Parking Deck Structure

[Pierre C Belarge]

I have a few pictures of a parking deck structure wiring method. There are control joints in the deck every 25ft and there are expansion joints every 75ft. I would like to know if you think the method complies with code or it does not comply with code.
(notice the terms in itallics)



All 3 pictures are of the expansion joints. Notice the wiring method installed.

 

[iwire]

It is a violation of common sense but I do not know of any code violation.

 

[KevinVost]

IMO, there is no allowance for the conduit to "expand"/move as the structure shifts/settles and as vehicles move through the garage. As close as I can get is 300.10. The install could* be pulled apart or loosened which would be a violation of 300.10, and possibly void its use as provided for in 250.118. (*I know we don't inspect could haves.)

Without a specific code to cite, I don't think you can call it a violation. I think most would agree it is an install that could have used a little more planning.

 

[ronmath]

IMHO 300.7(B) would apply. FPN refers to table 352.44 and 355.44. 352.44 states expansion fittings are required for expansion greater than 1/4" due to thermal conditions. I suppose you could make a case that if the thermal contraction expansion of the concrete is greater than the metal you would need expansion fittings, otherwise it would have to be calculated using the method described in 300.7(B) FPN. In short I don't think you can tell from the pictures weather it complies with this or not. Provide calculations to support the method.

 

[KevinVost]

IMHO 300.7(B) would apply. FPN refers to table 352.44 and 355.44. 352.44 states expansion fittings are required for expansion greater than 1/4" due to thermal conditions. I suppose you could make a case that if the thermal contraction expansion of the concrete is greater than the metal you would need expansion fittings, otherwise it would have to be calculated using the method described in 300.7(B) FPN. In short I don't think you can tell from the pictures weather it complies with this or not. Provide calculations to support the method.

IMO, I don't think you could apply 300.7. It specifically discusses thermal expansion and contraction and what Pierre is looking at is the movement of the structure, although I like the angle you presented.

 

[Pierre C Belarge]

IMO, I don't think you could apply 300.7. It specifically discusses thermal expansion and contraction and what Pierre is looking at is the movement of the structure, although I like the angle you presented.

Actually he "hit the nail on the head"

This is exactly what I was looking for, I wondered how many other inspectors/installers have been required to install expansion couplings at these type locations.

The reason for the expansion joints in these structures is for movement based on thermal expansion and contraction of the concrete.
As Ronmath explained so well, concrete and EMT do not have the same expansion/contraction ratio, which we all know can and most likely will lead to an issue with the EMT.


In some of the parking structures, the raceways cross at least 4 of the expansion joints as they are installed. I see this as non-compliant based on 300.7(B).
Seeing as we have a 100F temperature swing here during the year, this could be significant with the concrete.

 

[iwire]

IMO, I don't think you could apply 300.7. It specifically discusses thermal expansion and contraction and what Pierre is looking at is the movement of the structure, although I like the angle you presented.

My first thought was exactly that Kevin, but then I was thinking that the reason the parking deck moves is due to thermal expansion and contraction.

Ron may be on to something, I am still fence sitting on this though.

 

[Pierre C Belarge]

My first thought was exactly that Kevin, but then I was thinking that the reason the parking deck moves is due to thermal expansion and contraction.

Ron may be on to something, I am still fence sitting on this though.

I hope the fence is not too comfortable.

 

[Pierre C Belarge]

I am not the inspector of record for this structure and the other 3 that are on this property. If I do the math correctly, there are about 450, maybe more, locations where the pipes cross the expansion joints.

There are other issues here as well, grounding transformers to isolated pieces of metal, exits signs supported incorrectly, Raceway fill, box fill, etc...

 

[iwire]

Generally job specs require expansion fitting wherever raceways cross building expansion joints. Kind of surprised the engineer on the job has not picked up on this.

 

[MarkyMarkNC]

concrete and EMT do not have the same expansion/contraction ratio, which we all know can and most likely will lead to an issue with the EMT.

But this is going to be true regardless of whether there were expansion joints in the concrete or not. The actual amount of expansion of the emt is going to be the same regardless of the concrete expansion joints, and vice versa.

If the expansion joint was the only place the concrete was expanding to it would be one thing, but we all know the concrete is going to be expanding uniformly along its entire length or width.

