A distributed plasticity beam‐column finite element with interaction among all stress components

Abstract The fiber model evaluates the normal stress at a number of points over the section following the plane section assumption and, by integration, axial force and bending moments. The interaction with tangential stresses is neglected due to the inaccurate tangential strains of the kinematics. This work presents a generalized fiber model capable of considering interactions among all stress components. A preliminary cross‐section analysis, based on the Saint Venant problem, provides the 3D strain as a function of the section generalized strains. This field, accurate also in the inelastic case, is exploited to impose at each section point a 3D von Mises elasto‐plastic law, obtaining by integration all the resultants and moments with a full interaction. Non‐uniform warping is also easily included. The section model is implemented in a mixed 3D beam‐column finite element with equilibrated stress field, accurate with a minimal mesh. Numerical tests show the excellent prediction of the proposal compared to analytical and solid FEM solutions also for structures not flexure‐dominated. Its efficiency, on the same order as a standard fiber model, makes the approach suitable also for large buildings.