Shear Core Modeling

[jbjones2001]

I have a question in modeling concrete shear walls configured in a tube, like that found around a stair or elevator. My question is related to a possible difference in how the building should be modeled to calculate drift, and how it should be modeled to design the walls to ACI.

ACI chapter 21, limits the effective flange width of a shear wall to 1/4 the wall height. If I use this criteria the "flange" of the tube is not fully effective, thus the structure should not be modeled as a tube, but two "C" shaped sections.

The question arises in that Two "C" shaped sections potentiall have far less moment of interia than the tube section, depending on how much of the tube flange is effective in the "C's".

So should the building be modeled assuming tube behavior, or "flanged" behavior for calculating drift?

It appears evident by ACI that it should be modeled using "flanged" behavior.

 

[WillisV]

The wall should be MODELED for drift just as it is built - as a tube. Also sure to use the appropriate cracked moment of inertia for the wall when checking drifts.

The wall should be DESIGNED for the effective flange widths per ACI (i.e. as the C-shaped sections) by using only these portions of the wall to resist the forces in the entire tube.

Note that the ACI chapter defines the effective flange width as 1/4 of the TOTAL wall height - not the floor to floor height so unless you have a very short building with a very large core, more than likely you are going to be able to design it as the full tube.