Tilt Panel Slab Tie Back Capacity

[Boiler106]

Eastern US: we're seeing tilt panels from many different engineers being restrained with a 15' long pour back strip that is reinforced and tied into an 15' long unreinforced slab on grade panel with a deformed dowel, say 48 inches long, to seemingly utilize the friction force from that slab panel.

Our review shows that the unreinforced panels would certainly still have tension in them, even using a 0.5 friction factor. Reading through ACI plain concrete, this doesn't seem permissible.

We're using at rest earth pressure of, say, 60 pcf and wind on the wall face and ibc lrfd combinations.

Are we missing something in ACI? Should we be using φ5λ√f'c for tension in the unreinforced slab for axial tension in the panel and call it a day?

 

[JAE]

So the panel is designed to span vertically from footing-to-slab-to-roof?

 

[Boiler106]

yes, three points of support as we see it.

 

[JAE]

If it's life safety issue then I'd be wary of using 5 x sqrt(f'c)....which I think it is.

Can't you just call out some additional reinforcement in the second panel slab (perhaps one-way and less than the first panel)?
Or perhaps use a thickened slab edge at the first panel to create some kind of key?
Or disregard the slab and span the panel from footing to roof?

 

[haynewp]

I'm not sure direct tension is allowed in the Plain Concrete chapter of ACI, the φ5λ√f'c is for bending checks. Section 14.5.3 says you can use tensile strength but the commentary for that section is about tension under flexure. I would usually expect at least WWR in this area anyway that could be used for tension.