Small Gap Between SOG and Footing

[Jimbio7]

I have a situation where there is not much space between the top of footing and underside of a warehouse slab on grade (55mm). At this stage it is likely too late to change the steel (pre-eng) and I would rather not add a little plinth to the footing to increase the gap but could if absolutely necessary.
I don't think the standard granular will compact well with such a small layer so I was considering using a clear stone aggregate or just filling the gap with concrete.
Anyone have thoughts or experience with such a small gap?

 

[EcoGen]

Has the SOG and footings already been poured? If not, why don't you just thicken SOG at footing and have it bear directly on the footing?

EcoGen Consultants
Structural Engineers
ecogenconsultants.com

 

[JoelTXCive]

You could put some stabilized sand down to fill the void space.

Or, just pour the slab thicker in that region.

Is there going to be a layer of poly under the slab? I think you would want some sort of bond break between the slab and the footing. A layer of poly could serve as a bond breaker.

 

[Jimbio7]

No poly so I was a bit worried about the bond between SOG and footing but I suppose I could just ask for some poly placed over the footings. There are just a few locations where this condition occurs (most of the slab is 150 thick).
I was also worried about the differential settlement between the hard point of the footing and the rest of the SOG which is why I thought to add at least a little bit of compressible material in the gap.
Nothings poured but excavation is starting now.

 

[HTURKAK]

If i were in your shoes ,

I would prefer to add a little plinth to the footings so the gap in the range of 12-15 in. If not possible, i would go with fine sand ..

I will not suggest to pour the slab thicker in that region since SOG could develop cracks around these regions.

 

[skeletron]

In consideration of least-work principles: probably pour the footing, do your SOG prep, and then pour the SOG slightly thicker in that region. Or pour the footing to u/s of slab.
You could specify 3/4" crush or stabilized sand as per above, but I think in reality you'll get like 2 or three rocks, or sand that can't really be compacted, and I don't think that's doing anything for you at the location.

 

[EcoGen]

I was also worried about the differential settlement between the hard [ignore]point of the footing and the rest of the SOG[/ignore] which is why I thought to add at least a little bit of compressible material in the gap.

I don't think 2 inches of compressible material is going to resolve any potential differential settlement cracks either way. 1 foot below the SOG you have a rigid element that won't compress much at all and everywhere else you have several feet of soil that can compress over time.

EcoGen Consultants LLC
Structural Engineers
ecogenconsultants.com

 

[CRQUT]

Just thicken the slab over the footing. If its going to crack, itd be around the column, which should be either isolated or in a pocket detail. Ask the contractor if the steel will turn up on site before the slabs poured, this could dictate a pocket in any case.

Unsure if you need trimmer bars in a fibre slab, id prob still put them in but you could always ask the fibre rep, im sure he/she would have seen it all before.

 

[dik]

Thickining the slab, may just move any cracking out a bit if it's going to happen. It's nice to have a bit of a buffer.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik