Fastening Cement Board to Structural Steel 2

[bookowski]

I've got a small building where the client wants a structural steel perimeter frame (light w10's) with cold formed joist infill and cement board subfloor, something like structocrete by usg. This is a very low seismic area and the building is small enough that wind demands on the diaphragm are very small (the perimeter beams could almost take the wind in weak axis).

Is it acceptable/typical to use a self drilling screw, something like the Simpson version, to attach the CB to the flanges of the wf sections? I don't see anything addressing this in the CB literature. In my limited experience with CB I've found it quite brittle and prone to edge breaking even with standard fasteners, so I'm wondering if it will hold up to this (if it's even allowed). If this isn't a good idea what would be a reasonable attachment from CB to WF?

 

[Brad805]

It will be quite time consuming to attach the cement board if your flanges are 1/4" or thicker. The head will be a tad unsightly too if anywhere you can see it. I would likely let them shoot a 2"x_ nailer to the WF and let the cladding trade use their standard fasteners. Some may prefer to predrill the beam and use carriage bolts to attach the nailer.

 

[bookowski]

I don't have any depth tolerance for a nailer over the wf beam. Heads could be dealt with, they've got a thick buildup on the floor that could bury these. The only near zero depth equivalent to a nailer would be to have thin plate, maybe ga material, welded to the top flange and overhanging and use standard screws to that. That feels nuts though.

 

[XR250]

Does it have to attach to the red iron? If the loads are low, can you not make the CFMF attachment to the red iron take the in-plane and out-of-plane loads?

 

[bookowski]

@XR - Maybe, but I'm not sure of a non-crap way to do it. In the joist parallel direction I've got 10" deep CF joists (a bit under 19ft span) adjacent to W10's for a perimeter moment frame. I could have a cf angle attached to the underside of the top flange and place the first cf joist tight to this angle, screwing the web of the joist to the angle. Not pretty.

 

[milkshakelake]

I try not to do this; most of my details have nailers. But if there's no option, I specify self-drilling Teks #12 screw (or approved equivalent) @ 6" OC. I don't know how viable that is in the field. But I don't get RFI's about this, so it must be okay that I've specified it. We practice in the same area, I believe. Dragonboard is the common deck here and that is a magnesium board, not a cement board. So it's not really an apples-to-apples comparison. Maybe specify predrilling each hole to cover yourself...though it might be a fantasy that anyone would actually do it and be able to line it up everywhere.

 

[XR250]

maybe just shoot a 12ga plate into the top of the W10 and let it hang over and they can attach to that.
I would put some blocking in that first bay regardless.

 

[dold]

Try PAFs with washers? I've used them to attach plywood to hot rolled steel before when a nailer wasn't possible.

 

[bookowski]

@milkshake - yes, i've also specified it in the past and not heard complaints but I wouldnt be surprised if they just didn't put in 75% of the screws and/or the cb broke apart where they did. I've specified dragonboard but never seen it in person, they ask for the same cb screws. If it's a bit more ductile that'd make me feel better. CB is junk in my experience, it's like screwing through chalk and hoping it doesn't snap.

@XR - Yes, I was thinking of options like this but it seems mess. Maybe better off to specify self drilling because it looks cleaner on paper, they don't get mad until it's too late at least.

@dold - I think pafs, even with a washer, would blow apart cb but just a guess

 

[milkshakelake]

I use PAFs for sheet steel to real steel/concrete or something like that. I'm afraid it would rip up a cement board, and a PAF that's not an X-U or something similar (like the ones for wood sill plates) would be too weak to penetrate a structural steel flange.

 

[Tomfh]

They can batten off the steel, or fasten on a nailer, or a cold formed angle, or similar, and fix to that. We're in "teaching grandma how to such eggs" territory here. Give them a beam to fix to, and they can take it from there.