Metal Roof Deck Connection to Metal Trusses? 3

[Revv]

Hey Guys,

So I was just wondering how you guys normally connect your metal deck to metal trusses? Why do you use the connections you do? I use the Hilti DF Designer program and it just throws out something and gives me alot of options. I can make several work so are some more economical/Easy to install? Can you puddle weld a deck to metal trusses?

Thank you!

 

[phamENG]

Haven't done one in a while, but I used to spec TEK screws for metal deck to light gauge trusses. An arc spot/puddle weld will just melt right through the light gauge underneath if the welder isn't really careful. I've never seen them done - maybe somebody else has.

What options is it giving you? (I've never used it, but I see it's free, so I just downloaded it. I'll try it out on my next steel deck project.)

 

[KootK]

Spot welds have been very popular up here for a long time. They can certainly be done with weld washers etc but it requires the welder to have a specific qualification for welding deck. And finding folks with that has been tough at times.

Most of my decks these day go out with Hilti pins specified as the fasteners. I deal with a lot of substitution requests on this but I've come to view that as just part of the exercise. Interestingly, the seismic ductility of the pins tests out much better than welds. They kind of slide around in their holes, bending metal about as they go.

 

[human909]

It is pretty much all tek screws or even kliplock into preplace clips on the cold rolled purlins on this side on the hemisphere. In cyclonic regions it is closer spacing of tek screws.

KootK what are the conditions there that make welding worthwhile?

 

[dik]

I nearly always use TEKS for CFS material. It's generally too thin to get a positive 'puddle' weld.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Do you feel any better?

-Dik

 

[KootK]

KootK what are the conditions there that make welding worthwhile?

1) Mostly just habit and inertia.

2) We're a very industrial area owing to our oil production industry. As you probably know, industrial folks tend to not bat an eye at some of things that would be concerning cost issues on commercial and residential projects.

3) I've been involved in a couple of AESS projects where there was concern for fasteners projecting below the framing and looking yucky.

When I got started in the Midwest US in 2000, I believe that it was still the default to specify welding. The pins and screws were viewed as the "new fangled technology" alternative. There were a lot of substitution requests to go to pins and screws and we routinely received visits from the fastener suppliers to educate us on the benefits and code acceptability of those products.

For anyone who might be curious about it, this is a pretty good primer on how to properly weld deck: Link

 

[phamENG]

Probably worth taking a step back and verifying what the OP means by "metal trusses." When I talk about metal or steel trusses, I'm talking about the light gauge equivalent to MPC wood trusses. Not something that takes spot welds easily even with a washer (which usually go on top of the deck to preserve the deck if it's too thin). If we're talking about open web steel joists with rolled shapes for chords and either round stock or rolled shapes for webs, then I agree that welding is the way to go.

None of the use cases KootK is bringing up sound like they are applicable to the very utilitarian (ugly) and generally light duty light gauge trusses I'm talking about, so I don't think we're talking about the same thing.

 

[KootK]

Yup, I've been assuming "metal trusses" to mean joists fabricated from hot rolled steel. "Metal" is an unfortunately imprecise term.

 

[KootK]

I suppose that CFM = Cold Formed Metal.

 

[XR250]

I have heard stories from field guys saying that PAF's do not work well on smaller bar joists as the flange deflects and they "bounce off". Not sure there is any truth to that but would be nice to hear other's experiences.

 

[hokie66]

A lot of imprecision here. 'Metal' is one, and 'deck' is another. Is this steel deck or steel roofing that is being connected to something?

 

[JLNJ]

Our local Hilti guy said there is a severe shortage of the pins and some big jobs had to go back to welding.

Supply Chain Issues!

 

[driftLimiter]

Verco has a design guide [URL unfurl="true"]https://vercodeck.com/wp-content/uploads/2021/04/Roof_Deck_Design_Guide_V2021.pdf[/url] Which goes through the pros/cons of different fastening methods. The fastener selected may have an impact on the strength of the metal deck when used as a diaphragm. We use a combination of PDF's and puddle welds typically for metal deck diaphragms. Also important to note, that some fasteners have limitations on the thickness of the connected metal.

 

[Enable]

I have heard stories from field guys saying that PAF's do not work well on smaller bar joists as the flange deflects and they "bounce off". Not sure there is any truth to that but would be nice to hear other's experiences.

That happens but can be mitigated somewhat by A) using lesser charges and B) dialing back the setting on the applicator. The more annoying thing is that if you dial things down it will work well for some but not drive enough for others. The variability can be a real struggle; do expect some pins to completely blow through the flange on smaller sized members.

Overall though I'd still 100% recommend over welding. Here's me a couple years back looking like I'm about to miss a joist flange. They were very thin joists (20' span only moderate snow load) and the bounce was there but not enough to get in a fuss over. I'd wager the field guys you talked to are just used to finding a particular setting and not adjusting for the various material thicknesses.

Also important to note, that some fasteners have limitations on the thickness of the connected metal.

Definitely. Hilti produces a couple we use for different base material thicknesses. We use the X-ENP for things > 1/4" and the X-HSN 24 for around 1/8" to 1/4"

 

[NorthCivil]

I remember heading a lecture in post grad about the testing of metal roof decks puddle welded down for seismic, basically the whole deck just unzipped with minimal stress.

The uni held a special lecture for local engineering companies to show them the results, the audience all were sitting there chewing their nails as puddle welding the decks down was the go to local practice. apparently that changed quickly.

 

[driftLimiter]

there is nothing wrong with puddle welds or arc seam welds for the connections. There are test that show pretty good seismic performance using them. One of the issues is reliability because it can be pretty easy to burn out the deck all the way and compromise the connection.

 

[CrabbyT]

For a 1.5B roof deck, I usually spec 5/8 puddle welds in a 36/4 pattern (12" o.c.)

 

[haynewp]

I use all screws for type B deck to CFM trusses. I also agree with the fasteners performing better under seismic than welds.

 

[RangeRock]

Vulcraft also offers a relatively robust deck diaphragm design tool using the 2018 IBC data and a variety of different attachment methods.

Pretty slick for quickly determining required weld/attachment patterns for diaphragm loads.

https://vulcraft.com/DesignTools/IBCDeckDiaphragm2018