Predictive models for strength enhancements in cold-formed structural sections

Cold-formed structural sections are manufactured at ambient temperature and hence undergo plastic deformations which result in an increase in the yield stress and ultimate stress, but reduced ductility. This paper begins with a comparative study of existing predictive models to harness this strength increase. Modifications to the existing models are then made and an improved model is presented. Tensile coupon tests from the literature have been used to validate and compare the predictive models. A wide range of structural section types from both cold-rolling and press-braking fabrication processes and structural materials, including various grades of carbon steel and stainless steel, have been considered. gauge cold-formed structural sections. In pressbraking the sheet material is formed into the required shape by creating individual bends along its length. It is a semi-automated process used to produce open sections, such as angles and channels, in limited quantities. Air press-braking, where elastic spring back is allowed by over-bending the material, is more commonly adopted than coin press-braking, where the die and the tool fit into one another. Coldrolling is an automated continuous bending process in which the gradual deformation of the uncoiled metal sheet through a series of successive rollers produces the final cross-section profile. In case of tubular box sections, the flat metal sheet is first rolled into a circular tube and is welded closed. It is subsequently deformed into a square or rectangle by means of dies. The tube’s cross-section is initially circular whereas the cross-section at the end of the process is a square or rectangle with round corners. Finite element models with contact boundary conditions allow simulation of this continuous process, but are rather complex and time consuming and require sophisticated software.