Electrical resistance welding on structural wwm

[Mixtli]

Hi all, not sure if this is the right forum, but here it goes:

The cross joint of structural mesh shows one wire embedding into the transverse one which is the result of the electrical resistance welding, right?
I'm just wondering if there should be any concern on the reduced cross section due to this fusion. The steel on one direction will work as flexural reinforcement on tension and compression sides, and the steel in the other direction will work as temperature reinforcement.

I attached a picture for clarity.

Regards

 

[tbuelna]

Looks like a re-bar structure based on the picture. Don't recall seeing many concrete re-bar structures constructed using resistance welding. Typically these connections are made using stick or MIG weld, or wire wrap. The re-bar used in concrete structures is designed to take tension loads, so the reduced cross section at this undercut is probably not helpful.

 

[Duwe6]

Tentatively concur with tbulena. Looks 'hinkey'

Suggest that you gather up some of the 'drop' from the construction and figure a way to pull one joint apart. Aside from being the traditional method of testing ERW welds, it will show you the amount of fusion - look for crystalline [intergranular cracking] and shiny [transgranular tearing] spots. Just like checking spotwelds on sheetmetal. If it looks like there is a significant amount of 'wasted' area; black slaggy junk, neither good basemetal nor good weld [crystals or shiny], it is time to 'challenge' the material and have calibrated tensile pulls made of it. Those tensiles should meet or exceed the minimum spec for plain rebar of that grade & diameter.

 

[dhengr]

Mixtli:
There will likely be some notch affect at each weld joint, HAZ, actual mechanical/geometric notch caused by, lack of fusion, weld defects, etc. How much is hard to tell. If you have good fusion btwn. the two rebars at the weld joint, you probably haven’t lost much in the way of bar dia. or area; you’ve just fused the two bar together and you are stressing the material in a biaxial fashion at each of the joints, as opposed to a strictly axial way that we normally assume for rebar. I assume this matt welding is being done in a shop, under controlled conditions, and is primarily being done to facilitate handling of the large matts of rebar in transit and on the job site. I would talk with the rebar fabricator about any weld testing that they have done, and do some testing of your own, as suggested above by Duwe6. I would do two types of testing: first to check for weld quality and good fusion so you have some confidence that they are not inducing an actual large mechanical notch in the rebars; and secondly some tension tests, in both directions and on many samples, to assure that the rebars are measuring up to their req’rd. tensile cap’y. Check with ACI and CRSI, or like groups up in Canada, on this practice.