Floating slab detail where it gets "toothed" into concrete fdn wall

[theclipper]

I have a client who has another building on campus where the interior slab on grade detail was totally floating and there is significant amount of floor finish cracking around the perimeter.

They really want me to tie the simple 4" slab on grade into the fdn wall. There is 8" masonry above the 14" concrete foundation wall. Has anybody ever toothed the slab into the masonry to hold it in place? I'm inclined to think the problem slab was subjected to warping/curling due to poor detailing/curing etc....during the first construction. What do you guys think?

 

[Ltwine]

I think your inclination is more correct.

 

[ToadJones]

I dont think it will hold it in place anyway. Concrete will shrink as it cures and pull away from the key.

 

[paddingtongreen]

Is the edge of the slab curling upward or downward? Is there any sign that it has settled relative to the wall. I ask because the fill around the footing may have been properly compacted, but the interior might have just had the top cut from the existing dirt. In that case, tying it to the wall would make the edges become a structural slab if there is more interior settling.

Michael.
Timing has a lot to do with the outcome of a rain dance.

 

[CTSeng]

They never understand "the customer's always right" adage doesn't apply to their structural consultant. However, if you have to tie the slab into the foundation wall just be sure there is plenty of reinforcement dowelled out of the wall extending some distance into the slab to hold the cracks tight together.

 

[BAretired]

If the subsoil is a swelling clay, tying the slab to the foundation may cause the masonry wall above to lift and crack. From that standpoint, it would be better to let the slab float.

Alternatively, you could tie the two together but provide a voidform under the slab for two or three feet adjacent to the wall.



BA

 

[hokie66]

What floor finishes were cracking in the other building? Isn't it easier to deal with cracking in floor finishes at the edge than in the middle? Restraining a lightly reinforced slab on ground will just shift where it cracks.

 

[woodman88]

I have doweled a ground slab, around a pool, to a concrete wall with exterior floor slab. The client did not want a tripping problem as the ground compressed. The ground slab was thicken and reinforced to span 10 ft. from the wall. But this was for a large apartment complex and the added cost to the project was minimal.

Garth Dreger PE
AZ Phoenix area

 

[Ltwine]

Rather than tie into existing structure which can have other complications, why not consider:

1. Seal the cracks and observe.
2. Add a thin layer of light weight topping (after repair).