Seminar - Jianjun (Kevin) Ye - Behaviour of High Strength Steel Sections with Low Strain Hardening

Wednesday, November 8, 2000, 3 - 4 pm
Civil Engineering Lecture Room 3

Abstract

Steel with yield stress usually have little or no strain hardening in the strain-stress curve, and low ductility unlike conventional structural steel which is highly ductile and strain hardens so that the tensile strength to yield strength ratio, which is the conventional measure of strain-hardening, is about 1.5. For high strength steel, the ratio is often close to1.0, especially for thin cold-reduced steels with yield stress equal to 550 Mpa. Strain hardening is important in the stability of thin-walled sections and so the high strength steels are likely to have their stability significantly affected by lack of strain hardening. The main aim of the research project is to investigate the stability of high strength steel sections to determine the influence of the lack of strain hardening on their capacity to resist buckling, particularly in the inelastic range.

The new standard AS/NZS4600 for Code–Formed Structures and the new American Iron and Steel Institute(AISI) Specification for Code–Formed Structural Members has limited the design stress for high strength steel to 75 percent of their yield stress or tensile strength as applicable, mainly due to the lack of knowledge on their structural behaviour. A major objective of the project will be to determine whether the 75% limit on yield stress is valid for the thin AS1397 steels, and if not, whether it can be increased, and to what extent.

The research program consists mainly two components. My colleague Mr. Demao Yang is working for part (a)Experimental testing of cold-formed sections. I am working for part (b)Theoretical modeling using the finite element nonlinear analysis including large deformation and material plasticity. The experimental data becomes very important in calibrating and implementing the finite element analysis. Once this has been performed, the finite element analysis will be used to extend the range of test data, and to investigate the effect of changing variables, such as stress-strain characteristics, residual stresses, geometric imperfections and section geometry.