Influences of cold working on tensile and bending strength of cold roll formed steel sections contain complex folded-in stiffeners

This paper aims to study the cold working influences on material and structural properties of the cold roll formed steel sections contain complex longitudinally stiffeners under bending. Tensile tests on flat and curved samples extracted from the complex stiffeners of channel and zed sections were conducted to investigate the change of material properties due to cold working during the roll forming process. The influences of cold working in the section flat regions, corners and stiffener bends were investigated and evaluated against some predictive models in literature studies. Nonlinear Finite Element modelling was developed to model the four-point bending tests to study the effects of cold working on the buckling and ultimate strengths of channel and zed sections. In the bending models, experimental material properties of section flat parts, corners and stiffener bends were implemented to search for the optimal shapes of the sections. Significant improvements were obtained for the section strength of the optimized sections in comparison to the original sections. Optimal shapes for the channel and zed sections with maximum strength in distortional buckling could be obtained while changing the stiffeners’ position, shape, sizes, and considering the effect of cold working. It revealed that, the optimal sections provided up to 13% and 17% increase in bending strength for the channel and zed section, respectively; however, when the effect of cold working at the section corner and the stiffener’s bend regions was included, the increase in bending strength increased up to 20% and 23%, respectively.We would like to acknowledge the University of Derby for providing the sponsor of this work [PGTA Studentship - E&T_14_PGTA_0717]. The tensile tests were carried out at the University of Sheffield