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Pullout Capacity of Embed plate in bottom of DT Stem

Pullout Capacity of Embed plate in bottom of DT Stem

Pullout Capacity of Embed plate in bottom of DT Stem

(OP)
I have an embed plate in the bottom of a existing double tee stem(10DT24). The embed has a couple of 12-inch long #3 D.A.B extending up into the stem. I can't find a method anywhere that says how to calculate the tension capacity. I could look at the concrete breakout failure mode per App D, but I am not 100% sure what the Hef would be. My initial thought is something less than the full 12" length, but App D tells you to use the full embed for an epoxy bar so it doesn't seem unreasonable to use the full 12".

How do others address this?

RE: Pullout Capacity of Embed plate in bottom of DT Stem

I try to give it to someone who works for me.

RE: Pullout Capacity of Embed plate in bottom of DT Stem

(OP)
Slickdeals,

I have no idea who manufactured them, but the bar itself isn't my problem. It is the edge distance issues with the bars installed vertically in the bottom of the stem. What is the breakout shape? You can't just breakout the concrete with a few strand passing through, but the pre-compression from the strand would help flatten out the 1.5:1 App D failure surface.

RE: Pullout Capacity of Embed plate in bottom of DT Stem

Does the #3 meet the development criteria, if so, then isnt it based on tension of the steel?

In other words, if I develop a piece of rebar, I dont have to use AP. D right?

RE: Pullout Capacity of Embed plate in bottom of DT Stem

(OP)
I started off with the same thought ztengguy. It is developed so I am good. But lets say I have a #3 centered in a 1.875" piece of concrete (3/4" cover each side) I don't think the standard development length equation is the controlling limit state. Why can't the concrete just break out as it would for Appendix D?

RE: Pullout Capacity of Embed plate in bottom of DT Stem

I agree with the approach that you've suggested above Dcarr. And I share your frustration that there's not an explicit method available for dealing with this. I also don't believe that developing the rebar alleviates the concrete breakout failure mode. However, we debate that issue here almost weekly.

The greatest trick that bond stress ever pulled was convincing the world it didn't exist.

RE: Pullout Capacity of Embed plate in bottom of DT Stem

A failure would most likely be splitting along the bar, even if fully developed, especially in thin sections or near edges. With the precompression from the PT, and whatever mild reinforcement is present, one could probably use the developed rebar/DBA capacity for tension. If the bars are not in line with/parallel to the tension, the issue might best be assessed by FEA or testing. App D breaks down when you get into complicated, reinforced, and disturbed regions. Complicating this scenario, the PT strands will tend to drive a splitting plane. If the plane is vertical, along the embedded bars, heavily loaded DBAs could promote this splitting - this is one reason I say testing might be needed.

RE: Pullout Capacity of Embed plate in bottom of DT Stem

(OP)
Thanks TX. These are existing DT's in a rather public facility so testing isn't going to happen. The original designers specified the embed plate specifically to hang loads from, but provided no maximum allowable load for the embed. I need something on the order of 4kips (service) and I feel I can get that, but still like to have something to hang my hat on.

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