First-hinge analysis for lateral buckling design of open thin-walled steel members

The study presents a numerical approach to first-hinge stability design of open thin-walled steel members with arbitrary internal forces including nonuniform torsion. A generally applicable numerical method for the evaluation of plastic cross-section resistance is presented. The applied optimization formulation allows for yielding due to the simultaneous action of normal and shear stresses according to the von Mises yield criterion. Specific considerations are necessary to account for shear stresses from uniform torsion. Unlike in the case of two-dimensional beam problems, the load-carrying behaviour of thin-walled beams under lateral buckling loading changes significantly when yielding starts. This leads to restrictions and specific procedures in the application of second-order beam theory with a first-hinge criterion, to the solution of 3-D stability problems.