Answer:
In the case of biaxial loading, it may happen that the combined internal forces do not lead to the maximum stresses. Therefore, the "Calculate stresses from single load cases in RC, then combine stresses according to RC criteria" option is set by default. Please check in the Details dialog box to see if this calculation method has been set.
Further information about the stresses of result combinations can be found in the RF‑/STEEL manual.
