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RE: UBC 1633.2.4

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I have not followed this thread closely. However, half the weight of the
wall is included in the story shear at the roof (base shear for one story
bldg). Therefore, the diaphragm deflection already includes the seismic
movement due to the weight of the wall. I would argue that you should not
have to double up on the seismic weight of the wall.


-----Original Message-----
From: Gerard Madden, SE [mailto:gmadden(--nospam--at)attbi.com]
Sent: Wednesday, April 02, 2003 11:40 AM
To: seaint(--nospam--at)seaint.org
Subject: RE: UBC 1633.2.4


Good,

I read the section of the code 1633.2.4.

If you are considering this as an element NOT part of the lateral
resisting system because the greatest diaphragm deflection will occur
with out of plane loads, it says use the greater of Delta M or Pdelta.
Both factor up Delta S to get Delta M - Delta S is obtained using the
Base Shear not Fp.

If you are considering it as PART of the lateral system (because it's a
shear wall), it specifically says diaphragm deflections shall be
considered and that the flexural and shear stiffness shall not exceed
1/2 gross properties unless a detailed analysis is performed. Again,
diaphragm deflection is not obtained from Fp forces. Compare the out of
plane moment in the panel due to this compared to the mid-height value
in the slender wall design.

I don't think it is the intent to combine both effects simultaneously.

-gerard
Santa Clara, CA

-----Original Message-----
From: Chris Roper [mailto:christophermroper(--nospam--at)hotmail.com] 
Sent: Wednesday, April 02, 2003 11:02 AM
To: seaint(--nospam--at)seaint.org
Subject: RE: UBC 1633.2.4

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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