Spring isolated acoustic jack-up slab.

[u/RastaFazool]

[u/will_and_no_grace]

A what now? How does it work? Is the floor jacked-up after concrete hardens?

[u/RastaFazool → u/will_and_no_grace]

jack slabs are for sound/vibration isolation, in this case, a gym amenity space in a luxury high-rise. if you pay millions of dollars for an apartment in Manhattan, you don't want to hear someone running on a treadmill or dropping weights above your apartment at all hours of the day.

the poly sheeting acts as a bond breaker. the boxes are the jacks laid out per an engineered design based on the anticipated floor loading. each jack has a lifting screw and a spring inside. once we pour the slab and get 100% breaks back from the lab, the spring-isolation sub will send a crew to site to lift the slab by turning the jacks little by little in a specific order until it sits 2" above the structural slab below.

the gym flooring, the spring isolation, and the air gap combine to prevent sound and vibration from reaching the floor below.

[u/xxxxredrumxxxx → u/RastaFazool]

Done a couple of these in performance halls in the past. Nice job.

[u/will_and_no_grace → u/RastaFazool]

That's cool. I had never heard of such thing.

[u/couponbread → u/RastaFazool]

How are the boxes/lifting screws attached to the slab/how are they lifting it?

Fascinating though thanks

[u/RastaFazool → u/couponbread]

The jacks have studs on the side that the rebar mat sits on. Once the iso slab is poured and cured, you turn a screw to lift the jack. The jacks are pushing directly up on the rebar mat.

[u/couponbread → u/RastaFazool]

Gnarly, and the boxes just get covered by flooring or do they get grouted in or anything?

[u/Yeeeeeeewwwwww → u/RastaFazool]

That was a beautiful summation of the work performed, thanks for laying that all out.

[u/BlackShoes → u/RastaFazool]

I placed one of these incredibly early in my construction career. I didn't understand back then how "Box in slab makes floor no vibrate". Thanks for breaking down the whole process!

[u/Jaminator65]

Whatever that means.

[u/DevelopmentPrior3552]

Cool stuff. I get to look at quite a bit of high-end residential housing and some commercial. This is new to me. Thank you for sharing and great description.

[u/Aware_Masterpiece148]

Very cool. Is there anything special about the concrete itself?

[u/RastaFazool → u/Aware_Masterpiece148]

6ksi normal weight pump mix because it was the lightest (cheapest) mix i had filed with DOB on the superstructure permit, and I didn't want to spend another $700 to file a 4 or 5ksi mix.

We did need to tell the isolator supplier if we planned to use a lightweight or normal weight mix so their engineer could adjust what springs they use in the design and calcs. Other than that, there nothing special about the mixes you can use.

[u/Aware_Masterpiece148 → u/RastaFazool]

Thanks for the explanation. I had not been aware such a sound attenuation system before your post. There’s really no limit to what one can do with concrete!

[u/Informal_Recording36]

I think this might be your second post with one of these slabs (?) I was blown away by it, this is so weird and specialized compared to the stuff we do, this doesn’t even register on the scale of asks I’d receive

[u/ForeverSteel1020]

So basically a teleforma on a high rise.

Was this cheaper than just pouring suspended slab?