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Hooked horizontal bars in special shear wall

Hooked horizontal bars in special shear wall

(OP)
I'm trying to determine the reasoning behind why we're required to hook the horizontal bars around the vertical bars in special reinforced shear walls. I've seen this requirement both in ACI 318 and ACI 530 (concrete and cmu) although ACI 318 only requires it if your design shear in the wall is greater than the Acv*lambda*sqrt(fc) and you don't have boundary elements. I'm asking because I have a cmu building in California under construction and the Contractor didn't measure correctly. When he poured the foundation he placed the vertical dowels too close to the inside edge of the cmu block and he can't get the horizontal hook around it. I'm trying to determine a fix and would like to know the reasoning behind the hook to decide on the best solution. Thanks for the help.

RE: Hooked horizontal bars in special shear wall

I believe that the intent is simply to get the horizontal bars convincingly anchored as near as possible to the "chord" elements of the walls, even if there are not explicit boundary elements. I would expect it to be a matter of greater concern in a high seismic application as one could expect anchorage deteriorating spalling of the block at locations of cyclic plastic hinging in the walls.

As a fix, I'd recommend throwing an extra vertical bar in at the end of the wall just for the purpose of anchoring the horizontal bar hooks. I don't believe that there would be any justification for needing a matching footing dowel for the additional bar.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

RE: Hooked horizontal bars in special shear wall

(OP)
That makes sense. ACI 318 says we still need to provide hooks albeit not around the vertical bars if we have boundary elements. We can also forgo the hooks if the boundary element length is long enough to develop the bars. Looking at that and what you say it appears if we have boundary elements we essentially have a concrete 'core' similar to a column that won't fall apart under extreme loads. So basically all we need is a standard hook or the development length for the horizontal bars in that case. If we don't have a boundary element then in order to make sure the bars are fully developed we have to hook it around the vertical bars.

For my project, I was going to have the Contractor create a boundary element with #3 ties (it's a 12" cmu block so there's plenty of space) but it seems your solution might be easier/cheaper. Thanks!

RE: Hooked horizontal bars in special shear wall

Are the dowels full height? You should have the contractor bend the dowels over at 1 to 6, see ACI 530 specification 3.4 B.11(d).

The hooking of the horizontal reinforcing properly develops loads into horizontal reinforcing and provides additional strength to jamb from the loading and unloading. Did you design your wall as part of chapter 3 of ACI 530? Adding a boundary element at the end of a wall has more of an impact than just adding ties.

RE: Hooked horizontal bars in special shear wall

(OP)
Thanks sandman21, I didn't know about that section in the specs. The dowels aren't full height so they could bend those and still place the vertical bars slightly offset. That also could be a good solution and reminds me about something. The wall is a 12" wall with reinforcement on each face. If the dowel on one side is too close to the cmu block then I wonder if the other dowel is farther away? I'll need to check with the Contractor as this will reduce the depth of the rebar. I should probably go back and check it to make sure it's OK if that's the case although it probably is. And yes I did design using chapter 3.

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