What metal deck connections do you use for K joist? 2

[reverbz]

Hey Guys,

What typical metal deck connections do you use for K-joist? I haven't worked with these before.

also bonus question if you're feeling generous: How do you detail mechanical openings? Angles to girder joists? How do you fasten them?

Thank you!

 

[brucesilver]

Hey Guys,

What typical metal deck connections do you use for K-joist? I haven't worked with these before.

also bonus question if you're feeling generous: How do you detail mechanical openings? Angles to girder joists? How do you fasten them?

Thank you!

Hey! For K-joists, I usually see metal deck just puddle welded to the top chord sometimes with side-lap screws between sheets too.

For mechanical openings, yeah angles to girder joists is a common route. I’ll usually frame out the opening with angles or channel, welded or bolted to the joists. Fastening depends on the load and size — welds, screws, or even clip angles work depending on what’s needed.

Hope that helps!

 

[phamENG]

It's somewhat regional. Around here, arc spot welds are popular (also called 'puddle welds'), but some places use PAFs or even screws if the loads work.

For the openings, yes - angles are normal. They're usually field welded. The joists are usually field welded, so you're not adding anything special by calling for those to be welded. Just remember that you not only need them to support the deck edge, but also to drag diaphragm loads around the opening. Make sure you look at the SDI design guides for deck and diaphragms.

 

[DaveAtkins]

I used to specify puddle welds, but now I always specify screws. Seem a little more foolproof to me.

 

[XR250]

I would not use PAF's in thinner chord joists.
This is what happens and apparently it is a concern...

 

[TRAK.Structural]

I've always used screws. Welds are fine for the joists, but I get concerned about burning through 20 ga metal deck. If using 18 ga or thicker than screws or welds makes no difference for me.

 

[XR250]

but I get concerned about burning through 20 ga metal deck

22ga deck is puddled welded frequently. By definition, you have to burn thru it.

 

[RWW0002]

I would not use PAF's in thinner chord joists.

Puddle welds on thinner chords can also be a big problem. Burn-through of chords is common with inexperienced welders (I have seen them burn a little 10k joist chord angle almost all the way in half before) and can be difficult to repair.

With any attachment method - make sure the fasteners are approved for the material thickness being attached to and make sure someone in the field is paying attention. Sometime this can be a challenge due to the varying (and sometimes unknown) chord member thickness at joists.

I spec welds with the option to use (approved) alternate deck fasteners of equivalent strength and stiffness. Welds are nice in the drawings since they have a fairly established allowable load and stiffness values for analyzing substitutions. about 75% of the time now I see a substitution come through in submittals.

 

[RWW0002]

22ga deck is puddled welded frequently. By definition, you have to burn thru it.

I agree.

Even down to 26 ga. deck is often welded( for floor deck) although weld washers need to be used if <22 ga.

 

[XR250]

Geez, sounds like you really can't win. Burn thru the chord or bend them on smaller ones, Tek screws take a long time on the thicker ones,

 

[TRAK.Structural]

22ga deck is puddled welded frequently. By definition, you have to burn thru it.

Yes, I guess my choice of words was wrong there. Generally I just mean that with thin metal and wide variety of construction quality I prefer screws. Welders can sometimes make a mess out of the simplest things......

 

[RWW0002]

Geez, sounds like you really can't win. Burn thru the chord or bend them on smaller ones, Tek screws take a long time on the thicker ones,

Yep.
Pins and screws have come a long way in the past few years, but still aren't perfect.
Welds are only as perfect as your welder..

Giving the contractor some leeway on method is nice so that if/when something gets messed up you can say - "you had a choice in the matter and you chose X - now lets make sure it is done correctly or fixed afterwards.."

 

[ANE91]

Team PDFs here. I’m skeptical that they can meaningfully reduce buckling strength of top chords. Not to say it couldn’t happen — I just feel like we would’ve seen more issues, given how many Amazons in CA are built this way. Of course, most probably weren’t K joists, but some were. I don’t fully recall. Definitely open to learning more about this. Thanks for the info, @XR250. Good question for the Hilti rep…

 

[driftLimiter]

I stopped asking contractors what they prefer because they always will just say PDF/Screws because its cheaper. I tend to trust puddle welds the most, but after reading some of this will think twice about it on small joists.

How do you detail mechanical openings? Angles to girder joists? How do you fasten them?

Generally with a system of angles that frame to adjacent joists. There is a product called, Quickframe or something along those lines that is a pre-fab and adjustable version of the angle support scheme that many use.

Giving the contractor some leeway on method is nice so that if/when something gets messed up you can say - "you had a choice in the matter and you chose X - now lets make sure it is done correctly or fixed afterwards.."

In principle I think this is a great strategy. But just be careful because the fasteners selected may have undue affect on the diaphragm strength and stiffness. If we give them options consider the worst case I suppose and make sure they both work.

 

[RWW0002]

In principle I think this is a great strategy. But just be careful because the fasteners selected may have undue affect on the diaphragm strength and stiffness. If we give them options consider the worst case I suppose and make sure they both work.

See note in previous post. I spec welded with a defined pattern(s) and allow substitution for submitted and approved alternate attachment of equivalent strength and stiffness. So far so good, but I do not allow this option for projects where diaphragm strength or stiffness is especially critical.

 

[JAE]

There have been projects where I walk in under a completed deck and see stars of light everywhere....i.e. burn-through welds.

That said we also typically spec welds/screws/PDF's as options - ensuring that the required diaphragm stiffness and strength is equivalent.

 

[Flotsam7018]

I started out as a welder/fabricator - puddle welding deck was one of my least favorite jobs and yes, burning through is extremely common. It's honestly more difficult to perform correctly than a SMAW AWS D1.1 unlimited test I would say, and you have to do it hundreds of times in a row, usually on your knees, breathing in the galv fumes. It's just a crude tool for the task. I always prefer screws/PDFs.

 

[RWW0002]

I take it from several responses that "PDF" (I am assuming "Power Driven Fasteners") is the new term for pins then.. From Powder Actuated Fasteners (PAF) to Power Actuated Fasteners (PAF) to Power Driven Fasteners (PDF)..

This is almost as bad as welded wire reinf. a few years ago (Wire Mesh to Welded Wire Fabric (WWF) to Welded Wire Reinforcement (WWR) to... who knows whats next)

Hard to keep up these days.

 

[ANE91]

I take it from several responses that "PDF" (I am assuming "Power Driven Fasteners") is the new term for pins then.. From Powder Actuated Fasteners (PAF) to Power Actuated Fasteners (PAF) to Power Driven Fasteners (PDF)..

Yes. Blame Hilti. They make battery-actuated fasteners, gas-actuated fasteners, and powder-actuated fasteners. “Power driven” is my go-to umbrella term. Apparently they now make a cool mobile/handheld stud-welding tool. Not sure what that’s called…

 

[RWW0002]

I's sticking with PAF's until someone complains or PDF's becomes so common I am forced to change. PDF is already taken in my vernacular (.pdf files.) I only have room for so many abbreviations in my memory bank these days.