Welding Rebar - Bar to bar and Bar to plate

[RFreund]

From past threads:
thread507-55969
Rebar "Weldability"
Another good source of info is the PCI design handbook 6th edition chapter 6

It sounds like A615 rebar can be welded either lapping the bars or welded to a plate. The PCI handbook gives some design strengths and effective throat thicknesses however you would still need to qualify a welding procedure per D1.4 correct?
The procedure would require destructive testing and the person doing the welding would need to be qualified for this procedure, correct?
Are there any example procedures for this?
Has anyone done this?

Not to distract from the above questions (this next question should probably be a different thread but I'll proceed anyway). The contractor is requesting to lap and weld bars as the cast bars are not projected long enough to develop the lap splice. Is there a better alternative? I suppose mechanical couplers?






EIT

http://www.HowToEngineer.com

 

[TehMightyEngineer]

I've never found a place where I couldn't use mechanical couplers as an alternative. I'd use those over welding A615 for sure.

Maine Professional and Structural Engineer
American Concrete Industries

http://www.americanconcrete.com

 

[hokie66]

A problem with couplers is that they sometimes protrude into the cover concrete. In that case, I have used welding with success. As long as the correct procedures are used, by qualified welders, it is acceptable practice.

 

[RFreund]

As long as the correct procedures are used, by qualified welders, it is acceptable practice

This is where I'm looking for more information. If I understand correctly there is a certain amount of preheat required. What are the qualifications of the welder? Is there a prequalified weld? Is there a "common" welding procedure used? In the PCI design handbook, they give equations for strength but they don't really say what welding procedure they are related to. I would think these would go 'hand-in-hand' at least to some extent. Or maybe I don't understand where the line is drawn - can I specify at flare bevel weld with 'x' effective throat for 'x' distance with Exx electrode and it is the contractor's responsibility to submit a welding procedure capable of producing the expected strengths? Even if that were the case I'd still be interested in the procedure.

Thanks again!

EIT

http://www.HowToEngineer.com

 

[bridgebuster]

Take a look at the NYSDOT Steel Construction Manual 3rd Edition, Section 7 Part D. It should have the information you require.

 

[sandman21]

Link

The contractor will be required to submit procedures for welding of the bar. They will need to take some of the bar and have it tested and determine the CE. From that they can determine the preheat and interpass based on Table 5.2 AWS D1.4, you should read section 5.2. The issue with welding A615 is the high temps and usually the close proximity to the concrete. Before A706 they would use bond break materiel to relieve some of the thermal stress on the concrete or CMU.

 

[RFreund]

@Sandman - Thanks for the info.

So it is possible that the contractor has a procedure for which they have already had qualified via testing?
I guess that is my hang up, does the procedure require qualification via testing or no, not for every case?

EIT

http://www.HowToEngineer.com

 

[sandman21]

It is possible that the contractor has a WPS for the type of bar with the welder, if not they will need to provide a WPS, see section 6 AWS D1.4.

 

[MrHershey]

Technically all rebar welds need a WPS. There are no prequalified joints like there are for D1.1.

Agree with sandman that shops and contractors who do this frequently likely already have the WPSs as well as welders qualified to do the work. May even have them for A615.

Disagree with sandman about the 'high heat' and potential temperature damage to concrete. Minimum preheat for most bars really isn't very high as long as you have mill reports and can actually calculate out a CE or have one provided in the mill report. If you get lucky and your CE is below 0.55 like A706 is required to be, you likely won't even need to preheat as long as ambient temperature is above 50 degrees F. I don't see very many A615 mill reports with CEs over 0.65. At that level, you're looking at 100 F preheat up to #6 bars and 200 F preheat for #7 to #11 bars. Really not that high. If the contractor does any field bending of rebar, they technically should be heating bars to 1100-1200 F before and during bending per ACI 301 (#3 to #5 bars may be cold bent once, but require preheating after). ACI 301 also limits rebar temperature at concrete interface to 500 F or below during preheating for field bending, would have to heat a lot more than typically required by AWS to get up to that. And that's assuming your weld is right at face of concrete.