Top rebar in structural slab in unheated building.

[RHT2020]

Hi, I am designing a "doghouse" building with structural slab on void form and supported by pile system. The building is unheated year round. I have designed the slab with bottom reinforcement and slab thickening at the perimeter of building. Do you think I need top rebar in the slab for any reason? Thanks.

 

[r13]

What is a "doghouse" building? Open to ambience/atmosphere environment? Shrinkage should usually be the concern.

 

[atrizzy]

I would imagine the presence of piles induces negative moment in your slab, and that therefore you'll need top steel.
How did you design your slab?

 

[RHT2020]

Hi retired13, it is a shed building in rural area with concrete pad and wood frame building on it.

Hi atrizzy, I have grade beams at the perimeter of building between piles. I have L dowels from the grade beam to the slab all around top.

Thanks.

 

[r13]

I would rather reinforce the top face and save the bottom.

 

[RHT2020]

retired13, it is structural slab. I don't think bottom rebars can be saved.

 

[r13]

I don't know the specific function of the doghouse, but if you think the slab has structural function, why reinforce one face only? To me, the top face is more important than the bottom, that is not exposed to whether, and view. By the way, I think the slab should be floating type (not rigidly cast together with the grade beam).

 

[jayrod12]

If there's no intermediate supports, then no you don't need any top reinforcing except perimeter dowels in my mind. How large is the doghouse/shed? How deep is your slab?

 

[RHT2020]

Jayrod12, footprint is 14x20feet. my slab is 7" with 18" deep grade beam around.

 

[jayrod12]

That's an L/D of 20. Pretty tight for a simply supported slab.

But still, that being said, there are many a structural slab out there that have no top steel in the middle/middle strips. From a strength standpoint it would not be required. From a serviceability standpoint, that's a different animal. With that L/D you may run into long term deflection issues depending on the internal usage of the building. And if there are some shrinkage cracks they will be random and go unchecked. Top reinforcing would at least keep them to a manageable width.

 

[r13]

Why the use of void form? Do you have expandable soil onsite?

 

[atrizzy]

retired, I suspect this might be a frost heave issue due to it being an unheated building?

 

[r13]

Maybe, so a doghouse on pile