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002694
2019-03-27

Question

In an older model of RFEM 4 or RSTAB 7, I designed a SHAPE‑THIN cross-section or a general cross-section in STEEL EC3. At that time, cross-section Class 1 or 2 was determined. Now, I have opened the model in RFEM 5 and the cross-section is only classified as Class 3 or Class 4. Why? Was the design more cost-efficient at the time?

Answer:
The design of general cross-sections or SHAPE‑THIN cross-sections is always performed elastically in STEEL EC3; that is, according to Class 3 or Class 4. Since the interaction conditions are limited to certain cross-sections, plastic design is not possible for all cross-section shapes. In RFEM 4 and RSTAB 7, however, it was possible to classify a cross-section as Class 1 or Class 2, even though the subsequent design was carried out elastically.
To eliminate this ambiguity and for the sake of consistency, the classification has also been changed to cross-section Classes 3 and 4.
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