The coefficient of expansion of concrete is MINIMAL compared to steel. The reasons expansion joints are put in is due to the extreme forces expanding concrete can produce over small distances. In my opinion, these expansion joints are a non-issue.

 

[ronmath]

I might tend to agree with MarkyMark that the expansion joints in the concrete themselves are maybe a non issue, that does not mean it's a compliant install however without conduit expansion joints. If in question (which it seems like it is) have the engineer provide the calculations showing less than a 1/4" expansion/contraction for the length of runs in question. Just using the "rule of thumb" listed in the code pertaining to table 352.44 (.2 * factor in table 352.44) you get .00812" of expansion/contraction per foot of conduit at a 100 F change. .25"/.0082"=30.78 feet of conduit. Any runs longer than 30 feet would require (by code) expansion fittings and bonding jumpers. IMHO Good design however might require them anyway.

 

[steve66]

Although the conduit expansion will be much more than the concrete, I think it will probably be distributed along the pipe's length, and either absorbed at the couplings, or the pipe will bow between the mini's. (From the handbook, I get less than 0.1" of expansion for every stick of conduit.)

But that expansion joint has to absorb the movement of the entire 75' of concrete all at one spot. It's going to be hard for that to be passed through the mini's (unless the mini's are left a little loose) so the conduit will have to absorb it all at one place.

I think it could be a problem, but it's hard to say for sure.

 

[elohr46]

I have a few pictures of a parking deck structure wiring method. There are control joints in the deck every 25ft and there are expansion joints every 75ft. I would like to know if you think the method complies with code or it does not comply with code.
(notice the terms in itallics)



All 3 pictures are of the expansion joints. Notice the wiring method installed.

How can you tell from underneath the slab if that is indeed an expansion joint? What does the top side look like? Is it caulked for expansion or poured concrete to join the slabs together? I have seen it done both ways and to tell you the truth I don't recall the specs asking for expansion fittings in either case.

 

[cowboyjwc]

The last one we did here they just ran smurf tube and the boxes in the deck so they didn't have any exterior pipe. That and we have earthquakes, thermal expansion is the least of our worries. We don't move, inches we move feet.

 

[Jim W in Tampa]

The double T's are common here. They are welded then calked. As long as they are welded it is 1 building and i see no more of a problem than if it was one large building. Did one about year ago that was exstention to another, the 2 sides were not welded and used sealtight for runs between them. You might have problems we did not have because of location and feezing.

best add that you will get movement all day long with cars.

 

[Volta]

The reason for the expansion joints in these structures is for movement based on thermal expansion and contraction of the concrete.
As Ronmath explained so well, concrete and EMT do not have the same expansion/contraction ratio, which we all know can and most likely will lead to an issue with the EMT.

I don't think that steel (EMT) and concrete (in general) have very widely separated coeffiecients. Same order of magnitude, at least, I think.

I believe the length of runs and 300.7(B) to could be looked at for compliance.

One could interpret 300.7(B) to consider the "expansion and contraction" of the mounting surface in addition to the raceways. That might necessitate expansion fittings.

But it does say "where necessary" . . .

IMHO 300.7(B) would apply. FPN refers to table 352.44 and 355.44. 352.44 states expansion fittings are required for expansion greater than 1/4" due to thermal conditions. I suppose you could make a case that if the thermal contraction expansion of the concrete is greater than the metal you would need expansion fittings, otherwise it would have to be calculated using the method described in 300.7(B) FPN. In short I don't think you can tell from the pictures weather it complies with this or not. Provide calculations to support the method.

I agree with ronmath, 300.7(B) should do it.

FPN = 352 > 1/4" for those two non-metallic types, unspecified for metal.:smile:

 

[Smart $]

I agree with ronmath, 300.7(B) should do it.

It does... but only one side of it.

The other side is the coeffient of thermal expansion [CTE = (ΔL/L0) / ΔT] of concrete. According to this webpage the CTE range of concrete (4.1-7.3 x 10^-6 per ?F) includes that of steel (6.1-6.7 x 10^-6 per ?F).

So, depending on several factors, there could be no difference in expansion and contraction between the conduit and concrete, or some difference, but less than 300.7(B) FPN and associated articles makes there appear to be. Without a lab-based evalution, it's a shot in the dark :grin:

 

[quogueelectric]

Have done tons of these and always used pvc. Some poured slab jobs are called fillagree which is about a 3-4 inch pour of concrete on the top of the slabs.