Radiant Piping in Elevated Slab

[Steel2Steel]

We have a floor system that consist of 3” 18 Gage Deck with 2 ½” LW concrete slab for a total thickness of 5 ½”. The architect has requested to install ½” ID radiant piping in the floor system. I am not sure exactly what the spacing of these pipes are, but after doing a little research, it appears to be 8”-12” OC. We will eventually receive the actual drawings from the manufacturer, but at this point we do not have it. My initial thought was to reduce the concrete thickness by the thickness of the piping and check the capacity. So a 5 ½” slab thickness has a super imposed capacity of 143 PSF, a 5” slab has super imposed capacity of 133 PSF, a 4 ¾” slab has super imposed capacity of 124 PSF, and a 4 ½” slab has super imposed capacity of 114 PSF. These values are for a 12 foot span and I need to achieve a load capacity of 100 PSF. I believe I am going to be fine based on the capacity with the reduced slab thicknesses. I also saw online that ASCE 3-91 may have some guidance for this but we do not have that document. I may be able to check it out at the NCSU library.

I think ACI says conduit within the slab should be spaced at 3 diameters minimum. It also says that they not be larger in diameter than 1/3 the overall thickness of the slab (lets say 2 ½” slab x 1/3 = .8333” approximately 3/4”-7/8” thickness). It also says to provide a minimum of .002 x area of concrete normal to the piping. In this case we have 2.5” of concrete above the flute x 12” width = .06 in^2/ft. We currently have 6x6 – W1.4xW1.4 WWF in the slab which is .028 in^2/ft. We would need to increase to 4x4 – W2.0xW2.0 WWF to get .06 in^2/ft.

Does this sound reasonable? Would like to hear thoughts/opinions from others.

Thanks in advance!

 

[msquared48]

My initial reaction is that it is OK, but I do have some thoughts here:

If the deck is composite, and you are using the section as composite with steel beams, I would check with AISC to make sure that the effective section modulus does not need to be reduced. Also, considering long term deflection and creep, make sure these are not an issue.

What materials is the Arch using for the piping? What happens when the power goes out and the temperature goes down? Better allow some adjustment for temperature fluctuations. Leaks will be difficult to fix and a financial liability.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask