Elevated Slab Crack Control

[DCBII]

I'm designing an 8" elevated slab over metal deck. I'm designing the steel floor beams to be composite with the slab using shear studs. I'm designing the slab to have flexural steel (rather than using the metal deck itself as flexural reinforcement). I'd like to place the flexural/minimum ACI required steel in the center of the deck (3.25" from the top surface) so that it acts as positive and negative flexural reinforcement. Will this be enough reinforcement to control cracking in negative moment regions (such as over the tops of beams), or does it need to be closer to the top surface? This slab will not be covered by carpet (industrial facility), so the owner will see the cracks.

 

[hokie66]

It depends on what you mean by "control cracking". The minimum amount of crack control reinforcement will indeed control the width of the cracks, but it won't prevent cracking.

 

[grantstructure]

Crack width is dependent upon depth to steel, as well, so pushing your steel down isn't going to help.

That's a very thick slab to be casting if you don't need the depth for flexure, as evidenced by not needing to have the steel deeper in your section and using only minimum steel. Are you not using composite deck because of the environment you're in or something?

 

[hokie66]

I should have read closer. Agree with grant that an 8" slab should have reinforcement top and bottom. If the deck is non-composite or deemed to be non-composite, then use two layers of reinforcement.

 

[DCBII]

I think you've both answered my question. I'll place 2 layers of steel in the slab, one close to the surface and one near the bottom.

Now that you've pointed it out I don't know why the slab needs to be 8". I'm using a reference job for this job and the reference had an 8" slab. I'll look into that a little closer.

As far as composite deck goes, I don't know if it's available in the Gobi Desert of Mongolia (even if I specify it on the drawings). I'd rather leave a little fat in the design just in case.

Thanks.

 

[grantstructure]

Enjoy some airag for us. Bonus points if you post pictures from the top of the Turtle Rock.