Effective methods for the analysis of steel structures with strain-softening behaviour

In this paper two methods are presented for the solution of steel structures taking into account softening phenomena. This behaviour results from the coupling of local buckling and lateral-torsional buckling phenomena and leads to a nonconvex function of the potential energy of the structure. The problem is formulated on the rigorous mathematical background of hemivariational inequalities. Both methods reduce the nonconvex minimization problem to a number of convex minimization subproblems which are treated numerically with the methods used for the solution of the classical plasticity problems. In this sense, both approaches proposed here can be understood as extensions of the classical plasticity theory which is familiar to structural engineers. (C) 1997 Elsevier Science Ltd.