Bonding (2) slabs in high wind zone

[BubbaJ]

I have a project where there is an anticipated 170 psf suction force on a roof topping slab. The purpose of the slab is to protect the roofing below it. #3 ties were provided in a 6'x5' grid to anchor the slab to the precast double tee roof structure.

A series of unfortunate events for the contractor has resulted in a slab w/o the required reinforcing and the wrong fiber additive.

In lieu of tearing the slab off and starting over, the contractor has come up with the attached detail. They want to drill in new #3 "within an inch or two" of the existing #3. If the two slabs are adequately tied together, the resulting factored suction force is 118 psf or 3540# of hold-down force required per exist #3 tie.

I can't see how there will be adequate force transfer from the new #3 to the existing #3 to prevent the topping slab from becoming airborne during a 300 mph wind event.

Opinions anyone? (We can't drill new anchors into the dbl tees as we don't want to perf the vapor barrier that is below the insulation.)

 

[shin25]

What are you concerned about, is 3540 lbs per #3 existing bars are too high. This is about 31 ksi per bar, which does not seem too high. I am expecting that the very top slab is not yet cast?

Depending on the type of bonding agent used, bonding agent itself can transfer 170 psf of uplift without any problem to the slab below. #3 bars on top of the bonding agent is just over kill. Try looking into SIKA ARMATEC-110 EPOCEM.

Prescribe, roughened interface and SIKA armatec and you should be good to go. Assuming that you have enough reinforcing to transfer the force to DT.

 

[JAE]

Don't you need 6" to develop a #3 hook? (see ACI 12.5)

Doesn't look like you can get that here. The hooks would simply pull out of the concrete given enough load.

 

[BubbaJ]

Thanks for the lead. I contacted Sika and they suggested Sikadur 32 Himod in lieu of the Armatec 110. Do you have experience with that product?

I wasn't concerned about the #3 tensile force being too high. I was concerned about the reality of the force transfer path from the new #3 to the existing #3.

 

[shin25]

I mostly have experience with Armatec as bonding agent. We usually prescribe it because it has a long gel time. Which comes in handy if the contractor encounters delay while pouring. Any way, while selecting, try to compare the properties of both the agents. Why SIKA recommended 32?

 

[UcfSE]

I agree with JAE about the hooks. It won't matter what your fix is if you violate another part of the code and nullify your solution.