Floor Slopes in Structural Slabs

[KarlT]

I have a 7" main floor structural slab over 6" void form (no crawlspace required). The interior portion of the slab is supported off a grid of cast in place concrete friction piles c/w drop panels.

Now, there are some areas that will require floor drains, and four finished sloping sides to each drain. This results is a smaller slab depth, which theoretically reduces your "d" to a minimum at each floor drain location. (Assuming the slope is say 1-2%, that could result in losing 1-2" of depth at the drain area) Is there some way of allowing the bottom of the slab to remain at a constant elevation and still design the slab to account for the floor slope?

 

[boo1]

Thicken the entire slab, using the min t at the drains.

 

[JAE]

...what boo1 said,
OR,

...you could just require the preparation grading to slope with the floor slab and provide a uniform thickness. With slight slopes like this, the rebar will simply turn and slope gradually with no specific bending required.

 

[Focht3]

Why the void space?

If it is needed because of potential soil swelling problems, you must maintain the 6 inch clear span below the plumbing lines, too...



Please see FAQ731-376 for great suggestions on how to make the best use of Eng-Tips Fora.

 

[JAE]

Focht3 - cummon...you know that expansive clays just "gush" up around pipes
...except in S.A. TX

 

[Focht3]

... and Dallas, Houston, Shreveport, Jackson, etc., etc.




Please see FAQ731-376 for great suggestions on how to make the best use of Eng-Tips Fora.

 

[boo1]

Would the forming to a slope would cost more than extra inch of concrete?

 

[JAE]

I wouldn't think so - at least no to any great amount. Either way the contractor must set up vertical control and check the final elevations - one is dirt with no time crunch and the other is wet concrete that is rapidly setting up.