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Field Welding Non-Weldable Rebar 2

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KootK

KootK

Structural
Oct 16, 2001
17,990
4
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CA
Context

- Grade beam on a local infrastructure project. It supports a fence that keeps sabre toothed tigers from eating babies. Low importance factor as with most livestock stuff.

- An unfortunate core has been made through the grade beam top reinforcing.

- Various constraints are making it desirable to get this repair done in as localized a manner a possible. The fence is already in place and its anchorages are nearby to the location where this repair will take place. The repair location is also very close to a plan "corner" where the grade beam changes direction over the pile.

- Quality control on this project is good. You know, other than this ridiculous core.

- One repair option being considered is field welded splices of the reinforcement. This is not weldable rebar, however, so we'd have to deal with preheat.

Questions

How good -- or bad -- of an idea is it to consider field welded reinforcement splices here from a QC perspective?

Is there any danger that the preheated bars would expand and cause the cover concrete of the grade beam to spall?

01_cifoau.png


c02_p1jdan.png
 
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KootK said:
How good -- or bad -- of an idea is it to consider field welded reinforcement splices here from a QC perspective?
Click to expand...

Not sure I have enough knowledge to share about it from a QC perspective, but I think it opens you up to a ton of scrutiny from anyone that wants to provide it. I would probably be looking at using a mechanical splicer and re-pouring the grade beam back with a non-shrink, high-strength, corrosion resistant grout product.

KootK said:
Is there any danger that the preheated bars would expand and cause the cover concrete of the grade beam to spall?
Click to expand...

I've had cracks in concrete elements from welding to embedded plates with nelson studs. It depends on the amount of heat that gets placed into the rebar - but that becomes reliant on the person doing the welding.
 
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How far back are you going to remove/chip away the concrete to make the repair? 1" away from weld (and preheat area) I could see it possibly (probably?) being an issue. 1ft away from weld, probably much less of an issue. If you go far enough that you have sufficient room to wrap the rebar in water soaked rags between the weld and concrete that would give you even more protection.
 
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@JAE/Bookowski,

I'd certainly entertain / prefer bar couplers, as would the contractor I'm sure. I do have some concerns however:

1) Because this is a bar gap rather than a bar splice, per se, will I not need two couplers in close proximity for each "spliced" bar?

2) If each bar splice requires two couplers, how much of a gap between bars do I need to create in order to feed the middle piece in there somehow?

3) We would not be able to maintain specified cover to the mechanical splices. Is that something that ca be relaxed locally?



 
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KootK,
My guess/intuition tells me:
1) yes
2) 1"
3) Galvanized couplers?

1) and 3) suggest to me cutting away more concrete each way to expose the required length of existing bar, adding a center splice bar with two couplers for each bar line, then replacing the lost concrete around the bars and perhaps adding concrete above? (don't know if that is possible with your situation).



 
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dauwerda said:
How far back are you going to remove/chip away the concrete to make the repair?
Click to expand...

Thanks for that. I was just about to summon you to this thread.

Tentative chip dimensions are shown in the sketch that I posted originally. There's space for more, just not a ton more. Corner condition sits on a pile with a rather important torsion connection to the beam. I'd not be to excited to have to mess with that.

c01_wbvsfc.png
 
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JAE said:
2) 1"
Click to expand...

That can't be right. I must have explained my question poorly. Try the sketch below.

JAE said:
3) Galvanized couplers?
Click to expand...

Sure. Devil's advocate:

a) Is it just up to my judgment whether or not that adequately addresses the corrosion issues that would have originally been addressed via cover?

b) Is there some minimum thickness of concrete to cast over top of the couplers for that concrete to be "survivable".

c01_mrqh17.png
 
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Is it just top bars?

Can you just say screw it with regards to the rebar, grout it all closed and then bolt some plates to the top or side?

Alternately, is that bottom fence member an HSS rectangle? Is it honky enough that you can run some bolts through it a handful of times and use it to bridge the gap? That might be a bit aggressive if there's glazing and the resultant deflection issues, but you don't need to get the forces far, so it might still get you there.
 
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On the welding idea- part of the issue is you need to have the weld procedures qualified, but if the bar is "unweldable", how you accomplish that may be a problem.
 
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What would be awesome is if there were a two piece mechanical coupler that could accommodate the gap. A lot to ask, I know.

c01_fqy3si.png
 
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TLHS said:
Is it just top bars?
Click to expand...

Correct.

TLHS said:
Can you just say screw it with regards to the rebar, grout it all closed and then bolt some plates to the top or side?
Click to expand...

It's a torsion demand situation so I kind of need most of the perimeter bars. I'm probably could manage some plate voodoo but sorting out the mechanics of that would probably take me until Thanksgiving and it would be pretty ugly for a public space situation.
 
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JStephen said:
On the welding idea- part of the issue is you need to have the weld procedures qualified, but if the bar is "unweldable", how you accomplish that may be a problem.
Click to expand...

Agreed. This has to be possible though, right? AWS D1.4 and the PCI manual both discuss this being done, ideally in a plant environment of course.

I plan to delegate to details of the weld procedure to someone more adroit at those kinds of tasks.
 
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If the torsion loads are moderate, then there's potentially something like this. Likely isn't feasible because of the visibility issues if it's plates and/or issues with glazing in the fence if it's the fence member, but the math would be pretty easy.

Screenshot_2023-09-01_113731_hi89mn.png
 
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Do you have the mill certs for the bar? Do you have field review photos of the bar?

With the former, maybe you're lucky on composition. With the latter, I've had more and more installs where I get 400W for free because it's what's sitting around. This is a western canada thing, potentially, though, because of the seismic benefits of 400W. You might get lucky and see a W tag on the bars in the photos.
 
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Maybe the thing to do is just chip out between the posts and make do with whatever double lap that affords me. I don't supper love my anchorage frustums cutting through the repair but perhaps I just need to reconcile myself to that. I often tell other folks here that's okay.

c01_aqsrlr.png
 
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THLS said:
Do you have the mill certs for the bar?
Click to expand...

No, but I'll get them if we decide to go the welded route. That's a good point about potentially having gotten weldable for free.

THLS said:
Do you have field review photos of the bar?
Click to expand...

Not beyond what I've posted really. What do you hope to see that would inform your recommendation?
 
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Take a close read of W186. The scope of G30.18 says that all bars are weldable given the right conditions.

Screenshot_2023-09-01_114421_x1flyr.png


The 2021 version is a little less fully supportive in its stance, but still just says that 400W is 'more suitable' for welding

edit: The field review photos might show the 400W tag rather than 400 or 400R, which would make life really easy. It's a low percentage chance, but it's free if it's there so if you can check reasonably easily then it's worth doing. If you can get the mill certs then you're already covered though.
 
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If the torsion loads are moderate, then there's potentially something like this.
Click to expand...

You're solidly in the running for the polka dot jersey and the "most exotic solution" award.

My primary concern with that would be stiffness compatibility. I feel as though the grade beam would be in shambles by the time that you properly mobilized that HSS rail in warping torsion.

c01_hwrkkx.png
 
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