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# Re: Etabs Shearwalls

• To: <seaint(--nospam--at)seaint.org>
• Subject: Re: Etabs Shearwalls
• From: "Tim Shannon" <tim(--nospam--at)nsw.meinhardt.com.au>
• Date: Thu, 20 Apr 2006 10:21:57 +1000

```Jake

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)

>>> jwatson(--nospam--at)utahisp.com  >>>
We are modeling some very convoluted shear walls in Etabs and trying to
check the model by hand.  Walls in the model without any flanges behave
as anticipated: continuous moment diagrams, forces above and below floor
lines match, shear diagrams increasing / decreasing as appropriate.  Our
walls with flanges have "jumps" in the wall moment diagrams.  The moment
above a floor will be one number (say 1000 ft-k) and below the floor it
might be be 500 ft-k.  These points are the bottom of wall panel and the
top of the panel below.  My hand calc of P/A +/- Mc/I to check wall
stress in an individual panel gives substantially different results.
Meanwhile the Etabs panel plate corner stress plots are realistic and
continuous.  Can anyone explain what Etabs is telling me?

A few model notes:
We didn't model any gravity or "self-weight".  I like to check this
stuff by hand.
All walls are "membrane" elements, no out-of-plane stiffness
The diaphragm is modeled as infinitely rigid (we didn't mesh it and have
turned off that "feature").
I have hand meshed the walls to get appropriate element size and shape
(this is not my problem, I have a fair amount of experience with FEA meshes)

Jake Watson, P.E.
Salt Lake City, UT

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