Bottom rebar in slab over steel deck - clear cover?

[jittles]

I have a 6" total thickness slab over steel deck (4.5" concrete over 1.5" B deck) that has been designed for forklift loading. Following SDI's (Steel Deck Institute) guidelines, the deck is form-only and reinforcing has been provided to support the forklift loading.

The bottom rebar is intended to be in a low flute, with a little over 1" clear from deck to bar. The "d" depth of the bar is 4-1/2" from the top of the slab. Obviously this is my primary design concern - I want to maintain this effective depth.

At some locations, headed studs and spliced bottom bars result in the bars being pushed up against the side of the flutes (still maintaining the correct "d" depth and cover below), which means some of these bars no longer meet ACI clear cover of 3/4".

A couple of questions:


Is anybody aware of any guidance on bottom of deck clear cover for a slab on steel deck? ACI does not specifically address slabs on steel deck and SDI seemingly references ACI clear cover requirements, but they are clearly aimed at the clear cover to the top of the slab.


Are these bars still effective if they are up against (or very nearly up against) the side of a flute?



I'd appreciate any experience or code/standard references. I've reached out to SDI and am awaiting a response, but I thought I would ask here as well!

Thanks!

 

[WARose]

I've typically worked in corrosive environments, ergo I treat the deck like it's not even there. (Other than providing a form.) Perhaps in non-corrosive environments this isn't so much a consideration.

Are these bars still effective if they are up against (or very nearly up against) the side of a flute?

I would think only partially.....because they cannot develop on one side. You would also not be observing minimum cover requirements (as per the "corrosive environment" approach).

 

[dik]

Most deck manufacturers do not recommend their decking be used for moving loads... unless the deck is used as a concrete form. For non corrosive environments, I've used a bar placement to suit the 'flutes' with the support bars bearing directly on the deck.

Dik

 

[jittles]

I got a response back from SDI:

Reinforced concrete slabs using permanent steel deck for forms must be designed in accordance with ACI-318. There is no exception for that in any of our Standards

So proper ACI concrete cover is required period. Bars laying directly on/against flutes would NOT be OK.

I'll be approaching this by getting the bars shimmed off of the sides of the flutes while eating into the allowable 3/8" tolerance on effective depth and clear cover.

 

[dik]

Jittles... by placing the bars in the flutes, I've achieved concrete cover as required... I'm happy, others may not be...

Dik

 

[wannabeSE]

Have you considered a 2" deck? They typically have much wider flutes that will allow more room for the studs and the bars to be lapped.

 

[KootK]

Interesting dilemma. I'd not considered this before. You could also not carry the bars over the beams if the beam spacing is large enough for that to be somewhat sensible.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.