Welding Rebar

[ataman]

Hi,

A contractor damaged a r/c retaining wall and had to have to wall demolished and repaired. In order to save time he cut the rebard but cut it about 1 foot above the footing and as such the required lap lenghts can no longer be satisfied. I've already checked As provided versus As required.

The contractor has proposed welding using a 6013 electrode which has a yield strength of 410MPa (60,000 psi) but I am a bit weary since where I am located welders don't go through any formal training and certianly they don't practice to AWS. The rebar is 400 MPa steel. From my readings he needs to use an electrode with a yield atleast 550 MPa (80,000 psi) and there are other issues regarding the carbon and Manganese content of the rebar.

I know this may sound weird but is it possible to ask the contractor to provide standard hooks for both the steel that is sticking out the footing and the new steel that is being placed to reduce the development length?

Alternatively I can have him drill and epoxy dowel into the footing.

Any thoughts? Thanks.

 

[JStephen]

We use welded rebar for certain applications, but have to buy a specific grade for it to be weldable. Don't just assume that the rebar in question can be welded.

They make couplings for splicing rebar; could you use them?

 

[HgTX]

What kind of 400 MPa steel? What specification? What chemical composition?

Hg

Eng-Tips policies: faq731-376

 

[msucog]

i agree with jstephen's comments. i also agree with the mechanical coupling question (even if they are pretty expensive).

it make be more cost effective to drill and epoxy new bars in to the footing as long as the designer approved such a fix. drilling and epoxying so many bars at such a critical location in the wall doesn't seem desireable to me but i'm no structural engineer.

 

[EngineerTex]

One of the most interesting courses that I ever took was a week-long class taught by an engineer for Lincoln Electric.

To address something that you wrote, there is never a reason to overmatch a weld. Using a weld material that is of a higher strength than the parent material can never do any good, and often, it can only do harm. If you have rebar with a YS of 400 MPa, you should use something that has a YS of around 400 MPa or less. Overmatching the weld results in an extremely strong weld that will overly stress your rebar during weld cooling. Matching the weld strength to the parent metal strength allows the stress to distribute itself across the two. And just as a further point, the weld electrodes usually have a MUCH tighter control of metallurgy and you can usually guarantee a lot of ductility in the weld material such that if you undermatch the weld strength, the weld can deform without cracking. Plus, any stress you put into the weld has to come through the parent material and welding it doesn't make the parent material any stronger.

Also, if the contractor says that it's an E6013 electrode, make sure that it really is. Often, someone will spec an E60xx electrode. Note that an E6019 electrode has a YS of 48ksi and a min tensile of 60ksi. E60xx electrodes are not interchangeable.

However, the two most important points are these:

1) If you cannot be absolutely certain of the metallurgy of the material, DO NOT WELD.

3) If you do not have a competent, certified welder, trained and experienced in the exact welding procedure for the task at hand, DO NOT WELD.

I know your question was about hooks, but I wanted to say that welding doesn't have to be hard if you're careful.

Since you have a shorter-than-required lap length for a normal splice, can you instead use two pieces of rebar, each with about half of the cross-sectional area of the existing pieces and weld them on each side of the existing piece? Is that just a crazy mech engr talking?

-T

Engineering is not the science behind building things. It is the science behind not building things.

 

[Teguci]

If you provide a hook on 12" of rebar you still don't have enough length to get a hook development length in there. You will still need a hook development length of Ldh = 1200 db / rt(f'c) plus applicable factors.

Go with a mechanical splice: Erico, NMB, etc...

 

[structuresguy]

I would use mechanical couplers on the existing bars. I would not weld them if they are not weldable rebar, which would be unlikely if it was not originally required.

 

[hokie66]

That's a shame. In Australia, our standard reinforcing steel (500 MPa yield) is weldable, in most cases without preheating.