Why Etabs is classifying HSS 5x5x5/16 as non compact section?

[vatsalS]

I have assigned hss 5x5x5/16 section at braces in an OCBF system. In detailed report, etabs is classifying the section as a noncompact section which is not true per aisc 360-16 table E4.1. Also, it is defining it as moderately ductile as per aisc 341-16 table D1.1 Which is ok. But if the section is moderately ductile then it should satisfy the criteria for compact section as its b/t and H/t limits are higher than ductile criteria.

 

[dik]

No idea? bug? ignore blue highlighting.

Class 1 b/t <= 22.45, your section b/t = 16, nearly all HSS sections are Class 1 sections in flexure.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[ProgrammingPE]

I'm guessing a bug as well. The section is definitely compact. The flexural capacity is equal to plastic yielding (Mn/Ω = Fy*Z/Ω = 46 ksi * 9.16 in³ / 1.67 = 252 in-kip = 21.0 ft-kip) so the results still appear to be correct, regardless.

(Also, Ry should be 1.4 for A500 Gr. B.)

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[dik]

Our HSS are fy = 50ksi... 350MPa... sightly different limit on b/t.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[JoshPlumSE]

Have you checked the AISC 341 compactness for OCBF's?

I'm just asking because there are different compactness limits for AISC 341 and AISC 360. I tend to use the terminology "Highly Ductile" and "Moderately Ductile" for the AISC 341 limits. But, that's newer terminology only present in the 2010 and 2015 codes.

I don't know if ETABS uses compactness for those limits. Because in the 2005 (and prior) codes, the the term "seismically compact" was used. Therefore, we were left with an 'in between' designation where something was NOT seismically compact per 341, but may have been compact per 360. I'm not sure how that would have been referenced.

Caveat:
I'm not a true "expert" in ETABS, and I haven't tested out these concepts (playing with different compactness levels) in ETABS to test exactly how it's reported on the output. However, I do work for CSI (the company that produces ETABS). So, any opinions I give should be taken with the understanding that I have some inherent bias on the subject.

 

[dik]

Just a Canadian code guy... with a little venture into the AISC as it serves me... I cannot imagine that different codes would be 'that far off'... b/t = 16 vs. b/t = 22. I could see 22 vs maybe 21, or something of that ilk.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik