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Metal Deck to Concrete Attachment

Metal Deck to Concrete Attachment

(OP)
I have a project that consists of infilling some existing skylights made in a precast T structure with metal decking. From what I can tell I have two options for attaching the metal decking to the existing precast T's

1) attach a continuous bearing plate around the perimeter of the opening and attach the decking to this plate (by shooting the deck to the plate with Hilti fasteners as welding is not allowed)
2) Use Hilti fasteners to attach the deck directly to the precast T.

Option 2 makes the most sense as we will need to do the fastening by some sort of Hilti shot anyway and I think the shot will do less damage to the Precast T. My question is in regards to which of Hilti's fasteners are best suited for this condition?

The project isn't exactly real yet so I am holding off on contacting Hilti. Just trying to do a little leg work before the project moves forward.

RE: Metal Deck to Concrete Attachment

Are you trying to attach to the precast T flange? If so it is pretty thin concrete and so it is difficult to get sufficient embedment for anchors.

Are you thinking that the plate, that you mention, fastened to the bottom of the precast flange? If so I do not recommend fasteners in tension, especially with very little embedment.

Are you thinking to bear the metal deck directly on top of the precast? If so, how will you provide adequate thickness of insulation without a bump in the roof?

Is there any fire rating to consider?

Consider a Z shape member on 4 sides with its top flange bearing on top of the precast so the deck could bear on its bottom flange. Thru bolt precast flange to anchor Z shaped member.

RE: Metal Deck to Concrete Attachment

A bit of a caution. The precast concrete is hard and brittle due to the high strength. I've encountered difficulties with HC slab, and, I think 'some' supplier manufactures an anchor specially for high strength precast. I'll try to recall the name of the supplier.

Dik

RE: Metal Deck to Concrete Attachment

Why the decking? If you can form inside the opening, forego the deck & just infill with concrete.

RE: Metal Deck to Concrete Attachment

Decking infill may be less expensive?

Dik

RE: Metal Deck to Concrete Attachment

(OP)
The thought process is to use metal decking to speed up the construction progress. The deck would be placed on top of the beam and but the anchors would be in tension (to resist roof suction issues). I'm not sure of the magnitude of the load, but if I had to guess I am talking about 50-80plf (allowable) around the perimeter of the opening as the span isn't that large.

RE: Metal Deck to Concrete Attachment

Maybe you could use 1/4" x 1 1/4" hex head tapcons? It seems like you just want to keep the deck from moving around during construction. These are placed in small drilled holes and bite into the concrete without the outward force of an expansion anchor.

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