Moment Frame Question

[XR250]

I have a moment frame for a screened porch that is not working very hard. It is resisting mainly wind loads. It is a W10x22 beam on top of an HSS5x5. Based on the numbers, fillet welds will work. Any reason I would have to use full-penetration welds?

 

[EngDM]

If the loads are low you don't need CJP welds. Just make sure when sizing your welds you are taking an appropriate workable flat length; typically for HSS the area by the corner radius is neglected. Not sure off hand what AISC uses/prescribes but I've used B-2*(2*t_nom) in the past.

Instead of a CJP you could specify a PJP groove weld and you wouldn't necessarily need a backer bar. But IMO fillet is king here.

 

[Flotsam7018]

Nope. Use fillets whenever you can, the fabricator will appreciate it. Especially on HSS, which is a real PIA for CJP welds.

The corner radius per AISC is 2.25*tnom. Using only the workable flats for the weld group properties has always irked me, though it is conservative and fast.

 

[KootK]

Also no to the CJP. For something like this, I feel that your main concern is joint rotational stiffness. To that end, I would see more value in a pair of partial height stiffeners over the post walls than the CJP. Detailed this way, I think that it would make sense to only rely upon the welds under the stiffeners for a quick and dirty design.

 

[XR250]

Thanks for everyone's insights

 

[sandman21]

The workable flat is not the exact as ASTM A500 allows for a greater radius than AISC assumption in the tables. Some that show a workable flat will not have a "flat" with the larger radius vice versa

 

[EngDM]

The workable flat is not the exact as ASTM A500 allows for a greater radius than AISC assumption in the tables. Some that show a workable flat will not have a "flat" with the larger radius vice versa

One of the many reasons why if I see a substitution from G40.20 to A500 it's a no.

 

[lexpatrie]

My feel is full penetration welds are more for high seismic (pre-qualified connections?) than other tasks.

Is the intent here to directly weld the column HSS to the bottom flange of the W10x22? That sounds like a field weld on a screened porch.

If it's not being too much demand, is there a way to get base fixity and consider the HSS to beam as pinned and still get it to work?

 

[XR250]

Is the intent here to directly weld the column HSS to the bottom flange of the W10x22? That sounds like a field weld on a screened porch.

Yes. I know the fabricator. He is fine with it. The arch. wants to see steel and does not want to see bracing. The aspect ratio of the porch is such that i don't want to cantilever the whole mess of the house.

If it's not being too much demand, is there a way to get base fixity and consider the HSS to beam as pinned and still get it to work?

I am doing a fixed base as well to get better performance as it is a double story. Moment frame/fixed base to brace the floor system and then more HSS flag poled up to brace the roof.

 

[lexpatrie]

(Not my drawing) This is an HSS 5x5 (a 5x5 HSS?) going to a W8x13. Going into an existing 2x6 wall for context.

 

[XR250]

Not a fan of this detail due to the flexibility of the HSS walls. Figuring out the stress on the weld of the flange plate would require FEA.
That is why I have the beam on top of the column.

 

[TRAK.Structural]

Agree with others that fillets should be fine here if it's and R=3 system.

Honestly I think something close to lex's detail would be more stiff than the beam sitting on top of the post (even considering hss sidewall flexibility). Unless you are using some stiffener plates in the beam I would think the flange would flex also.

 

[KootK]

I had similar thoughts regarding stiffness. My only beef with Lex's detail is that I feel that it is sometimes more erection friendly to go over the top when you're talking about something that may be erected without the benefit of a crane etc. Unless the thing can be assembled on the ground and tilted up.

The detail below would be my goto for a situation like this. The connection does force the post inboard from the wall ends a bit which can be be a deal breaker depending on the arrangement. And I could probably be sold on a single stiffener with the right design checks in play.

@XR250: wrt to the welding being proposed, would that be done as overhead welding?

 

[human909]

lexpatrie's detail is my standard detail for residential portal frames which normally are using channel. The channel is comparatively narrow for it's depth and the HSS wall thickness to width is reasonably high so the walls aren't particularly flexible. Typical connections would be to HSS that would be 75x5 or 90x6. Or even better I just use the channel for the column as well. A 75mm or 90mm wide channel will fit into a typical wall frame.

Oh and as far as the original comment goes. I almost NEVER use full penetration or partial penetration welds. Fillets are so much cheaper and easier and more reliable in the absence of good quality control.

 

[XR250]

Agree with others that fillets should be fine here if it's and R=3 system.

Honestly I think something close to lex's detail would be more stiff than the beam sitting on top of the post (even considering hss sidewall flexibility). Unless you are using some stiffener plates in the beam I would think the flange would flex also.

I am showing stiffener plates.

 

[XR250]

@XR250: wrt to the welding being proposed, would that be done as overhead welding?

Yes. The fabricator says he is ok with it. I keep the column flush with the edge of the beam and run a plate up that encompasses the left face of the column and end of the beam web and top flange. The Arch. like the flush look and it seems a bit easier to fabricate.

 

[phamENG]

If you're flush on the sides then I'd want at least a PJP all around. I only do that type of moment connection with a weld-all-around between the column and the cap plate (beam, in your circumstance as you won't be bolting it).

 

[EngDM]

If you're flush on the sides then I'd want at least a PJP all around. I only do that type of moment connection with a weld-all-around between the column and the cap plate (beam, in your circumstance as you won't be bolting it).

I think he's flush only on the end of the beam. So in that case he could weld column>plate>web/flange of beam.

 

[XR250]

Like this...

 

[EngDM]

Like this...

View attachment 2565

A part of me winces specifying a 3/16" weld for a moment connection, even if it is good enough in strength.