Inaccessible voids in concrete?

[AaronMcD]

Just wondering if there are any reasons to avoid inaccessible voids in concrete work. Any problems with just abandoning forms in permanent voids?

(Also, can someone ban that annoying bot?)

http://www.hellodwell.design

 

[structuralCADspecialist]

There's many advantages to using voids (avoiding slab steps for one). I've seen many practices usually ranging from bad to terrible. Underneath stairs is common. I've mostly seen engineers dodge the responsibility and just write "void" or "void space" on the drawings. Not a bad approach in my opinion. I kind of wish the concrete industry would create a report regarding the best practices in these situations.

Rigid foam to take up the space (and essentially serve as the bottom formwork) is a good solution but it's expensive. Most of the time I see guys just leaving the formwork in place. I have concerns about this practice in the long term but can't undoubtedly say that anything of real consequence will occur due to it. Especially in colder and/or dryer climates.

Depending on the specific detail drainage holes might be a must-have.

Personally, I'm hoping for a newer more modern/innovative approach to materialize. Looking forward to seeing what the more experienced forum members have to say.

 

[dik]

Some void materials float...

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

-Dik

 

[HTURKAK]

Mr .dik (Structural) has a valid point.. depending on the size of inaccessible void ,Polystyrene board, hollow bricks or plywood forms could be used..

Personally i will prefer to fill the voids with inert materials ( hollow clay bricks / conc. masonry blocks ) if the size large , it is better to provide a 600x600 mm opening to take out the form..

If you specify the void , you may get better responds..

 

[kipfoot]

I think it's a judgement call. My objection would be in exposed cases, like an entry ramp. In this case, it's really just a principle that something that's prone to deterioration should be able to be visually inspected.

There are cases, like a ground level slab over expansive clay, where you might intentionally use a void form and leave it in place. Also, if you were to leave a void under an interior stair landing I'd give it a shrug, though I generally lean toward air flow and access.

 

[dik]

I try to avoid clay with concrete...

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

-Dik

 

[AaronMcD]

The application is an outdoor fire oven under a patio roof. It is a big concrete rectangular box with the front open for cooking at a counter, and a concrete chimney over the top. The larger rectangular box is capped at ~10 ft elevation, but the ceiling of the oven is at ~6 ft elevation. There will be a void between the ceiling of the oven and the roof of the entire box. The entire interior, ceiling and chimney, is concrete to support the oven tiles. I don't want to fill the void with heavy materials because the whole thing already weighs 60 kips in SDC D, and I don't want to intentionally transfer this seismic load into the main structure which is much lighter.

http://www.hellodwell.design

 

[HTURKAK]

The use of ribbed slab with hollow clay blocks is one of the common methods in my region..

So the void depth around 4 ft... I think the formwork can be taken out from an opening .. Pls post some sketch to get the full picture..

 

[dik]

thanks


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

-Dik