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RE: Wood Construction Holdowns at Corners

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Gerard-

If you do a proper RDA, your analytical results will show the additional
forces due to the accidental torsion and you won't have to add the
arbitrary 30%. That's why I don't believe the Orthogonal Effects
provision is related to rigid diaphragms. Yes, SRSS is probably more
accurate (and the Code alludes to this fact) but provides the 100% + 30%
option as a conservative, but simpler approach (which I appreciate).

But, I'm glad we agree.

:o)

Regards,

Bill

:-----Original Message-----
:From: Gerard Madden, SE [mailto:gmadden(--nospam--at)attbi.com] 
:Sent: Friday, May 30, 2003 4:25 PM
:To: seaint(--nospam--at)seaint.org
:Subject: RE: Wood Construction Holdowns at Corners
:
:
:If the earthquake comes at an angle that is not perpendicular 
:to the LFRS, you will get less than 100% in each principle 
:direction. However, in RIGID Diaphragm structure, you could 
:get 100% with a head on EQ force and still get a significant 
:load perpendicular to the EQ force due to the eccentricity of 
:the Center of Rigidity and Center of Mass and then accidental 
:torsion and torsional irregularity.
:
:I guess I would say that I don't disagree with you Bill, but I 
:don't think the effect is as great in a flexible diaphragm 
:building. Chapter 16 defines flexible diaphragm if I'm not 
:mistaken, but none-the-less, I agree that the corner post 
:should be checked for both directions and some combo (be it 
:100-30 or SRSS) regardless of the diaphragm classification.
:
:-gerard
:Santa Clara, CA
:
:
: 
:-----Original Message-----
:From: Bill Allen [mailto:T.W.Allen(--nospam--at)cox.net] 
:Sent: Friday, May 30, 2003 6:35 AM
:To: seaint(--nospam--at)seaint.org
:Subject: RE: Wood Construction Holdowns at Corners
:
:Gerard -
:
:I don't agree that this is a rigid diaphragm issue, that's why 
:the Orthogonal Effects requirement is in Chapter 16. 
:
:I think the requirement is to account for the fact that the 
:shock wave will NOT hit the building perfectly aligned with 
:one of the principal axes. For this reason, I believe an 
:Orthogonal Effects check is necessary with structures with a 
:flexible, rigid or semi-rigid diaphragm.
:
:Chris-
:
:I'm not sure I can see the difference between a column common 
:to two perpendicular frames (moment or braced) as opposed to a 
:column common to two perpendicular shear walls. The mechanics 
:are the same. The demand is the same. The Orthogonal Effects 
:requirement should be the same.
:
:Regards,
:
:T. William (Bill) Allen, S.E. (CA #2607)
:V/F (949) 248-8588
:San Juan Capistrano, CA
:
:
::-----Original Message-----
::From: Gerard Madden, SE [mailto:gmadden(--nospam--at)attbi.com] 
::Sent: Thursday, May 29, 2003 11:40 PM
::To: seaint(--nospam--at)seaint.org
::Subject: RE: Wood Construction Holdowns at Corners
::
::
::This gets back to rigid diaphragm argument and a code with 
::broad strokes. If the diaphragm rotates, the orthogonal 
::effects requirement is a valid check. The question remains as 
::to how rigid the wood frame building's diaphragm is to 
::necessitate this check.
::
::As far as how much axial load could a corner post be subjected 
::too, relatively speaking, it could be quite high or close to 
::capacity. Corner doesn't necessarily mean perimeter corner. 
::The OT chord force is the governing axial load, usually not 
::the gravity load.
::
::-gerard
::Santa Clara, CA
::
::-----Original Message-----
::From: Chris Roper [mailto:christophermroper(--nospam--at)hotmail.com] 
::Sent: Thursday, May 29, 2003 6:26 PM
::To: seaint(--nospam--at)seaint.org
::Subject: RE: Wood Construction Holdowns at Corners
::
::I think you guys are off the mark here.  I always thought that 
::this was 
::intended to apply to frame buildings where a column was part 
::of frames in 
::both orthogonal directions.  It seems silly to apply this to a 
::corner post 
::or column in a wood framed structure.  Besides, how much axial 
::load could 
::the corner post or stud be carrying in typical conditions?
::
::
::>From: "Bill Allen" <T.W.Allen(--nospam--at)cox.net>
::>Reply-To: <seaint(--nospam--at)seaint.org>
::>To: <seaint(--nospam--at)seaint.org>
::>Subject: RE: Wood Construction Holdowns at Corners
::>Date: Wed, 28 May 2003 14:12:49 -0700
::>
::>Pat-
::>
::>1997 UBC, section 1633.1
::>
::>Read the paragraph following the exception below "A column of a 
::>structure forms part of two or more intersecting 
::>lateral-force-rresisting systems."
::>
::>Regards,
::>
::>Bill
::>
::>
::>:-----Original Message-----
::>:From: Pat Clark [mailto:bcinc(--nospam--at)nanosecond.com]
::>:Sent: Wednesday, May 28, 2003 10:29 AM
::>:To: seaint(--nospam--at)seaint.org
::>:Subject: Re: Wood Construction Holdowns at Corners
::>:
::>:
::>:Bill, where do you find these factor for combining these hd forces?
::>:
::>:Pat Clark
::>:
::>
::>
::>
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