Wire Mesh over Radiant Heat Pex Pipe on Metal Deck 2

[cubexco]

Hello,
I have a 60'x35' 1.5" composite metal deck slab on which we have screwed 5/8" PEX pipes for Radiant Heating.
The decking is supported on approx 18' steel bar joists 4' O.C. The Joists bear on 15' girders.
A 6"x6" WWF is placed over the pipes. The mesh is clipped/screwed to the deck at various overlap joints to prevent it from bucking up too high.
The slab thickness is 4", which would place the mesh at 1"-1.5" under the slab surface.

The County Bldg Inspector refused to allow this, stating that the mesh cannot be over the pipe or cannot touch it.
I showed him a fax from the PEX manufacturer stating that this configuration was acceptable. He wants me to obtain a sealed letter from the EOR stating this configuration is ok.

I have 2 questions:
1. Putting the mesh under the pipe means the mesh would be 2.5" below the surface, Wouldn't that negate the purpose of the mesh?
2. Should I have the contractor cut control joints on this slab?

Thanks!
Nik

 

[Ron]

Q1- No. The purpose of the mesh is to hold cracks together, not to prevent flexural cracking, so anywhere near mid-depth of the slab is OK.

Q2- Yes. Cut the joints at the column lines and equally spaced in between at no more than 10 feet in any direction, and at a length/width ratio of no more than 1.2:1

GET THE EOR INVOLVED IN BOTH DECISIONS

 

[Taro]

Let me play Devil's advocate.

Q1 - Yes. The closer to the reinforcing is to the surface of the concrete, the more effective it will be in holding cracks tight. Although the mesh is not sized for flexural strength, if appearance is an issue at all you would want the reinforcing near the surface where the cracking is visible. The effectiveness of the mesh is questionable if it is laying directly on top of the deck.

Q2 - No. Cutting control joints in a composite slab on metal deck is usually a waste of time. The concrete is mechanically bonded to the metal deck and is not free to contract to the joints that have been cut. I have seen many composite slabs with control joints cut in them that have cracked a foot away from the joints. If crack control is important, additional reinforcing located near the surface of the slab is a better investment than cutting joints.

I second the motion to have the EOR make the call. Be sure that the reduction in slab strength due to the presence of the piping is accounted for.