Efficient HSS Connection

[streng9999]

I have to build out a cantilevered platform with HSS members and am thinking about the best way to make the connections at two locations - HSS to HSS and HSS to channel.
I'm using a Vertical HSS6x6x3/8 for a workable flat of ~4/25" and and HSS 4x4x3/8 for the beam.
I have a factored shear of 3 kips and a moment of 12 kip-ft at the end of the HSS 4x4.

1. Is analyzing the HSS4x4 to HSS6x6 weld using the elastic method acceptable or do I need to analyze it as per AISC K4.1? Using the section properties of a 5/16" 4x4 square weld works but K4.1 doesn't explicitly mention this arrangement.
2. Do I need a seat angle where the HSS4x4x connects to the HSS6x6 for extra stability?
3. For the HSS6x6 to the MC I was thinking of a plate welded to the HSS 6x6 and bolted to the channel. I've never done a combined welded/bolted connection before though so not sure if there's anything I have to watch out for.

 

[dik]

That's about as simple as it gets... for your cantilevered 'stub', you can weld an end plate to it and attach at the edges of your main HSS member if the moment is high... else you can easily design the face of the HSS for a moment from the stub.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[streng9999]

Agreed, I looked at that and the HSS 6x6 was designed as per both AISC Chapter F and K3.2 so it works for the moment from the stub.
For the HSS4x4 all-around weld, do I need to take any reduction in the weld to account for the radius even if the workable flat is more than 4"?
I can't find a good reference or example for this type of connection - DG24 doesn't have too much on it and neither do the AISC examples.
The elastic method is supposed to be conservative and the weld works as per that but AISC K4.1 reduces the capacity of the weld lines significantly by using the effective weld length so not sure how to proceed.