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RE: 2003 IRC Brace wall lines

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Joseph,
You have entered the argument that we have had for many years now
related to Prescriptive Conventional Construction and Engineering
Design. If the building passes the tests for regularity then the
building may be prescriptively designed. This is where all compatibility
ends. The following is my interpretation of the cause for the
discontinuity between Conventional Construction and the provisions of
Chapter 16 of the UBC and the subsequent IRC.

The IRC is based on a method of design and construction that is also
part of the Uniform Building Code Section 2320 and dates back over 180
years. In the City of Los Angeles, we called it Type V (five)
construction and the City of L. A. had a prescriptive sheet for platform
and balloon framing that was based on the pages taken from the
Architectural Standards manual.  It is based on the method of framing
that began the day the first sawmill was delivered west of the Rockies
(actually west of the Mississippi) by the new railroads and log homes
were sawn into more economical stick framing that was common on the East
Coast. It is a historic method and has been slightly modified and
preserved by the building industry - not by the engineering community.
However, you must understand that prior to the 1980's the structural
engineering community had very little interest (if any) in single or two
family light-framed residential structures. Labor costs were low as was
real-estate prices.

There has been a dividing line between Architects and Engineers on the
issue of home building. It was not until the cost of repair and
replacement of damaged real estate that the Insurance industry pressured
the engineering community to design stricter building codes but even the
insurance industry could not prevent Architects, the BIA and NAHB from
continuing to use the Conventional construction provisions in areas of
high risk. The politics between organizations had reached a level that
it was easier to raise the bar on light-frame design rather than attack
the problem in construction quality or, as you found out, that
Conventional Construction has been allowed to grow into multi-story
structures with more unusual geometric shapes as long as there is no
irregularity (as defined in the code). With this in mind, conventional
construction has been allowed to exist without control by the
engineering community and as you found out, in most cases it will not
meet the minimum standards of lateral design designated in Chapter 16.

As long as the cost to repair damage was within reasonable limits that
the homeowner and insurance company could tolerate, then nobody
questioned the design of residential structures to prescriptive methods.
In fact, the majority of the $30-billion in damages after Northridge was
the result of prescriptively constructed homes that populated the San
Fernando Valley. The NAHB-Research Center (NAHB-RC) attempted to cover
this up but made a mistake of pointing out that the homes performed
within acceptable standards as no loss of life occurred. However, in the
same document they admit that the majority of homes constructed in the
San Fernando Valley damage by the earthquake was constructed by
prescriptive methods dating back to the 60's and 70's. 

The NAHB intended to create affordable housing and to protect lives with
low cost housing that followed HUD standards. It wasn't expected that
real estate values would rise exponentially, creating a major disaster
for the Federal Government and Private Insurance agencies when the cost
to repair damage on an underinsured home or one that had code upgrade
became much more than was planned. 

I remember sitting in on the RRR Committee (Fred Turner will remember
this) - the Residential Retrofit and Repair Committee that was chaired
by Fred for the California Seismic Safety Commission. The members (I was
representing SEAOC when Ben Schmidt could not attend and also as a
private member representing a company that did seismic retrofit of older
homes on cripple walls). It was my impression that the issue of
residential quality of construction was pressured by the Insurance
industry as others at the table represented AIA, the Pest Industry,
Building Officials, SEA, the Insurance Industry and the Building
Industry Association (as well as some who attended and worked in the
field). 

Inasmuch as there were few records of lost lives in even high risk
zones, the quality of construction was deemed adequate and the
structural engineering community rarely was involved in the design of
housing (except the rare high-end custom home)in the majority of the
United States. Retrofit codes were created (but not enforced except
voluntarily) but little was done to bridge the gap between conventional
and full-compliance construction. The NAHB and their tribe was simply
too powerful in government to change their ways. When I tried to discuss
this with one member in power with NAHB-RC, he presented me with skewed
statistics that tried to show that homes performed as expected and that
the cost of repair is the responsibility of those who lived in high risk
areas - it was their cost of living in an area subject to earthquakes,
wind or hurricanes. It was absurd as far as I was concerned for as good
as this man was explaining statistics, his model was based on arbitrary
homes picked in the Northridge earthquakes that were not reported as
damage - he never did a statistical study of damaged homes. What could
we tell about undamaged homes? They were lucky.

