Electrical Conduit Embedded in Elevated Composite Slab

[Loui1]

What are the general rules about embedding conduit in composite deck / composite beam slabs? I see nothing that says yay or nay and only calculations of the composite action on every beam and deck span seems to be the answer.

The electricions who did this claim that it is very normal to place bundles of 10 conduit in these slabs which I find very hard to believe and prove that it works.

SDI doesnt appear to cover this issue, any help is appreciated.

 

[MotorCity]

Loui1,
I usually allow pipes, conduits, etc. to be placed within the flutes of the metal deck as the concrete in the flutes contributes very little to composite action. Assuming you have at least a 1 1/2" deck, the electricians are usually willing to work within the flutes and around the headed studs.

 

[jike]

Refer to ACI 318.

Bundled conduit should not be allowed. The conduit needs to be spaced out adquately to allow concrete between conduit. I recall correctly, spacing needs to be 3 diameters.

I do not allow conduit to be tied to studs or directly adjacent to them. Conduit never should be allowed to displaced reinforcing. It is often not practical to locate conduit in flutes since it many times needs to run diagonally.

I hope this helps.

 

[JAE]

MotorCity - a lot of composite decks have their primary indentations (ripples?) located in the flutes, which provide the primary bond mechanism between deck and concrete. Primary failure of composite decks is shear bond failure between metal and concrete.

I would think that keeping conduit in the main portion of the deck, and spaced out as jike states, as the best option.

Your thoughts?

 

[Loui1]

ACI 318, Ok, I'll check again to see if there's anything about embedments.

JAE, I agree. I would like to hear the reasoning also. There are two main issues I see.

1. Placing conduit within the compression zone of the composite beam will reduce the beam's capacity. Especially if the conduit is running parallel to the beam, you effectively reduce the concrete area. Will it fail? probably not unless you have a huge bundle of conduit. It might crack. But really its a, "how would you prove it in court" type of thing.

2. Placing conduit down in the flutes of the deck will reduce the composite action of the deck.

 

[MotorCity]

JAE,

Thats a good point about maintaining the steel-concrete bond. I guess the way I think of it, you're really not taking a huge reduction in the area for the steel-concrete bond. (Theoretically, a round conduit is only tangent to the deck along a line.) I prefer the conduit in the flutes as long as it is not in bundles (2 conduits max)and always try to minimize the number of flutes with conduit. This way, the studs and reinforcement (if any) can be fully utilized without interference with conduits. Actually, I do not receive requests from contractors very often to do this as most of my projects have drop ceilings and/or cable tray for hiding conduit.

 

[WillisV]

ASCE 3-91 provides guidance for this.