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Fancy Door Bulkhead Attachment to Structural Steel Lintel 4

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Structural
Jan 15, 2021
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I have a long fancy door that weighs roughly 1000lbs (total weight over 23 linear feet) that will be hung from my structural steel lintel (HSS 12"x8"x1/2"). I'm the steel subtrade / delegated designer but as a favor to the GC I am designing the bulkhead attachment for the window contractor since they won't do it. Loads are low but it's a real, real fancy door and the window contractor has been sparse with details. I would rather overkill this thing than have any issues in service. What I'm looking for is help with is the following:

1. What fasteners to use through the 3/4" ply to the structural steel. Drilling is a given due to the thickness of lintel. Need low profile head since I don't want to recess too much as that'll possibly lead to pull-through of the outer 3/4" ply. Anything Hilti is preferred (easy to procure) but PAFs will not work per the window contractor (head sticks out too much)

2. How to handle the two ply problem (i.e. how worried am I about these separating and what measures should be taken to ensure they act together)

3. Anything else I need to know about fancy sliding doors. Peculiarities with fancy stuff is something I don't have too much experience with.

Figure 1: This is from Window contractor's shop drawings. Apparently their standard is 2-plies of 3/4" ply with wood screws through their track. Not sure why a single piece of lumber won't work but they're adamant about the two 3/4 plies. They have no idea about the spacing of their attachments, so I'll probably work backwards to see what the max span is for the 3/4" plies (assuming one fastener per panel - should be conservative - or max capacity of a single wood screw) and state that as max fastener spacing on the drawing.

Capture1_ssusgr.jpg


Figure 2: Kind of what I was envisioning. I put screws as 16" c/c as a placeholder for now but as mentioned above will check max span of a single 3/4" ply. To get the two 3/4" plies to work together was going to wood screw them and use adhesive between the plies. Stagger joints.

Capture2_xk4ljq.jpg
 
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Some thoughts -

We use a ton of Elco (now Dewalt) Dril-Flex and Bi-Flex (stainless) self-drilling / self-tapping screws into steel (and aluminum). Much better than "Tek" screws, as they are manufactured in a way that minimizes hydrogen stress / corrosion issues. They have some undercut flat-head options.

In terms of the screws into plywood, unfortunately I don't believe that there is much out there, short of a technical guide from the APA. And the capacities aren't great.

Personally, I can't say as I like this detail - I wouldn't want to transfer the load through the plywood (which is how I am interpreting it). But can't say as I have faced this type of issue.

FWIW
 
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I despise these door manufacturers. They have incredibly heavy, hung doors that they know have to be supported on steel, but refuse to allow you to fasten their product to the steel.

Biggest issue in the overall design is usually serviceability. Most of them have 1/16" (or similarly insane) total load deflection limits regardless of span.

Looks like there's a layer of gyp in between the plywood and the head, which isn't great...but should negate the issue with heads? Drill out the gyp at the fastener locations and you're good.

Hilti PFH screws may work for you. They're meant to be self drilling, but I agree you should pre-drill for a 1/2" tube.
 
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jjl317: Thanks for the screw suggestion. The tables look great and I will definitely give these a go. You are correct in that the plywood is affixed to my steel, and the door is hung from the plywood. I dislike it too (why not screw straight into the steel?) but I'm just a steel guy trying to help out my client. Door guy said this is how it is so I am trying to make it work mostly so that the plywood doesn't fall off. If the door falls but the plywood holds, then I'm all set.

phamENG: These guys are awful. "What is the spacing of your fasteners along the plane of the door?" Is met with "See shop drawings" which show absolutely none of this (or fastener type or diameter or load per fastener...). Though by the sounds of it this crew is slightly more reasonable than what you are used to. They gave me a generous L/360 or 1/8" max for the door load only. If they wanted total load I would have told them I can't do it given the spans (I actually have 3 of these things all slightly different. Bulkhead condition is same though).

Great point about the drywall. They told me PAFs wouldn't work because of the heads so I just ran with that without thinking. Would you be willing to comment on fixing the plywood plies together? This is the part I am most nervous about. I don't want them to screw into these things, have them separate (because not fully adhered or whatever) get half the pull-out value they're "expecting".
 
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I think you're on the right track (sorry...).

The controlling failure mode will likely be pullover of the plywood. Here's a paper from AWC's website that conveniently looks at a 1-1/2" thick section of two glue-laminated pieces of 3/4" plywood evaluated for pullover of flat head wood screws. I haven't read it, but it seems like it may be helpful.