The Insurance industry left California and the State set up a private
fund that was taken advantage of by the head of the State Insurance Fund
who resigned and left us to start all over again. The same thing
happened to areas within hurricane regions, and I suppose it will
continue each time an area is affected by tornado's, wind spouts,
termites and pests etc. Sooner or later rather than improving
construction design and quality, we will expect people to afford
engineered homes or live in high risk.

Remember, there are no rules of disclosure for homes that do not mean
the minimum standard of engineered designs. Don't expect the numbers to
balance - in most cases they won't. The public are the people who will
pay the price and they have no idea what they are in store for. 

I know this doesn't help, but maybe you can convince SEA to change their
attitudes toward the design of light-framing and start focusing on
improvement in construction quality and outlawing the use of
prescriptive methods in regions of high risk.


Dennis S. Wish, PE


California Professional Engineer

Structural Engineering Consultant

dennis.wish(--nospam--at)verizon.net

http://www.structuralist.net

 


-----Original Message-----
From: Joseph Grill [mailto:jrgrill(--nospam--at)cableone.net] 
Sent: Monday, April 26, 2004 8:22 PM
To: seaint(--nospam--at)seaint.org
Subject: Re: 2003 IRC Brace wall lines

Martin,

Thanks for your reply.  Once again, I wasn't as clear as I maybe should
have
been.  And, I sent the message from the office between calls etc. etc.
and
just didn't take enough time writing the message (I've got to work on
this
writing thing).  Even with the 8 methods available in the IRC I'm fairly
certain (from the perspective of an arm waive initially looking at the
plans) that I will have some locations where the 8 possibilities won't
work.
That is, if I were to do an actual lateral analysis (per IBC) and try to
compare those requirements with the "working backwards" capacities of
the 8
possibilities from the IRC none of the capacities of the 8 possibilities
would work.  Does that make sense?  I am having a problem with the
prescriptive "allowable" wall types in the IRC as compared with
calculated
loadings from a "full blown" wind analysis (or seismic).  And, I am
fairly
certain from my experience in my new location, that I will be (maybe too
pessimistic) that I will be raked over the coals if I require anything
more
than the prescriptive requirements.  Is there any code provisions for
size,
complexity, layout, etc. that would tell me that the prescriptive wall
types
can not be used, and a full wind (or seismic) analysis is required per
the
code?  If there isn't I'll just have to fight my battle on this one, but
I
was hoping for some code help to explain to the client.  Again, I'm
fairly
new to the IBC, IRC.  Is there such a thing as "code help" with the IBC?
:-)

If that didn't make sense, I'm quitting for the night, going for another
cocktail and my new novel.

Thanks again,

Joseph Grill, PE (Structural)


----- Original Message ----- 
From: "Schwan, Martin K." <SchwanMK(--nospam--at)ci.anchorage.ak.us>
To: <seaint(--nospam--at)seaint.org>
Sent: Monday, April 26, 2004 5:11 PM
Subject: RE: 2003 IRC Brace wall lines


Joe, See table R602.10.1 in the 2003 IRC and sections R602.10-R602.11.3.
There are 8 methods for braced wall panels listed in section R602.10.3.
Table R602.10.1 indicates where the various methods can be used with
respect to seismic design category and level.  I have not gone too far
into this because we are still using the 2000 IRC.  The 2000 IRC had two
braced wall types (see section R603.8); type I is the more traditional
braced wall with no openings and holdowns on each end of each braced
wall.  Type II has openings with holdowns at each end (like the
perforated shear walls).  I do not see the type II in the 2003 IRC,
however.  We use the provisions in chapters 16 and 23 of the IBC.  In
the 2003, check out 2308.9.3 and figure 2308.9.3 for example. HTH


-----Original Message-----
From: Joe Grill [mailto:jgrill(--nospam--at)swiaz.com]
Sent: Monday, April 26, 2004 3:24 PM
To: seaint(--nospam--at)seaint.org
Subject: 2003 IRC Brace wall lines

The area I am working in has adopted the 2003 IBC and IRC.  Are there
any
provisions that tell us where you can not use the Wall Bracing
provisions in
the IRC for lateral?  I am starting to look at the lateral on a
residential
project where the roof diaphragm is pretty broken up with differing
elevations.  I know that I will be asked why the provisions in the IRC
for
wall bracing won't work.  I can't find any provisions myself, but may be
looking in the wrong place.  Also, are there any Q&A materials out there
for
the IRC and in particular the wall bracing provisions?  I have one for
the
IBC.  To me the provisions in the IRC are pretty confusing, and I've
never
had to really look into them.

Thanks,

Joe Grill


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