Design optimisation for cold rolled steel beam sections with web and flange stiffeners

This paper presents the analysis and design optimisation of the cold rolled steel sections for flexural strength considering the effect of cold working exerted on the section during the roll forming process. The sections included channel and zed shapes with complex longitudinal web and flange stiffeners. Nonlinear Finite Element (FE) modelling was developed to model the flexural strength of the channel and zed beams and validated against the four-point bending experiments for these sections. The material properties of steel at the section’s flat parts, corners, and stiffener bends were obtained from tensile tests and were incorporated into the FE simulations to account for the true material properties at these regions due to the cold working during the roll forming process. The strength enhancement at the section corners and stiffener bends obtained from tensile tests were also compared with the predicted values from design standards. The section strength was then optimised using FE modelling results based on the Design Of Experiments (DOE) and response surface methodology. Optimal designs for the channel and zed sections with maximum strength in distortional buckling could be obtained while changing the stiffeners’ position, shape, sizes, and considering true material properties at section corners and stiffener bends. It revealed that, for the two sets of channel and zed sections with the depths of 145 mm and 170 mm, the optimal designs provided up to 43% and 39% increase in flexural strength for the channel and zed sections, respectively; however, when the true material properties at the section corner and the stiffener’s bend regions was included, the increase in flexural strength increased up to 50% and 41%, respectively. Including flange stiffeners to the sections with longitudinal web stiffeners generally increased further the section strength. However, the levels of increase were largely dependent on the section depths and material properties.