# Cast-in Unistrut / Conduit supports



## adonkle (Jun 10, 2014)

Primarily a curiosity, but on several jobsites recently I've noticed long conduit and pipe runs down corridors supported from Unistrut cast into the bottom of concrete floor slab for the floor above (or cast into the underside of the roof slab). As opposed to drilling supports in later, I can see the advantage of cast-in supports. 

I'm curious how these types of supports get coordinated when the slabs are being poured, as I've never seen them show up on contract drawings before and the supports I've noticed often seem to be shared between conduit, plumbing, and fire sprinkler pipes. Do some GC's just know to provide support points like these for multiple people to use, or does someone typically request them specifically?


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## Rollie73 (Sep 19, 2010)

If its a large cast in place concrete job or even on tilt up projects, I will usually have a man or two on site setting any boxes, supports and pipe in the forms that we can before the pour is done. It saves huge amounts of time.
FWIW.....the mechanical guys do it here as well. We will also try to lay out and block in any areas that require a pipe chase or where we will have to pass through a cast in place floor deck......it saves lots of time and money spent on core drilling.


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## CTshockhazard (Aug 28, 2009)

I've seen them in some fairly old buildings around here.

Sure beats drilling overhead, then setting an anchor, then bolting up the strut.:thumbsup:


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## CADPoint (Jul 5, 2007)

My belief is that not many here can give you any formula as to when you could or couldn't use unistrut in concrete.

This is why there are Structural Engineers. 

Here a layman's overview!
There is quite a bit of information that is used to design and load a floor.
The design load of a floor works as a unit, everything in that area is considered to get the desired results for the potential loading. 
Adding material that is not meant for any loading properties and is in fact foreign to a floor and has no physical loading characteristic thus is a deduction to the physical load characteristic's desired.

As a side note to consider; the loading and getting the desired physical properties of a concrete floor can be designed for both the top and or bottom of the thickness of the floor. 
Say its on grade only the bottom of the slab gets reinforcement to withstand all the load that works on all of the thickness of
the concrete till it sees the reinforcement that spreads the load farther away from the exact load above thus not breaking through the thickness of a slab.

When one has a raised factory floor it's loaded with reinforcement on both the top and bottom of slab, the top reinforcement with help with the loading of weight above while the bottom carries the load of the weight of all the floor and the helps stabilize the load above as well.

concrete floor load capacity

PSI floor loading for industrial floors


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## macmikeman (Jan 23, 2007)

CADPoint said:


> My belief is that not many here can give you any formula as to when you could or couldn't use unistrut in concrete.
> 
> This is why there are Structural Engineers.
> 
> ...



Given that the same equipment load will be suspended either way , adding the strut afterwards imposes even more single point stress on the ceiling slab because the three or so drilled and driven bolts supporting the strut onto the ceiling do not spread the load as evenly as the poured in place struts. However, seeing some loads suspended the way they are has had me think it would be much safer if those submerged unistrut bars had additional support before the concrete is poured, such as bolting to the rebar grid for instance.


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## adonkle (Jun 10, 2014)

Rollie73 said:


> If its a large cast in place concrete job or even on tilt up projects, I will usually have a man or two on site setting any boxes, supports and pipe in the forms that we can before the pour is done. It saves huge amounts of time.
> FWIW.....the mechanical guys do it here as well. We will also try to lay out and block in any areas that require a pipe chase or where we will have to pass through a cast in place floor deck......it saves lots of time and money spent on core drilling.


Interesting. Assuming there's no equivalent way to do this with precast jobs?


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## Rollie73 (Sep 19, 2010)

adonkle said:


> Interesting. Assuming there's no equivalent way to do this with precast jobs?


I have never done a precast job so I would have to say NO...:laughing:


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## freeagnt54 (Aug 6, 2008)

I've seen it a few times and I believe it was designed/engineered into the building. It ran the width of the building every four to eight feet depending on the area and two rows down the columns and specs included elvation zones for your pipe. Say your small diameter pipe running N/S was allowed on the "inbed" when you switched direction to E/W you had to drop down 1 5/8", and then below that was N/S and E/W zone for larger diameter pipe. It was nice because you didn't end up with a mess of weaved pipe and saddles and no drilling into the concrete. Although the depth was not always perfect, sometimes making it difficult to strap a pipe directly to it.


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## markbrady (Jun 2, 2014)

more common here to use pre cast hangers for rod and it allows you be able to adjust your heights but you need to be able to lay out very good or better yet have a transit


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## Bad Electrician (May 20, 2014)

When I was a helper we did this or used deck inserts basically a slot in a metal box for a square nut.


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## snorky18 (Nov 6, 2012)

I used to work at a nuclear facility (so this answer may not be very representative of the rest of the world) where we had those UNISTRUT supports cast into most of the walls and ceilings on 48” centers. They were cast in place with concrete studs welded to the back of them every few inches.

There’s at least two advantages that come to mind:
1-supporting (relatively) small items from the UNISTRUT is obviously much faster and easier than having to install anchors, both for new construction and future mods
2-Installing anchors in concrete means you may hit rebar. Installing anchors (any bigger than tapcons) at a nuclear facility means you will very frequently hit rebar, and have to spend time/labor trying to avoid it (since you generally aren’t allowed to drill through it) and you have to rework supports from the original design when you hit rebar unexpectedly, which consumes a lot of time, money, and frustration.

As far as how the usage of the supports is divided up, in general the bigger stuff that was designed and routed on paper (piping supports, HVAC supports, larger conduits) was planned in advance, and (obviously) had precedence over the field routed stuff. The smaller field routed stuff was more of a first come first serve basis, but there was generally plenty of strut space available at that facility.

In terms of weight bearing capability, that stuff is hellaciously strong, so in general the items that we field supported with it were small enough loads compared to the overall strength that it rarely even required a detailed analysis.


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