The evaluation of the maximum level of load that any 2D framed structure can undergo,
before plastic collapse or buckling, is addressed in this paper. The analytical approach,
based on a beam element with elastic behaviour except on its ends, uses an incremental
approach to determine when changes appear due to plastic behaviour. When the
combination of axial force and bending moment in any cross-section reaches the plastic
function, that section is considered to yield suddenly and relative displacements can appear
because of the yielding. The model includes the traditional plastic hinge, which only
considers relative rotation due to the effect of the bending moment. The sequential loading
and yielding reduces the stiffness and stability of the frame, which is computed and
compared with the classic plastic methods of analysis.
