Answer:
Currently, the plasticity for 1D elements only works in relation to the normal stresses in a member. This means that only the interaction between an axial force and a moment is possible. The shear force interaction is not taken into account. Furthermore, the stresses due to shear force are only calculated elastically.
When applying the plastic material model, it is also important to ensure a sufficient division of the elements since a cross-section is generated internally at each Gauss point on the member element, where the stress is calculated and the stiffness is reduced to the redistribution of internal forces, if necessary. For example, when increasing the number of divisions, the model may become unstable, as the redistributions of stresses can no longer be performed, and thus loading in the cross-section is too high.
We generally recommend using a division of "50" for member elements when using the plastic material model (see the image).
