Answer:
Even if the description of the add-on modules is very similar, the calculations performed are different.
RF-/STEEL
This add-on module performs a general stress analysis by calculating the existing stresses and comparing them with the limit stresses. The design checks are performed elastically and do not depend on any standard.
RF-STEEL EC3
This add-on module, on the other hand, performs all typical design checks of ultimate limit state, stability, deformation, and fire resistance for steel members according to Eurocode 3 (numerous National Annexes are available). There is a range of module extensions available within this add-on module. These include: warping torsion analysis, plasticity analysis, design checks for cold-formed sections.
Comparison of Both Add-on Modules
The results of RF‑/STEEL can be compared with the results of the cross-section design of RF‑/STEEL EC3.
Why the results can differ is explained in FAQ 003489.