# FEA Member offsets and Panel Zone Deformation



## McEngr (Jan 23, 2012)

Rafael Sabelli brought up an excellent point about drift and panel zone deformation in the Kaplan review course. He basically said that if the member to member connections to the nodes are from center-to-center of say a special moment frame of steel, that the panel zone deformation can be ignored. I thought I would share this insight as I have been wondering how to account for this on the exam (seeing as how AISC 341 does not address it explicitly).


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## McEngr (Jan 23, 2012)

I could see of some exceptions to this rule, but Sabelli was making a rough generalization and stated this in his presentation.


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## ipswitch (Jan 23, 2012)

As is "zero force member?"


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## McEngr (Jan 23, 2012)

If you were, for instance, going to design your beam from the face of column and have an "inactive" member in risa merely to transfer the force, you would have to account for the deformation. However, if you go from center line of column to center line of beam, one could make this conservative assumption to neglect panel zone deformation in most cases.

I assume you've used RISA, or eTABS or STAAD?


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## ipswitch (Jan 23, 2012)

I've used STAAD quite a bit. I haven't used RISA since college. I sorta don't know what you're talking about. I'd have to read up on this stuff.


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## McEngr (Jan 23, 2012)

Sorry ip. The issue is pretty simple - so I'm not doing a great job of explaining it evidently. If you design your members without consideration of offsetting the dimensions for the actual clear span dimension of the members, the deformation is still being designed.

Like for a portal frame with a lateral load at the top (bridge engineers call this a "bent" I think), then your beam would be long because it isn't modeled from face of column to face of column. Does this make sense?

Potentially for the SE, this could be an "interpret analysis program" problem.


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