Directional increase for fillet welds on moment connections 3

[YoungGunner]

I've seen some chatter that we can't use the directional increase for moment connections for HSS members on base plates, but the only provision I know of is in K4 of the specification, but the context of that section doesn't seem to be referring to base plates. I'm also wondering if that directional increase could be applied to W-shape columns. I saw someone ask on another thread and they were never answered.

Also wondering how much of the HSS column you would consider as effective in resisting the moment. Just the furthermost flange? Or the webs as well?

 

[271828]

Design Guide 24, Page 56 seems to agree with not using the directional increase. Check that out.

 

[271828]

But wait, the Companion to the AISC Steel Construction Manual, Design Examples Version 15.1, Example K.9, Page K-43 DOES use the increase.

Conceptually, I don't see why it wouldn't apply.

 

[WillisV]

Recent testing shows that this condition twists the weld about its root (i.e. a one sided fillet weld on an axial plate type condition) so to combat this issue the directional weld increase is not permitted for rectangular HSS in the 2022
spec.

 

[dhengr]

WillisV:
I agree with you, but I’d say it a little differently. That loading, on that weld, tends to cause a tension stress field perpendicular to (and across) and prying on the root of the weld. The root of that weld is its weakest point w.r.t. type of loading, where there is a crack starter btwn. the two pieces of material, actually two, one on each piece of material at the weld, and some lack of penetration and fusion. I would certainly not change the weld size on that face, that would just confuse the welder, and give you a 50/50 chance of getting the wrong size in the wrong place.

 

[concepto.ed]

Take a look at this article from the Steel Tube Institute:

Link

 

[dik]

With HSS, because you cannot weld the inside of the tube, the weld is loaded eccentrically... Packer, etc. all recommend that directional strength not be included.

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

-Dik

 

[YoungGunner]

Thank you for your responses. I can get behind not using the increase on an HSS where the weld is only located on one side of the wall, but what then about wide flange columns? If we use a double fillet on the flange, would the increase be used or not?

 

[ProgrammingPE]

...what then about wide flange columns? If we use a double fillet on the flange, would the increase be used or not?

You can still use the directionality factor for wide flange columns (especially if you have double fillets). The change in AISC 360-22 says that 1.0 must be used "For fillet welds to the ends of rectangular HSS loaded in tension."

The issue with HSS is that the walls can be very thin with large distances between the stiffening elements (high b/t values). This means that they will rotate more due to the eccentric tension cause by one sided welding. The article from the Steel Tube Institute says that the effect of single sided welding was not as severe for round HSS, which is likely because their curved shape makes their walls stiffer.

Structural Engineering Software:

http://www.structuralcentral.com/tools/steel-connection

Structural Engineering Videos:

http://www.youtube.com/structuralcentral

 

[dik]

The STI has a freely available HSS connection design program. Membership is relatively inexpensive and the benefits from their webinars is great, including free access to their excellent publications. Seriously consider joining this org...

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

-Dik