AISC Section Classification for Unistrut 2

[Ussuri]

I am looking at situation where we have some lengths of Unistrut being used for supporting light loads associated with some subsea controls. In some instances the Unistrut will be biaxially loaded with a UDL (0.13kN/m about minor axis and 0.82kN/m about the major axis) so instead of using their published loading tables I have just taken their section properties and intended to do some checks myself. The purpose of the exercise is to identify a limiting span.

The Unistrut is P1000 profile so is basically a 41mm x 41mm x 2.5mm thick channel with the toes of the channel flange turned back into a return.

I was looking at the section classification for the channel flange (Table B4.1b) and with a b/t = 16.4 the flange is classed as Non Compact. Which as far as I can see rules it outwith the scope of all the provisions of AISC Section F. I assume this is because all the standard US structural sections have Compact flanges.

Now the return at the end of the toe will provide a stiffening effect, so the straight b/t seems conservative and I wondered if h/t provisions (3.76 (E/Fy)^0.5) might be applicable. However, I couldn't find any guidance into how stiff a return needs to be before it would be considered effective?

Alternatively, are there provisions in the specification that I missed that relate to channels with a Non Compact (or Slender) flange?

 

[KootK]

You'll likely be better of using the cold formed steel spec, S136.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[TehMightyEngineer]

What KootK said. While you could probably use the AISC specification easily enough the cold formed steel spec is more applicable for this and should answer your questions.

Maine Professional and Structural Engineer.
(Just passed the 16-hour SE exam, woohoo!)

 

[JStephen]

The building codes are written to fit work normally done, and when you get into an oddball geometry, there's no guarantee that you'll find an answer in the codes. If it's a major item, you do finite element stuff, if it's a minor item and you're making a million of them, you do testing and/or finite element. If it's a minor item and you've just got a few, you make your best guess and upsize as required. In a lot of those cases, it'll be cheaper to add material than it will be to do the analysis to prove you don't need to.

 

[wannabeSE]

In the US, it is AISI S100

https://shop.steel.org/p/300/aisi-s...pecification-2012-edition-electronic-version.

Hand calculating effective section properties per AISI is not for the faint of heart. I am attaching the Unistrut table I like

 

[Ussuri]

Perfect. Thank you all.