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Dowel Wall to Foundation in SDC D

Dowel Wall to Foundation in SDC D

Dowel Wall to Foundation in SDC D

This question is for a 1-story building, akin to a residential structure.

We have a concrete wall (used for bearing and shear) which changed sizes between the time the footings were poured and when the final documents were released. For the purposes of this question, assume it went from a 14" wall with rebar on both faces to a 10" wall with rebar on both faces. The alignment of one face is maintained, so the other face simply moves in by 4".

The building is located in Seismic Design Category D, which makes us subject to chapter 21 of the 2011 ACI 318. Section stipulates the following: — Longitudinal reinforcement of columns and
structural walls resisting forces induced by earthquake
effects shall extend into the footing, mat, or pile cap, and
shall be fully developed for tension at the interface.

This indicates to us that if we wish to add a new row of reinforcement at the face of the wall that shifted, it would need to be fully developed in the footing. For the dowels that were cast-in, we provided a standard hook. We are using #4's but even at this size of bar, I do not believe we can achieve full development for tension in a 12" footing with 3" of clear cover.

Any ideas on how to detail this transition?

Any ideas on code exceptions that would allow us to develop rebar only for the strength required, rather than for full strength?

I appreciate any help you all can provide.

RE: Dowel Wall to Foundation in SDC D

I don’t have ACI with me but I would look for wording that limits the req’d force to the maximum load that can he delivered by the system. Have you checked the #4 won’t work? Epoxy systems are an option but there are add’l reductions for strength (brittle failure safety factor) when using them in seismic if you can’t develop the anchor.

RE: Dowel Wall to Foundation in SDC D

None that I'm aware of outside of going to a more performance-based design. If they're intended to yield as vertical bars in shear walls typically are, then they'd need to be developed to preclude pull/break out prior to yielding. If they don't, the R factor you've based your entire design on isn't real.

If epoxy doesn't work, maybe could try coring a hole and putting in a #4 dowel with a headed terminator? Think development length for that is less than 9" with a #4 bar so could maybe even go shorter to help avoid coring through the foundation mat. Main worry would be just pulling the plug out from the rest of the footing, but could maybe counter that with a non-shrink grout and bonding agent. Could also do a quick pull test to confirm it can develop yield if you can find someone with a rig that can handle it.

Edit: Would also get the actual concrete strength test results and use real strength for all of this. You have to use the minimum specified in normal design since you don't know what it'll come out to yet. Now that you know what it is, I'd absolutely use it.

RE: Dowel Wall to Foundation in SDC D

Thanks for the responses. I'm curious - is there anything that would preclude us from using a non-contact lap splice between the existing dowels and the new bars in the shear wall? My understanding is that non-contact lap splice is really no different than when they are tied together, but it just doesn't feel like you're getting the same capacity.

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