Strength and ductility of steel members based on post-yield stability and collapse behaviour

The inelastic stability problem has numerous applications in structural design of buildings, bridges and industrial structures. Plastically designed members have been in use for a long time but a new emphasis is being placed today on the extent of ductility that they have to possess, in the form of rotational and deformation capacity especially in seismic design applications. With the emergence of the new, high strength steels, and with the advanced methods of steel fabrication that are producing sections with different tolerances, imperfections, and residual stresses, design standards have to be reassessed and adapted to reflect these changes.; This research study presents an analytical finite element investigation into the behaviour of wide flange members loaded beyond their yield capacity as columns and beams and examines local and lateral buckling behaviours and their effects on strength and deformation capacity. The study involves an area of research for which the classical theory is very complex. This analytical study is based on a nonlinear large-strain/displacement finite element model that was developed in this research using ANSYS. Emphasis is placed on examining the rotational capacity and local buckling behaviour of wide flange flexural members that exceed current Class 2 (compact sections) requirements.; The validity of the model is tested by comparing the results of the analyses with existing experimental data and the results from a program of tests conducted on short columns and carried out under controlled conditions and careful measurements by the author. The ability of the model to reproduce the full range of experimentally observed behaviour of columns, beams and beam-columns is clearly demonstrated. The parameters that affect the local buckling behaviour of compact and plastic sections are assessed and qualified. Comparisons of analytical results with existing code requirements are presented with recommendations for changes in design codes and standards.