Answer:
In RSTAB, it is also possible to determine plastic internal forces. To do this, you have to select a plastic hinge as a nonlinearity using the member properties (see Image 01). However, this does not include any interaction of the plastic internal forces. Another possibility is to set releases with nonlinear properties directly. However, with this method, you have to estimate beforehand where these hinges are formed.
RFEM provides the option to select a corresponding material model (see Image 02).