed. It is shown that the recommended design rules for cold-formed steel built-up open and closed sections with intermediate stiffeners under bending is reliable.