Moment gradient effects on load-carrying capacity of stainless-steel SHS and RHS beams

Abstract

A comprehensive experimental and numerical study on the cross-sectional load-carrying behaviour of cold-formed stainless-steel square and rectangular hollow section (SHS/RHS) beams under the effect of moment gradients is presented in this paper. Three four-point bending tests and six three-point bending tests were first conducted on cold-drawn austenitic stainless-steel SHS beams with various moment gradients. Digital image correlation (DIC) system was employed to monitor the strain development during the tests. Validated finite element (FE) models were developed to simulate the structural performance of cold-formed SHS and RHS beams and were subsequently used in a numerical parametric study to generate a comprehensive dataset covering a wide range of cross-sectional geometries, materials, and moment distributions. The results showed that the bending moment capacity of stainless-steel SHS and RHS beams is enhanced by the presence of moment gradients, with the magnitude of enhancement being highly related to the cross-section slenderness. This study refines and extends a recent design proposal that introduces a parameter to capture the effect of moment gradients on the local buckling capacity of beams, aligning with EN 1993-1-1:2023, to stainless-steel SHS and RHS beams. The effectiveness of the proposal under the framework of prEN 1993-1-4:2023 was evaluated using experimental and numerical results. The approach was found to consistently provide more accurate resistance predictions than the current EC3 design rules for stainless-steel SHS and RHS beams under combined shear and moment. The reliability of the proposed method was further validated through statistical analyses in accordance with EN 1990:2023.