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Re: seaint Digest for 23 Sep 2008
- To: seaint(--nospam--at)seaint.org
- Subject: Re: seaint Digest for 23 Sep 2008
- From: joshp(--nospam--at)risatech.com
- Date: Wed, 24 Sep 2008 08:58:40 +0000
- Sensitivity: Normal
At the last NASCC show, I did a short presentation on the Analysis requirements of the IBC 2006 and part of that focused on the Panel Zone Shear deformation requirement of ASCE 7 that you mentioned. That presentation, I believe, is still up on the Support - Technical Papers section of our website.
There is a long and painfully response to that issue. The long explanation is essentially:
1) I don't have the code with me (I'm in Hawaii at the SEAOC conference), but I believe the code reference is specifically referring to "contribution to story drift". That can be interpreted to mean that it only affect building seperation requirements rather than member capacity analysis.
2) The commentary to the FEMA 450 / NEHRP document (which forms the basis of ASCE's Seismic requirements) specifically says that if you use centerline modeling (which virtually everyone does), then you can ignore the effect of panel zone shear deformation.
3) There's also some commentary to AISC 341-05 that says something similar to the NEHRP commentary.
4) Personally, I think this is one of the most poorly written portions of the ASCE document and I can't understand why it wasn't removed years ago.
The painfully long explanation would go into discussions of:
5) Methods to include the elastic effects of panel zone shear deformations.
6) Whether or not this code requirement is trying to address elastic or plastic effects of panel zone shear deformations.
7) How this got added into the code and how difficult it can be to remove or edit even the most poorly written portions of the code.
8) How most engineers seem to be conveniently ignoring this portion of the code.
9) Some even more painful new requirements to AISC's Chapter J (or K) related to panel zone shear deformation which seem to require a non-linear push-over type of analysis.
10) How the above new requirement was moved from the seismic detailing spec to the regular AISC spec and how it now can technically be applied to wind loaded structures as well.
11) How above new AISC requirements will force virtually all engineers to use a more conservative equation for panel zone capacities.
Josh Plummer, SE
From: "Joseph R. Grill" <jrgrill(--nospam--at)cableone.net>
Subject: Panel zone Deformations
This is a multipart message in MIME format.
I have been doing a bit of study trying to get back into some seismic design
after practicing in a location and projects that don't get into seismic
design very deep. Basically residential work in low SD Categories.
Section 12.7.3(b) in ASCE 7-05 requires panel zone deformations to be
included in drift calculations. I've searched through all the resources
that I have, and I can't find an example or even an explanation as to how
this is taken into account. I'm interested in a "long hand" explanation,
but also, how is this included in drift results in software such as Risa2d
If my memory is correct, and it may not be, many years ago I heard that a
percentage increase of the calculated drift without the deformations could
be used. It seems I also recall that if your model is such that member
lengths are taken to center line of the member intersections rather that at,
say, the face of columns, that you are in effect taking the panel zone
deformations into account.
If anyone out there on the list can help me out here, I would appreciate it.