Control joints in composite deck?

[OCI]

I'm working on a 2000sqft steel framed mezzanine with a concrete deck on metal pan. This is the first time I have used this type of floor assembly. Do you typically cut control joints in a composite slab? I have W beams on 8' centers for joists and girders at 16'. Thanks.

 

[lkjh345]

I typically do not. The composite deck restrains the concrete from pulling back at a joint, so its not an effective joint anyway.

I alway use welded wire fabric or fibermesh in my concrete fill to control tempature ans shrinkage cracks.

 

[BAretired]

I have never cut control joints in a slab like that. I agree that it would not be effective, particularly if the deck is composite.

BA

 

[OCI]

That's what I thought. I am using WWF and was considering adding some additional reinforcement at areas of neg. moment to help with cracking there. Thanks.

 

[lkjh345]

FWIW: I usually run #4's @ 16" o.c at the girders. The concrete does tend to crack over the girders due to rotation of the beam spans. I usually set them with 1" clear to the top of the slab. Holds the crack reasonably tight

Oddly, I also tend to get small, but noticeable cracks, over the beams where composite deck sheets start and stop.

Anyone else observe this behavior?

The beams the deck sheets are continous over, generally no crack, but the beams were the deck sheets start and stop, I quite often get cracks. I assume its due to rotation of the deck spans. Just an odd thing I've observed.

 

[hokie66]

lkjh345,

I think that is because the deck is acting as shrinkage reinforcement, and you are making this reinforcement discontinuous at the supports. Not because of rotation of the deck.

Your explanation for cracking over the girders, and reason for reinforcing at that point, is correct.