A post buckling analysis program has been developed for two dimensional elasto-plastic frames using large displacement theory. The formulation is based on an incremental variational principle employing the total Lagrangian approach. A constant displacement length method in conjunction with the Newton-Raphson method is used for the solution of the finite element equations. A direction finding criterion for the incremental displacement has been suggested utilizing the information of the previous displacement. The resulting numerical algorithm is shown to be very stable for all the steps. Plastic deformation is considered by a layered approach where each layer is separately checked for its status. The material property is approximated by piecewise linear or parabolic functions. Several examples from literature are solved and compared with the existing or analytic solutions, obtaining almost the same results. Although a limited number of problems have been tested, the developed program is designed to be general enough for two dimensional frame problems.
