Stud welding on 20ga over 1/4in angle

[Mixtli]

Hello there,
We are planning to weld some 3/8in stainless steel (SS) Nelson studs onto our trusses, chords made of 2L2x1.5x0.25in; we want to use galvanized sheet metal as stay in place forming for our concrete on top.
The reason to use galvanized sheet metal is for corrosion protection. The sheet metal is only for pouring purposes, I don't want to design as composite cause I don't have enough bonding between metal and concrete, and other reasons.
Any comments on how this could be done achieving full corrosion protection?
Could I by any chance use just black sheet metal and let it rust with time? it is not structural. Would the rust stain the concrete above and surface with time?

We are thinking on coating the trusses with either primer or galvanizing: Will this interact negatively with the stud welding process, or maybe I should use a special procedure (clean surface, etc)? but, having the sheet metal in between stud and truss complicates things, like touch up, no? any ideas?

Never done this before for an exposed to the elements condition, so any help will be really appreciated.

Mixtli

 

[jayrod12]

Most of the time in my experience the studs are welded on first, then the entire assembly would be primed. What kind of environment will this be in that you feel the need for corrosion protection.

 

[dik]

The 20 ga may be a little thick... matter of checking and check condition at laps. The 3/8 dia should be checked against the minimum base metal thickness, but should be OK. Why stainless steel if enclosed in concrete? Corrosion issues? may have problems where HDG is burned off deck. Check with a local fabricator to see if any issues but it should be doable.

Generally don't prime composite shear connectors, and are you looking at the concrete being continuous over the joists? Are your joists primed? often don't for interior work. If they are, do not prime top of angles.

Dik

 

[jayrod12]

I didn't even pick up on the stainless steel aspect of the studs. Be sure you can even do this, in my experience not many people are certified to weld stainless steel to plain carbon steel. It may make more sense to just hot-dip all of it.

 

[dik]

jayrod... it's not uncommon to weld studs through deck to OWSJ. You do not want HDG on the OWSJ for stud welding... interferes with the welding and fumes can be harmful to the welder.

With CSA S16 (Clause 17), the stud dia cannot exceed 2.5* the thickness of the angle and can pass through 2 layers of 20ga material (just checked). There are some other requirements. Other codes may be different.

Dik

 

[jayrod12]

I agree with you Dik. However I feel like if corrosion protection is required then you should be installing the studs ahead of time and HDG the entire assembly. Then install the deck with screws or PAF to avoid the welding aspect.

And I still am unsure whether you can install stainless studs to carbon steel using the typical methods.

 

[dik]

and you have to punch the deck to apply it over the headed studs... if you want composite action. I suspected the use of stainless steel headed studs was because of corrosion and maybe an improper method of dealing with it. If real corrosion then maybe forgo the use of composite action and use PAF (Hilti or something of that ilk) with a special coating on the OWSJ's.

Dik

 

[Mixtli]

Hi all,
well, it is an aggresive environment since it is on the shore line of Lake Ontario. The metal deck will only used as stay in place form, so no composite action, but it is HDG because of corrosion, don't want the rust to stain the concrete long term. Actually the concrete rebar is GFRP.
The studs are there because we want to fix the concrete to the joists, and we are restricted by cover, and so therefore the need for SS, although I am worried the low cover will allow for concrete consolidation around these studs and the formation of cracks.
We were told by the stud vendor that the galvanizing on the sheet metal is in the way of obtaining decent results (he made some tests) so we may be changing procedure.......

Cheers

M.

 

[dik]

Hilti has PAF shear connectors that will not interfere with the HDG of the deck in the vicinity of the stud weld. I don't know what the lengths are. This also allows the OWSJ to be HDG'd.

Dik