Design optimisation for cold rolled steel beam sections with complex stiffeners considering cold working effects

This paper presents the analysis and design optimization 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. The section strength was then optimized 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 material properties at section corners and stiffener bends. It revealed that, the optimal designs provided up to 13% and 17% 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 20% and 23%, respectively.