Conduits bundling together horizontally in slab 2

[RDR89]

Hi all, I have an equipment foundation that the contractor wants to embed some conduits in (max. 3" diameter, i.e. OD = 3.5"). I am following general ACI guidelines for putting them in the middle third of the slab, not interfering with the compression area, not putting them on the bottom mat, using 3*d spacing, etc. (although I believe they have removed this specific guidance from ACI 318-14, but did find it in ACI 314). I have perused this forum and found a lot of good threads on conduit placement running horizontally in slabs, however none of these address what happens when the conduits all have to go the same place. It's one thing to have them placed and spaced throughout the slab as ACI recommends, but they all terminate at the same location and I am trying to avoid having them "bunch up" so that there are no honeycombs, no conduits on top of each other, etc. Has anyone run into this problem with conduits all terminating at the same location?

For context, there are (4) 3" conduits and (2) 3/4" conduits total. I haven't run the numbers but I am thinking that the slab would need to be at least 18" to meet the middle third requirement and the 1/4 slab depth requirement for conduit size. The total equipment weight is only around 5000 lb but the equipment is ~87" tall and ~42" wide so there is some wind load to consider.

 

[JoelTXCive]

Can the contractor go under the slab and then pop up at the destination point?

When I have large concentrations of conduit coming together at one point, I conceptually, treat the whole area as a hole in the slab. Depending on the size, sometimes I even detail it as a hole with diagonal bars around the region. Then, I don't worry about what happens inside the hole.

 

[RDR89]

No unfortunately they want it embedded. Design wise I am definitely going to consider the area as a void. Unfortunately, the piece of equipment that the conduits are all terminating into also needs to be anchored on the slab so I need to keep enough concrete in there for the anchorage or find a way to anchor it such that it still sits on the slab.

 

[KootK]

In the past, I have deliberately bundled conduit in areas of high congestion in order to improve matters. The photos below show what difference that can make in certain situations.

 

[RDR89]

Wow @KootK that photo is something... did you size the slab based on the total height of the largest conduit bundle then? What was your largest conduit?

 

[KootK]

did you size the slab based on the total height of the largest conduit bundle then?

No, this was a condition that was only recognized during construction.

What was your largest conduit?

No idea, the photos are from 2008.

 

[bugbus]

What size are those top beam bars?