Predictive models for material properties of cold-formed conventional steels in the corner region

Current North American Specification AISI S100-16 provides design formulae to predict the yield strength of cold-formed steels. These design formulae were proposed on the basis of Karren's experimental works in 1967. The measured yield strength of the parent materials in Karren works only varies from 203 MPa to 315 MPa (29.5 ksi to 45.7 ksi). This paper aims to extend the validity of the design formulae to a wider range of material and geometry parameters, and a comprehensive material test program was carried out to further investigate the cold-forming effects. Nine batches of conventional steel plates were used, with the nominal thickness ranging from 2 mm to 5 mm and the nominal value of yield strength covering 235 MPa, 275 MPa and 355 MPa. A total of 81 flat coupons extracted from parent materials and 144 corner coupons sectioned from cold-formed corners were tested, with measured original yield strength up to 431 MPa and enhanced yield strength after cold-forming up to 625 MPa. These cold-formed corners were press-braked with different punch radii and included angles to achieve various geometric configurations which result in different levels of plastic deformation. The test data generated from this study were used in conjunction with data collected from the literature to establish a comprehensive database. Subsequently, predictive models were proposed to calculate the strength enhancements on the yield strength and ultimate tensile strength, and the loss in ultimate strain and elongation at fracture. It is shown that the proposed models can produce accurate predictions on the material properties of cold-formed steels.