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RE: Perforated shear wall design

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It's fine to use a methodology that is developed, but this method has
not been tested other than on a shake table which is controlled. I don't
believe in the method in real world as there are too many unknowns that
we discover with each earthquake (Northridge in particular). When I
first heard of this, there was a concern by Richard Cantwell of the
NAHB-RC at the time for how to anchor corners so that the posts
(built-up) were anchored in each plane. Tests were not encouraging. 
While I know that this was the child of the AWC, I have doubts since the
methodology was originally intended and developed within lower risk
zones.
It is easier (albeit more expensive) to provide traditional Holddowns
and distribute load uniformly to each length of wall. Code does not
allow stiffness distribution to wood shearwalls and from my experience
with prior UBC codes, the performance of the home is adequate if the
engineer insures that details are adhered to and comply with the
engineers design.
I don't think that this is an issue of will it work or not. Since the
development of the methodology, there have been no real tests of the
methodology - only controlled performances on a shake table. Remember
that these tests are very controlled (nails not over nailed, straps
properly in place, Holddowns properly installed and holes not
oversized). My point is that give ideal conditions, older codes would be
adequate as they have withstood the test of time. Perforated shearwalls
have not. If used in lieu of conventional construction standards, then I
would admit it would be an improvement, but for engineered design, this
is one engineer who would rather install a Hardy Panel or cantilevered
column in place of a perforated wall.
What do we really save - a $1,000.00 or less on a home that is priced
from $80,000.00 to $400,000.00? Don't we owe it to the home owner - even
at the expense of questioning the developers right of free enterprise -
to represent the safety of those who occupy the building. Finally, the
chance is that these buildings won't collapse as is the case with
conventional construction, but the bottom line is who can afford to pay
the price of repair if the owners out-of-pocket requirement is 15% of
the replacement cost of the building (10% if the deductible is higher
according to the new state plan offer I just received).
Even though I have complete confidence in the home I designed and live
in, I have insurance and believe that if my cost of repair is less than
my deductible, I have something to brag about even though it means a
second mortgage.
Design for performance and protect those who occupy the residence. Don't
be caught by the demands of the developer it is not worth the loss of
peace of mind. There are families at stake and the damage to your home
is no unlike rape - you don't feel safe in the only security that you
thought you had.

Dennis S. Wish, PE

-----Original Message-----
From: Schwan, Martin K. [mailto:SchwanMK(--nospam--at)ci.anchorage.ak.us] 
Sent: Tuesday, December 02, 2003 2:10 PM
To: seaint(--nospam--at)seaint.org
Subject: RE: Perforated shear wall design

The tension chord force is calculated at each end of the perforated
shear wall (T = Vh/[Co x sum Li]) NOTE I FORGOT h in my earlier
post...sorry.  Compression chord force is provided at each end of each
perforated shear wall segment.  C = Vh/[Co x sum Li]


-----Original Message-----
From: Roberto salinas [mailto:salinas_roby(--nospam--at)hotmail.com] 
Sent: Tuesday, December 02, 2003 12:35 PM
To: seaint(--nospam--at)seaint.org
Subject: RE: Perforated shear wall design

Do i need to consider the tension and compression on each of the
internal 
segments that make up the total full height sheething (SUM Li). or just
the 
ends?


>From: "Schwan, Martin K." <SchwanMK(--nospam--at)ci.anchorage.ak.us>
>Reply-To: <seaint(--nospam--at)seaint.org>
>To: <seaint(--nospam--at)seaint.org>
>Subject: RE: Perforated shear wall design
>Date: Tue, 2 Dec 2003 12:21:14 -0900
>
>You must consider what are the tension and compression forces.  Each
end
>of each perforated shear wall segment shall be designed for a
>compression force = tension force.  The compression chord force at the
>end of each perforated shear wall segment is T = C = Vh/[Co x sum Li],
>Where Co = shear resistance adjustment factor and sum Li = sum of the
>widths of perforated shear wall segments (full height sheathing).
>
>-----Original Message-----
>From: Roberto salinas [mailto:salinas_roby(--nospam--at)hotmail.com]
>Sent: Tuesday, December 02, 2003 11:48 AM
>To: seaint(--nospam--at)seaint.org
>Subject: Perforated shearwall design
>
>I have a perforated shearwall question see if some one can help me out.
>If
>i design a perforated shearwall instead of two standard shear wall
>separated
>by a window, i only need to provide hold-downs at both ends.  My
>question
>is, in designing the supporing Element(Beam), do i still consider the
>tension and compression forces at the ends of the oppening in the
middle
>of
>my shear wall or just the forces at the ends of the perforated shear
>wall?
>
>Roberto Salinas, PE
>San Jose, CA
>
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