Evaluation of Lay's equation for plastic hinge location in steel columns
The current New Zealand steel structures standard has a provision that aims to restrict plastic hinges to develop only at the member ends. The equations in this provision were adopted from Lay’s PhD thesis which were developed not only to encourage yielding at the member end, but also to ensure sufficient member rotational capacity can be maintained. The accuracy of the end yielding criteria in Lay’s equations is examined using an analytical technique developed in this study. The analytical procedure incorporates nonlinear geometric and material effects by considering stability functions in conjunction with residual stress effects. It is found that the code equations are more conservative compared with the analysis results. A new equation to prevent yielding away from the member ends is proposed in the research project. This forms the basis for the proposed amendments to Clause 18.104.22.168 in New Zealand steel structures standard.