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Slip critical connection parallel to slot with filler material

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canadiancastor

canadiancastor

Structural
Apr 13, 2014
34
CA
I have a light weight box structure meant to be hung on the exterior of a building on cantilevered channels. As it is outside of the building envelope, it would be exposed to rain, which is why I'm thinking of having it hot-dip galvanized. To keep things adjustable, I'm being asked to have horizontal slotted joints in both directions (for X and Z direction adjustability) with the use of filler material (for Y adjustability). I'm not sure whether this is reasonable or not because the loads are pretty low (in the order of 2 kips in shear and 2 kips in tension). I would be using slip critical connections, and calculating with AISC-360-16 J.3.8 leads to something around 4.8 kips for each 2 bolt connection (1 filler between connected parts, 1 plane needed to slip, Class A surface for hot-dip galvanized).

PP_20210603_071212_uw0xpi.png


Second question, for the filler material, I'm being asked whether we could consider something like Koralath instead of galvanized steel plates. I don't see any issue with regards to durability, but I haven't found any information with regards to the coefficient of friction of Koralath. I also recall seeing somewhere that filler material needs to be non-compressible in slip-critical connections, I don't know if anyone has a more specific definition of "non-compressible".
 
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Regarding the "non-compressibility", my thought would be achieving the bolt tensioning values/ clamping force, while maintaining dimensions, would be complicated by including a ply with low compressive stiffness.
 
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It does seem like an overly complicated assembly, I also share reservations about a compressible material being used. Even if you do manage to get the minimum bolt tension required, over time it may creep as shim deforms.

I've never been that keen on slots across the width of the member like in the angle as you're removing a significant portion of the cross sectional area in doing this.

I can't help but think this arrangement is a good example where possibly allowing the contractor to drill the holes on site once your assembly is in position to get the best alignment. Then you wouldn't maybe even need to specify slip critical bolting. Drill through channel, steel shim and angle all in one go for near perfect alignment. A good contractor might even be able to match drill at least one of the bits before putting it in the final position to avoid or minimise any tolerance issues.

 
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What is the connection at the building to prevent cold transfer? or is it an issue... in this neighbourhood, it is.

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

-Dik
 
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Here in Quebec I don't think we officially have to take into account thermal bridging yet (the new energy efficiency code should be out this summer). However, the architect has hinted at requiring a thermal break, so I got a couple of quotes from fabreeka and steel supplies co. for 3/4 inch or 1 inch thick. Any thoughts?
 
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For drilling on site, I hate to drill into galvanized steel, but this could also be an option. I checked the max. tolerance this morning, and I could reduce the slots on the angle to the dimensions of am oversized hole (13/16" long). However, the long slots on the channel need to stay, the in-out is our biggest variable.
 
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