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How do I properly support wall panels?

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al2143

Structural
Sep 11, 2021
2
Hello -

I have a CMU shear wall supported on a pile cap running along the length of the wall. I want to determine the reactions at the ends of the panel to design the end zone rebar. I have experimented with:

1) Continuously pinned along the base
2) Continuously pinned along the base AND explicitly pinning the two joints at the ends of the panel
3) Only pinning the joints at the ends of the panel and leaving the base of the panel as a "free" edge

Question - What is the most accurate way to support the wall panel to get this load? #3 makes the most sense - it will give me reactions at the ends of the panel. #1 and #2 gives me a "distributed reaction" along the panel. I'm conflicted because #1 or #2 seem to be the most realistic but I don't know how to get the end zone loading from this distributed reaction.

And a related follow up question - What if I have one long shear wall, say 60 ft long and I modeled it as (3) panels, each 20 ft long? The end zones should be at the ends of the 60' wall. Should I use option #3 but only at the joint at 0 ft and at 60 ft?

Thanks!
 
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I would submesh the wall into smaller sections (1' to 2') and create fixed connections with reactions along the bottom. You can check Von Mies stresses in the wall to make sure that the model is accurate and that you don't have any concentrated stress points (it happens sometimes with submeshed plates). Most connections are not fully pinned or fully fixed, so you have to choose the end condition or boundary condition that is closest to the expected behavior. If you have bars extending into the grouted cells from the pile cap or grade grade beam, it should be capable of supporting a moment at the base.

All of that is under the assumption that I understand what you are trying to do. A sketch is worth a thousand words or something like that.
 
1) Continuously pinned along the base
2) Continuously pinned along the base AND explicitly pinning the two joints at the ends of the panel
3) Only pinning the joints at the ends of the panel and leaving the base of the panel as a "free" edge

Question - What is the most accurate way to support the wall panel to get this load? #3 makes the most sense - it will give me reactions at the ends of the panel. #1 and #2 gives me a "distributed reaction" along the panel. I'm conflicted because #1 or #2 seem to be the most realistic but I don't know how to get the end zone loading from this distributed reaction.

1)Continuously pinned along the base: This is how I would model the wall. It's continuously connected to the pile cap, right? Therefore, the lateral restraint is continuous for sure.

2) Continuously pinned AND boundary conditions at the end joints: I would not do this. The behavior of the model should be exactly the same. But, the way the results are reported would change. It will be more difficult to determine the total shear in the all and the total vertical reaction (or moment) in the wall because some of that information will diverted into the reactions reported at the two joint boundary conditions.

3) Continuous shear restraint along the wall and vertical restraint only at the end joints: Note that this is different than what you suggested. But, if you only have vertical piles at the ends of the wall, then this might be a better way to model it.

The problem I have with your question is you're confusing modeling with design. I want to get the most accurate representation of the stiffness and load distribution in the model. That's why I suggest that #1 is probably best.

Once I have that information, I will have shear, moments and axial force in that wall. I can use those design forces to properly design the wall. For the most part (in my opinion) end zones are really a detailing requirement. We don't need to force the model to behave as if the end zones will take all the force because they really won't. However, we have code requirements for reinforcing that make us treat those end zones differently.... Which we still have to do. But, it's a slightly different concept from how to best model our structure.
 
Thank you Josh Plum & DiBeachDude very much. I will use a continuous support at the base.
 
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