Coring Elevated Concrete Floor Deck 2

[vmirat80]

Contractor wants to drill 4-inch diameter holes through a second floor concrete/metal pan deck for conduit. Deck span between floor beams is about 8 feet. At what point do these holes compromise the strength of the deck?

 

[Ron]

If you miss the rebar, a hole this size has no effect. Even if you hit the rebar, it will have little effect unless the floor is highly loaded.

 

[KootK]

With penetrations of that size, it comes down to how many, how tightly spaced, and oriented in which direction.

Some docs of interest:

ASC Floor Deck Design Guide

HILTI Openings in Composite Decks

Both documents are freebie reflections of the Steel Deck Institute information which is solid, as you'd expect.

 

[Tomfh]

At what point do these holes compromise the strength of the deck?

You tell me.

 

[vmirat80]

KootK, thanks for the docs, very helpful! Unfortunately, they still leave a lot to be figured out.
- If there are four 4-inch holes running perpendicular to the deck flutes, how far apart can they be from each other so that they don't count as one big opening? My guess, based on their rules of thumb, is that if the holes are spaced so that there is at least 12 inches of deck between them, then they are considered individual holes, assuming the holes are 6-inch diameter or less.
- It seems these documents are written with the assumption that the deck is a composite construction (concrete and metal pan acting together). The floor deck I'm dealing with is not.
- I tried to get the SDI white paper "Deck Damage and Penetrations" but their web site says it's been withdrawn.

 

[jayrod12]

So the steel deck is just formwork? Then it would be up to you to analyze it the same as a concrete slab without the deck. Can they accurately miss teh reinforcing? If so, I don't expect it to be much of a problem from a flexural perspective. It would be up to you to see if it has implications for the shear capacity of the slab.