Residual stresses in cold-formed steel sections and their effect on column behaviour

This thesis is concerned with the theoretical modelling of the manufacturing process of press-braked carbon and stainless steel sections for the prediction of the resulting residual stresses and equivalent plastic strains. The residual stresses in such coldformed sections are derived from two sources: the coiling, uncoiling and flattening process (referred to simply as the coiling-uncoiling process) and the cold-forming process. A series of analytical solutions are presented in this thesis to predict the residual stresses and the associated equivalent plastic strains in steel sheets as a result of cold bending, covering both processes. These solutions are verified using finite element simulations of cold bending of steel sheets. For the modelling of cold bending of stainless steel sheets, a new stress-strain relationship was established to overcome significant deficiencies of existing stress-strain relationships.; On the basis of these analytical solutions, two alternative approaches for the prediction of residual stresses and equivalent plastic strains in press-braked sections are presented and verified: (a) a finite element-based method in which a finite element simulation of the cold-forming process is carried out with its initial state being defined by an analytical solution for the coiling-uncoiling process; and (b) a complete analytical model in which the residual stresses and equivalent plastic strains from both processes are given by analytical solutions. A parametric study employing the finite element-based method was conducted to study the effect of forming parameters on the resulting residual stresses in cold-formed sections. The complete analytical model provides an attractive approach for defining the initial state of a section in a column nonlinear buckling analysis.; The thesis next presents an advanced numerical approach to predict the buckling behaviour of cold-formed columns in which the effect of the manufacturing process is explicitly and accurately accounted for. In this approach, the complete analytical model for residual stresses is employed together with an appropriate imperfection model. Using this finite element method, the effect of cold work on buckling behaviour was examined. (Abstract shortened by UMI.)...