HSS to HSS Welded Connection - Side Matched Dimensions

[RFreund]

What is the "best" way to identify and calculate an HSS to HSS weld where the HSS dimensions match?
Will this follow a PJP T-Tubular connection? If so I'm a little confused on how to calculate this. Also the figure in table 8-2 page 8-64 in my 2010 edition gives a "C" dimension and also show a 1.5t.b or as required to flush out dimension and I'm not sure what this is for. Is this something that I designate or is that just part of the prequalified weld?

EIT

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[JAE]

Two sides will have flare bevel groove welds. The effective throat would depend on the size of the tubes and the resulting radius of the tube corners.

The other two sides would have fillet welds.

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[RFreund]

So even if there is a gap between the side and the radius, this would still be a flare bevel groove weld? Is there a limitation on this?

Thanks, btw.

EIT

http://www.HowToEngineer.com

 

[JAE]

I didn't notice that you were actually stating there'd be a root opening.

The pre-qualified weld for this is in Table 8-2 of the AISC manual (13th Edition) for a P10 weld
That shows the root opening R = 0 but has an "As Detailed" tolerance of +1/16" and a "Fit Up" tolerance of +1/8" / -1/16" from the Detailed dimensions.

Those apply to SMAW, FCAW and GMAW but not SAW welds.

You could further research this in AWS D1.1 - I have an old copy of this where this is mentioned in sections 3.11.3 and 3.12.3.

I suppose that if you had to have a wider gap then a backer rod or plate might be used but I'd have to ask a qualified welder about that.






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[dik]

I often size members such that one is smaller than the other so a fillet weld can be used all around... also typically size HSS so that it is about 70% of capacity, so welds don't have to be CJP welds.

Dik

 

[racookpe1978]

Well, in this case, the "curve" of the HSS creates the CJP "prep" automatically - assuming the welder/fitter grinds the joint clean and bright. If not, then it isn't going to develop anything but weight.

 

[SwinnyGG]

That shows the root opening R = 0 but has an "As Detailed" tolerance of +1/16" and a "Fit Up" tolerance of +1/8" / -1/16" from the Detailed dimensions.

HSS corner radii are almost never (I'm saying almost never instead of never... just in case. But really, it's never) SMALLER than 2t.

Meaning that for same-size HSS welded tee connections, there will always be a root gap of, at minimum, the base metal thickness.

So unless you're buying HSS sections with t <= 1/8"..........

 

[JAE]

Yep - that is true.

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[RFreund]

@jgKRI - That's essentially what I was getting at. The radius creates the gap.

So... I think I'm back to where I started. Is this still a pjp weld? Does it need a backer? The T-Tubular connection shows no backer rod.

Thanks again for the replies.


EIT

http://www.HowToEngineer.com

 

[dik]

Is this still a pjp weld?

Yes... that's why I typically design to about 70% capacity... it generally less costly.

Dik

 

[JAE]

The small gap/root isn't typically an issue for these welds and the root/gap isn't that large for most moderate sized tube walls.
Here's a series of drawings of a tube-to-tube connection with 1/4" walls and 1/2" walls. AISC provides a variation in bend radius
from 1.5t, 2t, and 2.25t depending on the design function.

In most of these cases the root is less than or equal to the Fit-Up tolerance.

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[KootK]

I'm glad to see this question asked as it's something that I've wondered about often myself. For architectural and, occasionally, practical reasons it's pretty common to use the same HSS width for both members. I think that the question still remains: what is the accepted procedure for specifying the weld, executing the weld, and assessing the capacity of the weld?

I've had QC problems in the past with flare bevel welds even when there was no gap. I'd have to think that QC on this would be worse. Additionally, without intentional gapping and a very specific order to the weld deposits, I'd think that this condition would be ripe for lamellar tearing issues. My inclination is actually to disregard the capacity of this weld even though it's probably the stiffest path for much of the load to travel.

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.

 

[MotorCity]

In my mind, if there is a gap wide enough to require backing, it is a CJP weld because the weld extends to the full thickness of the piece. If there is no gap or a gap small enough not to require backing, it seems like it would be a flare bevel weld. Not sure how big of a gap can be accommodated without backing.

 

[JAE]

MotorCity - our in-house welding guy sort of scoffed at my concern over the root opening. He indicated that qualified welders would have no problems with these sizes of gaps, despite the As-detailed and Fit-up root limits shown in the pre-qualified P10 welds. He thought the weld would be able to bridge the gap without problems and without needing a backer.

If a backer was deemed necessary, the other approach would be to cope the tube side walls to create a tighter fit....similar to round pipe-to-pipe connections.

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[XR250]

I have seen my fabricator do the coping as JAE noted.

 

[sandman21]

I have never run into an issue with the gap, however the ASIC manual figure 8-20 shows conditions to address the issue.

 

[SwinnyGG]

These welds are relatively easy compared to most welds with gaps, because at each end where the weld would typically start, there is a 'backer' of sorts- the tube wall running away perpendicular to the weld. SO there's sort of a 'true flare bevel groove' weld at each end with weld length equal to wall thickness. A trained monkey can start a weld there. A skilled welder can draw that weld across the gap very easily.

How that relates to code compliance and WPS development and all of that... I don't know. I'm a non-SE but I spec a LOT of stuff made from welded HSS.

 

[RFreund]

Fig 8-20 (which is actually 8-18 and 8-19 in my 2010 edition) seem to address this to a certain degree. On my page 8-23, section "Welding Considerations for HSS" there is a sentence that reads: "However, when the corner radius increases due to wall thickness or manufacturing tolerances, the root gap may need to be adjusted by profile shaping, building out with weld metal, or by use of backing." My question is:
[ol 1]
[li]Do I need to know when this is required? Or is this part of the WSP and taken care of by the fabricator?[/li]
[li]If yes, do I need to spec/show that?[/li]
[/ol]

Based on the responses and the figure 8-18 & 8-19 (my 2010 edition), it seems that this would be specified as a flare bevel weld. In which case how would I properly show the effective throat and/or what should be used for the capacity of such weld?

Thanks again!


EIT

http://www.HowToEngineer.com

 

[JAE]

The effective throat (E) in AISC Table 8-2 for a P10 is 5/8 x T.
With a larger root than specified in the table, you might consider a reduced value - perhaps 0.5T?



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[EZBuilding]

Although the discussions regarding these welds are very interesting, and something I've thought about in the past, I am surprised no one has question the need for the side welds. For typical storefront headers I've often found that a weld top and bottom is more than adequate. I've often provided tab plates top and bottom so there is a construction tolerance between header and jamb members.