Slab Cdts

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horsegoer

Senior Member
Location
NJ
Has anyone ever seen or installed conduits like this?
These are slab on grade.

Not sure why wouldn't just put in the dirt?
Obviously much more labor intensive then laying on ground on chairs/spacers.
 

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gadfly56

Senior Member
Location
New Jersey
Occupation
Professional Engineer, Fire & Life Safety
Looks like this detail was drawn by some junior level student who has never seen a job site in his life. There is no note regarding backfill or cover so maybe this isn't actually in the ground? I'm trying to think how you could cast this in place and then easily remove the form sections and not having much success. Any concrete guys here who might help us out? I've seen where Unistrut is cast into the bottom of a slab for use as support for pipe and raceways, but that's a whole different deal.
 

Todd0x1

Senior Member
Location
CA
This looks like maybe due to soil conditions or something the slab is floating above grade and supported by the vertical concrete walls.

As far as assembly, looks like you would place the pipe first -it would have to sit on something, then add the strut racks with threaded rod poking up, then the carpenters would build the form with the rod poking through holes, then you come back and place the nuts and steel plate.

I am very curious why they want it like this.
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
what is geofoam? and why would there be no soil there?

why would you need to cover it with geofoam or soil if it was floating above grade?

how would you remove the concrete forms?

I am wondering if it is some kind of precast structure.
 

horsegoer

Senior Member
Location
NJ
They are saying the conduits would be concrete encased . They want a deduct to lay the conduits in the dirt.
 

gadfly56

Senior Member
Location
New Jersey
Occupation
Professional Engineer, Fire & Life Safety
They are saying the conduits would be concrete encased . They want a deduct to lay the conduits in the dirt.
If that figure is an illustration of the proposed alternative installation method, I'd tell them it will be 4 or 5X, thank you very much. I won't say this is impossible to construct, but how, for just one question, would you backfill once the slab is in? Lots of guys with shovels? What about compacting the fill? Run the tamper sideways?
 

Rock86

Senior Member
Location
new york
Occupation
Electrical Engineer / Electrician
Seems to me like there is some kind of channel system which may be under the floor in some areas, or like it was mentioned, this may just be a general detail. Note 1, although poorly written does mention to only use the geofoam where the soil doesn't cover it, so backfill it with soil. Also, this detail looks like it should be more for ceiling hung conduits. Seems like it would be expensive to do it that way in dirt.
 

jim dungar

Moderator
Staff member
Location
Wisconsin
Occupation
Retired Electrical Engineer - Power Systems
I see no rebar in the slab or vertical posts. Note 1 incomprehensible. Need nuts on top of the Unistrut if this is supposed to be in mid air when the concrete is poured. And then the concrete guys need to run rebar around this assembly.
The OP detail addresses the conduit support, it does not show the actual concrete and rebar details.

I have seen a similar installation where the concrete deck stuck out from the side of a hill, so part of the conduit run was underground and the rest was in open air, under the decking.
 
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Phillip Land

Member
Location
Rome, Ga, US
Has anyone ever seen or installed conduits like this?
These are slab on grade.

Not sure why wouldn't just put in the dirt?
Obviously much more labor intensive then laying on ground on chairs/spacers.
This is something that I ran across in Charleston a few years ago. The reasoning behind it was that if the soil got washed away in a hurricane or tropical storm then the feeders of the duct bank would not get as easily destroyed and washed away. We installed these on all of the duct banks on a huge multi-use facility. We just made sure to use a transom to determine where the slab was going to be so that the tops of the rods in the rod holders were in approximately in the center of the slab. They were still a pain to install and reminded me a little of the seismic supports needed in earthquake prone areas
 

Strathead

Senior Member
Location
Ocala, Florida, USA
Occupation
Electrician/Estimator/Project Manager/Superintendent
This is something that I ran across in Charleston a few years ago. The reasoning behind it was that if the soil got washed away in a hurricane or tropical storm then the feeders of the duct bank would not get as easily destroyed and washed away. We installed these on all of the duct banks on a huge multi-use facility. We just made sure to use a transom to determine where the slab was going to be so that the tops of the rods in the rod holders were in approximately in the center of the slab. They were still a pain to install and reminded me a little of the seismic supports needed in earthquake prone areas
Interesting. I am glad someone had some idea what this might be about.
 
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