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RE: UBC 1633.2.4

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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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