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RE: Boundary elements in shearwalls

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The only place that the boundary elements are required is in 21.6 and 21.7. You are in an "ordinary" concrete wall. You have already taken a penalty in your R value to use the "ordinary" wall as opposed to the "special" wall. You have no code induced obligation to use a boundary element.

The details, including the boundary element, are intended to make the "special" wall more ductile in the nonlinear range. By using the lower R factor, you are requiring your wall to have a more linear response. Even if your stresses exceed 0.2f'c, you are not obligated by the code to use a boundary element.

With all of that, I might still be incliined to add boundary elements to give better structural performance especially if I can keep the boundary elements inside the planes of the wall. It is just a few added sticks of rebar.

There are many places where you can ignore special seismic detailing if you drop your R value low enough. And that is an appropriate thing for the codes to do.

Harold Sprague

From: "Will H" <haynewp(--nospam--at)>
Reply-To: <seaint(--nospam--at)>
To: seaint(--nospam--at)
Subject: Boundary elements in shearwalls
Date: Wed, 18 Aug 2004 17:06:39 -0400

According to ACI 99-21.6.6 the requirements for boundary elements are in reference to "special reinforced concrete walls". I am in SDC C and am using ordinary reinforced concrete walls as allowed by IBC table 1617.6.

Does this mean that I can ignore the need for boundary elements since I am not designing a "special" wall, even if my factored forces exceed 0.2f'c? It doesn't really seem correct to ignore them.


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