CJP Beam Splice In-Place

[RPMG]

I specified a CJP field weld, and the detailer has pointed out that it requires a backing tab which can't be installed because there is an existing metal deck and slab above. Does anyone have a solution for this?

 

[jayrod12]

maybe flange plates on the underside of the beam designed to transfer your beam flange forces across the joint?

 

[Celt83]

nevermind seems the backing is more that just a form, Link

Jayrod's approach sounds reasonable. Maybe a non-starter but they could do selective demo/core drill of the deck over the connection to get a backer bar in place.

 

[azcats]

No way to do a tiny bit of demo there to slide in a backer bar?

 

[DETstru]

Do you need a CJP? Can you check the section with a lesser weld and see if it works?

 

[RPMG]

@ jayrod, I am avoiding flg pl's below because of nearby connections.

@ Celt, I would use the metal deck as backing. I just don't know if that is acceptable. The article states that this is problematic for fatigue at the tension flange, and this is a beam at the compression flange.

@ azcats, I don't if they can demo a tiny piece. They would probably have to core drill like Celt said.

@ DETstru, I can specify B-P8 (J weld with 1/8" land). Does this develop the full flange force since it is always in compression?

 

[kingnero]

Depending on the decking: if it is bare metal (not HDG or otherwise coated, I see no problem doing a CJP weld in that position.
Only thing to watch out for, is to avoid excessive concrete heating on top of the decking.

http://www.fusionpoint.be

http://be.linkedin.com/in/fusionpoint

 

[RPMG]

J1.4(b)(i) basically says that if most of the compression flange is PJP welded with 0 root, it will have full capacity.

Thanks All!

 

[KootK]

This has been a learning experience for me as it never even occurred to me that you could do overhead penetration welding. I guess it's not so different from multiple pass over head fillet welding. I'd be wanting some thorough QC testing though.

I'm not sure that a zero root approach is advisable here, simply for the fact that I'm not sure it's achievable. The root will be involved in the takeup of your length tolerance and, more importantly, angular tolerance for the new beam. It's hard to imagine that you'd manage both the zero root and proper fitup.

It sounds crude but could you bevel the edge of backup plate and just bash it under the deck as a wedge of sorts? You might compromise a deck weld locally which surely isn't a big deal.

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.

 

[RPMG]

We've done overhead groove welds/splicing with this contractor before, and we haven't experienced a QC problem.

B-P8 is prequalified with R = 0. Wouldn't a PJP weld be better for fit-up than a CJP?

And I'm open to bashing in a backing bar. How do I determine the minimum thickness?

 

[KootK]

B-P8 is prequalified with R = 0. Wouldn't a PJP weld be better for fit-up than a CJP?

I speculate not as any rotational tolerance would involve a gap forming at one or more of the welded joints.

And I'm open to bashing in a backing bar. How do I determine the minimum thickness?

There's a table for this in AWS. Depends on your particulars as you can imagine.

I've got an alternate idea but it'll take some sketching. Get your checkbook ready.

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.

 

[KootK]

Nope, I got nothing. I'd thought that the slab terminated short but now I see that it's just got its break-line in a different place.

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]

If attaching to the top flange is absolutely impossible, you could take the moment out through the web. Not the best solution, but it may be possible depending on your loads. Think of it as a WT section that you are trying to splice. I am envisioning a healthy size place on each side of the web.

 

[RPMG]

I spoke with a welder, and he has done both slab cut-outs and overhead PJP's to splice beams. He recommended PJP's for a number of reasons. ASIC Table J2.5/J1.4(b)(i) is very clear that non-column compression connections finished to bear should be designed for a tension force equal to half the compression strength required, so this issue is resolved.

Thanks!