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RE: [AEC-Residential] Posting of Gary Searer SE Pre-meeting Proposal for changes to Rho

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Thanks for the comments, Jay and I look forward to the publication of the
paper - I would be happy to post any documents that professionals should be
reviewing and be aware of. The main emphasize on the Bulletin Board type
discussion forum has been the ability to make not only the documents
available to professionals but to allow comments and opinions to be posted
as well.

I received an e-mail form Lee Adler, the Executive Director of SEAOC to
advise me that the current Chair of the Seismology Committee is Doug
Hohbach, (dhohbach(--nospam--at)hohbach-lewin.com). He has requested I change the e-mail
link which I will do tonight. Doug Hohbach has authorized Lee to suggest the
comments be sent directly to him. I was hesitant at first to do this because
I did not want to inundate committee member by imposing on his office. FWIW,
we can send responses to Mr. Hohbach.

Although the shearwall system that you describe may have merit, my concerns
are how the perforated wall system will perform when the builder is not
concerned with the quality of the product or understanding of the intention
of the wall as a lateral resisting member. As I mentioned in my post, the
large developer of homes will have more control and will invest in
professionals to insure a good product. They will also invest in training of
their personnel to insure proper installation of materials.

On the other hand, the many of builders and developers of single family
lower and middle income residential homes does not have the resources and,
in most cases in unwilling to invest the time to properly train their
employees. Speaking from specific knowledge of the builders in my area, the
bottom line is profit and in the building boom, time is of the essence.
Builders seek prescriptive methods to maximize their profits. The perforated
wall can help raise the baseline on prescriptive methodology by increasing
the sheathing and performance of the wall as a total system, however, it may
not be effective unless combined with proper training or, in my opinion,
required training (at least of all framers whose job it is to construct a
structural system even if prescriptive).

I would be interested in your comments on these points. Jay, I think you
know that I believe strongly that each side (NAHB / SEA) are diametrically
opposed in ideology and I don't see any wavering.
Regards and thanks for the comments (take a look at the website which has
changed a great deal since you may have looked at it in the past).

Regards,
Dennis S. Wish, PE
The Structuralist Administrator for:
http://www.structuralist.net
AEC-Residential Listservice
admin(--nospam--at)structuralist.net
(208) 361-5447 E-Fax
ICQ # 95561393



-----Original Message-----
From: owner-aec-residential(--nospam--at)polhemus.cc
[mailto:owner-aec-residential(--nospam--at)polhemus.cc]On Behalf Of Jay Crandell
Sent: Wednesday, November 29, 2000 3:08 PM
To: aec-residential(--nospam--at)polhemus.cc
Subject: Re: [AEC-Residential] Posting of Gary Searer SE Pre-meeting
Proposal for changes to Rho


Dennis:

Thanks for keeping the issue of the rho factor in the forefront and
keeping us updated on this interesting example of bad
consequences with good intentions.  I agree that good intentions
do not justify the impacts associated with the rho factor and that
this is indicative of very troubling code development situation.
However, it is not dissimilar to how many laws/codes are made -- it
doesn't actually have to work, it just has to demonstrate good
intention.

On a more upbeat note, we are now getting results from our 3D
system shear wall tests of conventional fully sheathed walls with
corner returns and perforations (openings) as would be found in
actual construction.  The fastenings use pnuematic nails and
conventional construction details with OSB sheathing.  The tested
ultimate capacity of the shear walls (without openings) is about 650
plf (SPF studs at 24"oc, 8d pneumatic nails (0.113" diameter) at
6/12 spacing, 7/16 OSB rated sheathing).  We have found that a
four foot corner return provides sufficient restraint to maintain a
ductile failure mode in sheathing fastners and to realize the full
capacity of the wall as though it were restrained with brackets.
Yet, the walls we are testing are restrained only with anchor bolts
at 6' oc or 16d pnuematic nails (0.131" diameter) per NER 232.
The nails in the sole plate are installed as in the field, some hit the
band joist and some simply penetrate the subfloor without hitting
framing below (50/50 split).   We are finding that the walls exhibit
greater deformation capability (with sustained loads past peak
load) and greater energy dissipation than typical engineered walls,
although this depends somewhat on detailing of the first anchor
bolt connection at the end of the wall line. Although this finding
would likely change for walls that have a greater load demand (and
more sheathing nails) as in supporting multi-family or larger
buildings.  None-the-less, these are very important findings for
typical single family dwelling applications.  We are also finding in
whole building tests that offsets in wall lines (that create internal
corners) have a tendency to actually strengthen the system (not
weaken as alleged in newer codes that have an arbitrary 4' offset
limit).  This agrees with the restraining effect found for corners at
the ends of wall lines.  These findings are conservative in that they
do not include any dead load effect that would further restrain the
walls from overturning.  Our next step will be to create a report on
the test results and then to begin developing a design methodology
that matches this reality.  I hope to share the paper on the
structurallist once it is completed early next year.

Jay
Jay Crandell
NAHB Research Center, Inc.
400 Prince George's Blvd.
Upper Marlboro, MD 20774-8731
301-430-6240
301-430-6184 fax
http://www.nahbrc.org
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