Tube to Tube Moment 1

SteelPE · Friday at 3:02 PM

I have a project where the client has had the architect client has had the bright idea to have a fancy canopy project out from the front of the building. To add to the complexity, this canopy is to have AESS (architecturally exposed structural steel). One area requires a rectangular HSS to frame into a round column with a moment connection. I am wondering if anyone has any insight into figuring the capacity of this type of connection?

The code requires us to use AISC 360-16. I know Tables K4.1 and K4.2 handle tube to tube moment connections, but it doesn't cover this exact instance

K4.1 = round HSS to round HSS
K4.2 = square HSS to square HSS

I am currently trying to convince the client to move away from the proposed framing.... but he has been a bit grumpy for the past week or so and has dismissed me at every turn. I honestly think this little canopy is going to have a huge price tag and I will be redesigning it in a few months.

Any help would be appreciated

bones206 · Friday at 3:25 PM

I always end up spending 5x design time on these fancy canopies compared to the buildings attached to them

I would go with the provisions for plastification of round main member. I *think* the equation would be still be applicable even with a rectangular branch member.

Ussuri · Friday at 3:25 PM

You could look at the CIDECT Design Guides. Design Guide 1 for CHS chords and Design Guide 3 for RHS chords

Also Eurocode 3 EN 1993-1-8 could be a reference

KootK · Friday at 4:53 PM

You might treat the moment as two line loads imposed by the square HSS flanges on the round HSS walls. Shear goes through the square HSS side wall welds and is probably of little consequence.

SteelPE · Friday at 6:09 PM

bones206 said:
I always end up spending 5x design time on these fancy canopies compared to the buildings attached to them

I would go with the provisions for plastification of round main member. I *think* the equation would be still be applicable even with a rectangular branch member.

Yes, that is somewhat what I am going to have to deal with on this one. The ole "it has a small canopy on the front" trick.

How would you treat Db in this scenario. The branch member is not a square but rather a 10x6 tube. I can take an average of the two sides (8 in) or use 90% of the depth (9").

I tried to download the CDICT guide, but for some reason the website says they are no longer allowing downloads of their guides (wonder if this was a DOGE cut???).

HTURKAK · Friday at 6:21 PM

You download from the link. https://drive.google.com/drive/folders/1fF9XYhPEPbgpUPfHuyqn6g3UPpcDhSXe

The following doc. gives some insight regarding Eurocode approach.
I would consider the RHS as open section and yield lines then check for each failure mode.

bones206 · Friday at 11:15 PM

SteelPE said:
How would you treat Db in this scenario. The branch member is not a square but rather a 10x6 tube. I can take an average of the two sides (8 in) or use 90% of the depth (9").

It’s a judgment call, but I don’t think using 10” would be unreasonable for strong axis bending.

Kootk’s idea to treat the top and bottom flanges as standalone transverse plates welded to the round column is a good one. This would be checked with K1-1 for local wall yielding. Would be interesting compare the results of both approaches. Either way just make the column walls thick enough that these limit states are not even close so you can move on. Maybe you can save cost in another aspect of the design.

jhnblgr · Saturday at 12:19 AM

Look at cantilever sign structures for guidance, the loads would be similar in nature. What they found is fatigue typically controls connections so keeping stress low is key. AASHTO code overhead signs and luminaries

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