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RE: UBC 1633.2.4

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I am using 1914.8, but I think you're wrong. It's my understanding that those P-delta effects are from the center of the panel bowing outward due to out-of-plane Fp forces (panel is pinned top and bottom and the center moves out). I'm talking about the addition of effects from the top of the panel moving in/out relative to the bottom as it moves with the deflecting roof diaphragm. I don't think this is covered in 1914.8.





From: "Gerard Madden, SE" <gmadden(--nospam--at)attbi.com>
Reply-To: <seaint(--nospam--at)seaint.org>
To: <seaint(--nospam--at)seaint.org>
Subject: RE: UBC 1633.2.4
Date: Wed, 2 Apr 2003 10:51:30 -0800

Your are designing for Pdelta effects in your slender wall design (or at
least you should be). That should take care of it. See UBC 1914.8

-gerard
Santa Clara, CA

-----Original Message-----
From: Chris Roper [mailto:christophermroper(--nospam--at)hotmail.com]
Sent: Wednesday, April 02, 2003 10:44 AM
To: seaint(--nospam--at)seaint.org
Subject: RE: UBC 1633.2.4

The wall is being designed to resist flexure due to out-of-plane Fp
loads as
though it were pinned top and bottom, and this makes sense.  It also
makes
sense that the wall is able to resist P-Delta effects when to top of the

wall moves in/out along with the diaphragm as it deflects (in this case
from
the walls perspective it is pinned at the bottom and has a horizontal
roller
or more appropriately a spring at the top which allows the diaphragm
deflection.)  What isn't clear is whether these two effects need to be
COMBINED at the same time.  If out-of-plane loads are to be combined
with
the P-Delta case (at delta m level), it seems to me they should be at a
"base shear" load level rather than the "element" or Fp level since the
delta m diaphragm deflection that we're talking about originates with
delta
s which is based on "base shear" loads.  Using delta m deflection plus
Fp
out-of-plane loads seems to be conservatively adding apples to oranges.
The
code and examples are not clear on the issue.





>From: Michael Bryson <MBryson(--nospam--at)mhpse.com>
>Reply-To: <seaint(--nospam--at)seaint.org>
>To: "'seaint(--nospam--at)seaint.org'" <seaint(--nospam--at)seaint.org>
>Subject: RE: UBC 1633.2.4
>Date: Wed, 2 Apr 2003 09:01:25 -0800
>
>Yes you have to, but if the wall is essentially pinned at both ends
then
>there are negligible forces generated in the wall when the roof
deflection
>is perpendicular to the wall, yes?
>
>-----Original Message-----
>From: Chris Roper [mailto:christophermroper(--nospam--at)hotmail.com]
>Sent: Wednesday, April 02, 2003 7:57 AM
>To: seaint(--nospam--at)seaint.org
>Subject: UBC 1633.2.4
>
>
>The code requires that structural framing elements connected to the
roof be
>designed to resist "expected" horizontal displacements of the roof
>diaphragm
>
>so that it will continue to support dead plus live loads when subjected
to
>these deformations . . . this is a delta m deflection number.  I am
looking
>at the case of an exterior concrete tilt-up panel building with a
flexible
>plywood diaphragm.  Delta m deflections of plywood diaphragms can be
large.
>
>Out-of-plane Fp loads for design of concrete wall panels can also be
large.
>
>Is it the intent of the code that wall panels in this case be designed
for
>out-of-plane Fp design forces AND with forces resulting from a delta M
>displacement of the wall panel at the roof level?  What have other
people
>been doing and how do you interpret this portion?  The SEAOC Seismic
Design
>Manuals which have examples conveniently stop short of providing any
>guidance in their examples.  As usual they lead you to believe that it
is
>appropriate to take every conservative measure possible, all at the
same
>time.
>
>Your input is appreciated.
>
>Chris Roper, PE
>
>
>
>
>
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