The only reason for the intermediate, 1.5" screws would be for shear to ensure they act as one to resist out of plane loads. No doubt you'll need that. But they won't help with the tension if you have the main screws sized to prevent both pullout and pullover.
 
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With 1/2" steel, you still may be snapping screws even with pre-drilling. Be prepared for that.
 
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XR250: Interesting I had not considered this. Actually after looking at the Elco Dril-Flex it looks like they max out at 5/16" base steel. And the Hilti PH WD tap out even less. So I'm still looking for a fastener (perhaps Hilti S-MD 12-24x3 HWH #5 Kwik-Cote seems to go up to 1/2" base material).

Given what phamENG said about drywall covering the heads, perhaps I tell them that PAF is the only practical way. My concern there would be firing through two sheets of plywood. If the first sheet isn't in full contact then some of the energy of the shot may be absorbed by the plywood movement and penetration into base material is then not sufficient.

It really does seem like a 2x with PAFs directly to the steel would solve some issues here. We have the drywall to cover the heads per phamEng, so should be no clearance issues. Can anyone think of a reason why going 2x instead of two 3/4" plies screwed/glued would be a bad idea?
 
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Enable said:
XR250: Interesting I had not considered this. Actually after looking at the Elco Dril-Flex it looks like they max out at 5/16" base steel. And the Hilti PH WD tap out even less. So I'm still looking for a fastener (perhaps Hilti S-MD 12-24x3 HWH #5 Kwik-Cote seems to go up to 1/2" base material).
Click to expand...
Paf's may not penetrate enough to pull the 2x tight.
I have used Tek5's that were rated for 1/2". I used them in 3/8" steel and probably broke 20% of them.
 
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For what it's worth, both the Dril-Flex and Bi-Flex documentation says the #5 tips will drill up to 1/2" thickness steel (though as a desk jockey, can't say as I have ever personally installed them in 1/2" material).

 
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Based on the shop drawing detail, I find it hard to believe the weight of the door is suspended. The fasteners could be for lateral support, but I’m guessing the weight is supported at the floor. There just ain’t no way wood screws into strips of plywood are supporting a 1,000 lb door.
 
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Loads are low so idk if this'll effect much but did want to flag that you probably won't get 1000 lbs distributed along the full length of the system. When the door is in the open condition, you'll have the three lites occupying the length of one piece of glass (assuming its equal length glass) with what appears to be pretty flexible framing. I'd want to consider that more concentrated load at any locations where the sliders are able to stack up in the open condition.
 
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You could pre-drill the 1/2" steel so the self tapping fasteners don't have to work as hard. Most of them have some guidance on this.
 
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Thanks everyone for their help.

In what amounts to a somewhat wonderful conclusion to this affair the GC decided to go on their own and install a random number of self-drilling / tapping screws into two layers of unbonded plywood. I did notice that they snapped about a third of the fasteners even with pre-drilling as XR250 suggested. But they did get it done. So now we know it's possible!

After pondering this a bit I think I would have gone with one of the following options should the detail arise again:
1 - Fusion Welding studs with nut into drywall and excess rod grinded off. Glue and screw between plywood layers.
2 - Rivnuts with same idea as (1) for rod + nuts
3 - Shit ton of self-drilling / tapping screws to account for loss + glue & screw plys together

phamENG: I had originally given some thought to dimensional stability but dismissed it because the environmental conditions are static. These doors are separating interior spaces kept at the same temperature and RH (+/-). Though your prompt did lead me to think about other 1.5" engineered lumber that might work. It led me to something called LVL-C, which apparently is an LVL with laminations in both orientations to help with cross grain bending applications (European handbook here). Though my suppliers didnt have access to it here so maybe it's a Europe only thing for now.

bones206: I would have thought so as well but these are sliding without a bottom track as far as I know. So they must actually be top hung. Pretty wild though.

RenHen: This is a good point and I did consider that when designing the lintel. I used 1000lbs mid span for deflection calcs. Though realistically the sliders will congregate at the sides so for blocking purposes that's where there should be closer fastener spacing for sure.
 
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Are these doors glass? The 1000# seems pretty low to me for a 23' span.
 
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Door shops give assembly weights and that's what they provide so I ran with it. Seems reasonable though since this is a single pane system as it's dividing two interior spaces. Glass is 3/8" thick and the door is 9' high. So a quick calc gives 9' x 23' x 4.78 lbs / ft2 ~ 1000lbs give or take. I'm sure the aluminum adds some but not much.

Maybe you're thinking of double pane assemblies for separating exterior / interior environments? Anyways I never actually double checked the weights they gave so thanks for reminding me that I should be better at that!
 
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