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Epoxy holdown into existing PT slab

Epoxy holdown into existing PT slab

(OP)
I am doing a small residential remodel where the existing slab is post tensioned. Long story short because the owner wants a new bedroom in an existing 3 car garage I have the following 2 issues related to the existing PT slab:

1. I will have a new wood framed shear wall with 2 new holdowns that will need to be epoxied into the existing exterior perimeter footing.
2. The new 2x stud wall between the new bedroom and the existing garage will be non bearing, but it will have to sit on a new concrete curb. Since this new conc curb will be located in the interior of the existing PT slab I am proposing to dowel 3" min into the existing pt slab w/#3 dowels @ 18" o.c. and form the new curb.

My question is if I state on the plans to have the existing PT slab scanned in order to locate the existing tendons prior to any work, would epoxying new holdowns into that exterior footing be an issue as long as they do not cut a tendon?

Any comments would be greatly appreciated.

Erik Gibbs P.E.



RE: Epoxy holdown into existing PT slab

I doubt they would agree to the scanning, but if they do, that would be great.

I deal with this issue constantly because of omitted/misplaced hold downs. If the hit a tendon, it snaps and they have to re-thread a new one.

The definition of a structural engineer: overdesign by a factor of 1.999, instead of the usual 2.

RE: Epoxy holdown into existing PT slab

GPR is cheap. Require they scan it. I don't see a problem with adding holddowns so long as the slab can handle it.

RE: Epoxy holdown into existing PT slab

I agree.

Mike McCann
MMC Engineering

RE: Epoxy holdown into existing PT slab

The tendons in the majority of post-tensioned foundations are located in the center of the slab and run flat from anchor to anchor. Care should be taken by the contractor and deputy inspector to eliminate localized kinks (vertical and horizontal) in the strands when they extend over footings or where they are curved to avoid penetrations. The strands are intended primarily to provide a precompression force throughout the foundation to reduce flexural tension stresses. They are not designed as tension reinforcement that conforms to the moment diagram as they would in elevated slab and beam design. The design of these foundations is based solely on allowable stresses, so placing the tendons at different locations of the slab will not provide in any benefit in the design.



kansas city concrete companies

RE: Epoxy holdown into existing PT slab

I wanted to elaborate on this thread as well. I was looking around and this is a pretty relevant issue for me at the moment. I'm working on doing a second story extension to a single family home and I'm going to need to add additional load on the perimeter of the existing 12" P.T. slab and epoxy some holdowns to account for uplift. The contractor intends to scan the slab to avoid cutting any tendons - so if I can get away without damaging any tendons, is there anything else I should be cautious of? Also, in "your" (collective) experience, how much of a perforation can I make in the slab for my reference?

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