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RE: wood panel wall aspect ratios: shear transfer around openings

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Title: RE: wood panel wall aspect ratios: shear transfer around openings

Chuck:


I have seen a couple of published examples without anchors each side of an opening where inflection points are assumed at the centers of spandrels and moments are summed to figure shear in the spandrels and this produces panel zone behaviour above and below peirs. I agree that this reduces aspect ratios.

What I am proposing is to still have an anchor each side of the opening and still reduce the aspect ratio.  By putting the anchor each side of the opening you are not going to count on the spandrels to resist overturning and consequently the spandrels will not cause "panel zones" in the walls.  I want the portion of the wall above the window to act like a continuation of the roof/floor diaphragm and the portion below to act like a continuation of the foundation and to provide horizontal drag struts in the wall at the top and bottom of the opening.  It seems like a conservative no brainer and this is how the local building department had allowed garage front shear walls to be designed for years but a dark Orwellian cloud has descended over Anchorage.


Respectfully,

Scott M. Haan P.E.
Civil Engineer
Public Works, Engineering Department
Fort Richardson, Alaska
phone: 907-384-3161
e-mail: scott.haan(--nospam--at)richardson.army.mil



-----Original Message-----
From: chuckuc [mailto:chuckuc(--nospam--at)pacbell.net]
Sent: Tuesday, November 26, 2002 9:25 AM
To: seaint(--nospam--at)seaint.org
Subject: Re: wood panel wall aspect ratios: shear transfer around
openings


Scott-
The recent SEAONC wood design seminar included an excellent presentation
on this subject by Doug Thompson.  The analytical method is Ed
Diekmann's and is published in the Fahey/Williamson book. Kelly was sort
of Ed's protégé and is no doubt well versed in the the calculation. The
intent of this method is to provide a rational method for analyzing the
shear flow around an opening in a shearwall with 2 tiedowns( and
coincidentally allows a way around the 2:1 aspect ratio problem for some
walls).

Ben's understanding of the method is incorrect. His suggestion (and
yours) creates a statically indeterminant system in which the relative
deflections of tiedowns, shearpanels, and strapping would determine the
internal load distribution--something well beyond our meager design
capabilities. At low load levels the forces would certainly head for the
stiffest elements--your 2 "extra", interior tiedowns.  Depending on the
wall geometry and relative stiffness these tiedowns could be quickly
overwhelmed. No question about it though, the analysis is a PITA. One of
this days I'll try to do a spreadsheet.

The perforated analysis by Dolan/Sugiyama/BOCA etc. is intended for
unreinforced openings and is now limited to long walls with 4' panels at
each end.
The reason for Ed's analysis is the fact that the shear in the panels
above and below the window can easily exceed the "pier" shear and unless
you do the calc's there is really no way to design the sheathing/nailing
schedule.  That said, I'll bet most engineers just eyeball it unless
they get caught by a plan checker who really knows his stuff.  I
occasionally just use the empirical "perforated shearwall" method and
add some eyeballed strapping above and below the window--quick and safe
(but conservative).
Chuck Utzman, P.E.




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