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Re: Etabs Shearwalls

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I deliberately assigned different panel numbers to the flanges so I could more easily determine internal forces in each piece. We are concerned about vertical stress between flanges and webs along with several other issues. If I assign the flange the same number, I will lose the internal detail. That said, I will go back and renumber the group I am most concerned about and see what that tells me. I strongly suspect the flanges and how I understand the out-put are the problem.

Your comment about using shell instead of membrane elements is interesting. It seems to imply that there may be out-of-plane buckling issues. Is that possible? The way I understand the Etabs documentation, the membrane elements don't contain an out-of-plane stiffness (or degree of freedom) which is considered in the stiffness matrix.

I can't find an explicit definition of what the pier moment, shear, and axial out-put considers. Does it take the corner forces of each plate and sum them only at the top/bottom of the pier? Or does it somehow consider forces on the edge of the pier? My primary concern is the discontinuity in the pier moment diagram. If it sums membrane corner forces, then summing moments at the bottom of the elements above a floor should give exactly the opposite of summing forces at the top of the elements below. Remember there are no vertical loads in my model which could affect the sums.

Thanks for your insight,

Jake Watson, P.E.
Salt Lake Ci

Tim Shannon wrote:

It could be your definition of the pier assignments for the output.  How have you assigned pier numbers to the flanged walls?

Also, have you tried modelling the walls as shell elements - especially if you are meshing the walls they will likely require out of plane stiffness unless all of your nodes meet perfectly with the floor levels (ie no holes in walls or coupling beams etc) - I usually find it beneficial to use shell elements for walls for this reason.
I could take a look at the model if you want.

Tim Shannon (MIEAust)

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