steel weldability 1

[ajk1]

Given the chemical composition of the steel as determined form specimens cut form existing rebar from an old building, how is the weldability determined?
What is the formula, and what is the criteria for assessing its weldability?
Is the formula for wledability as follows:
%C + %Mn/6 + %Ni/20 +%Cr/10
correct, and if so, what is the acceptance criteria? If this is not the correct formula, what is?

A representative specimen is as follows:

Carbon 0.39?
Manganese 0.66%
Chromium 0.04%
Nickel 0.04%

 

[TXStructural]

That formula does not guarantee weldability. Other factors include the degree to which the bar has been stressed and the nature of the grain structure of the steel.
A good, certified welder should be able to weld the material, but welding old rebar frequently requires preheating. The minimum preheat temperature is determined by a slightly different formula (see AWS D1.1 for that formula as it does not yet appear in D1.3.) There is movement at AWS to require preheat determination for all welding, even steels designed to be weldable under usual conditions using prequalified welds.

The CRSI publication "Vintage Steel Reinforcement in Concrete Structures" may help you identify bars and know what to expect.

 

[kingnero]

EN 1011-2 states exactly what you need, it's a european code so it might not be applicable everywhere. The technical background is (should be) the same everywhere, though...

 

[ajk1]

To TXStructural and Kingnero - ok, I will pursue that. Thanks very much

 

[Ron]

Agree with TX. Excellent post.

 

[ajk1]

Attached is my preliminary drawing. Have I said enough regrding the welding, and in particular the preheating? Is there anything more I should day, or give a reference to a Standard (bearing in mind this is in Canada with respect to reference standards).

 

[kingnero]

had a quick look, you only say "preheat" but not how much?
A quick google gives you this as result.
Check in particular annex C
EN ISO 17660 might be interesting too

 

[KootK]

Two comments:

1) I`d weld for 1.25 x As x Fy rather than phi x As x Fy. That seems to be the standard for mechanical couplers, even in non-seismic applications. Logically, you want the stirrups to be able to yield, and perhaps strain harden some, before the splice would give way.

2) I`ve never seen rebar welded on one side only (the new 10M`s). I can`t quite put my finger on why this bothers me, but it does. Could you slip a steel plate in behind the damaged stirrups and weld to that instead?

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.

 

[ajk1]

To Kootk -
- on your point 1): ok
- on your point 2): page 18 of the reference that kingnero sent earlier in this string shows the bars welded one side only, just as I drew in my drawing. I am not sure that I am keen on putting a plate in behind the bars, because to weld properly to the plate means separating the 10M bar from the existing #4 bar sufficiently to get access to make a proper weld of the bars to the plate, and I am doubtful that is a good thing.

Thanks for the comments.

To kingnero -
I find the reference you sent interesting, but on the issue of what temperature to preheat, I find the graphs incomprehensible, although maybe it would be more comprehensible if I spent more time studying them. I think if I cannot find the preheat temperature, then I will just require that the welding inspector approve the preheat temperature. I would have thought that a welder certified to weld rebar would know the proper temperature - no?

Thanks for the information.

 

[KootK]

- on your point 2): page 18 of the reference that kingnero sent earlier in this string shows the bars welded one side only, just as I drew in my drawing.

I see what you mean. Although it's hard to know whether that sketch is a) intentionally sanctioning one sideed welding or b) just saying how pre-heat should be handled. This document suggests that one side lap weld splices are a real thing where eccentricity is not a concern: Link

I am not sure that I am keen on putting a plate in behind the bars, because to weld properly to the plate means separating the 10M bar from the existing #4 bar sufficiently to get access to make a proper weld of the bars to the plate, and I am doubtful that is a good thing.

There's been a misunderstanding here. In my proposed solution, the 10M bars would be deleted. The backing bar would connect the stirrup segments above and below the defect directly.

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.

 

[ajk1]

To Kootk -- ok, now I understand what you are saying, and it seems like a good idea indeed. Thanks very much.