A NONLINEAR BEAM FINITE-ELEMENT FOR THE POSTBUCKLING ANALYSIS OF PLANE FRAMES BY KOITERS PERTURBATION APPROACH

A nonlinear finite element of plane beam oriented to Koiter's perturba tion analysis of frames is presented. The locking problem arising in t he calculation of the post-critical curvature is thoroughly examined a nd solved at the continuum level, by means of a suitable definition of the kinematic settings. The proposed strain measures are Lagrangian a nd rationally founded (geometrically exact). The exact solutions of th e critical problem have been chosen as shape functions of the finite e lement, so obtaining an immediately convergent finite element in the c alculation of the critical load and of the post-critical slope.