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RE: Rigid vs. Flexible Diaphragm

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Bill, 
If I interpret you correctly, I think I agree. The 20% paintbrush is a
penalty imposed to force builders to do it correctly by over-designing
the capacity of the materials in case they do it wrong. This is counter
productive as it results in additional cost to the home buyer (owner).
We should be focusing on improving the skills of the framer rather than
arbitrarily increasing the capacity of the materials (or inflating the
demand on the structure).

IMO it would seem that the structural engineering community feels it is
up against a brick wall when dealing with the Building Industry
Association in imposing better skills on framers and even on the idea of
certifying framers to be practitioners and responsible for the work they
produce. It is one thing to follow our details, but another to
over-nail, over-drill hole sizes, place connections too close to the
edge of wood, use 3/8" plywood for its cost, but not pay attention to
crushing plies, not using sill plate kickers when measuring and drilling
for anchor bolts, modifying or damaging truss chords by scabbing on
ceiling accoutrements like lighting soffit (and doing so in construction
without considering the dead load in the original truss analysis and
much more. 

One of the most common issues I have had is that a General Contractor
can obtain his license without the knowledge or ability to interpret or
understand a detail or wall section. The licensing is interested in the
legal and business end of the practice and GC's rely upon a framer's
ability and most framers have little ability unless they worked their
way up in a Union where they received some formal training. NAHB
preaches about their programs that many large developers are using to
train Framers and other trades, but the fact is that only a few of the
thousands who do the work ever get to attend these classes and if they
do, the can be elevated to supervision positions leaving the uneducated
"grunt" to do the labor.

I might sound overly critical, but your point appears to be the
penalization of the one paying the bills because somebody lacks the
ability to do a decent job. We are focusing on the wrong issues and each
time the cost to repair damage increases with inflation, the codes will
compensate rather than attack the real problem - the laborer. 

Dennis


Dennis S. Wish, PE


California Professional Engineer

Structural Engineering Consultant

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

http://www.structuralist.net

 


-----Original Message-----
From: Bill Allen [mailto:T.W.Allen(--nospam--at)cox.net] 
Sent: Monday, April 19, 2004 8:48 PM
To: seaint(--nospam--at)seaint.org
Subject: RE: Rigid vs. Flexible Diaphragm

I'm aware of the LA City approach (the Bay Area [TriChapter] has adopted
it
as well), but why surcharge the "weak/soft" line? The greater load on a
"weak/soft" line will be based on tributary area, i.e, FDA, so why add
anymore load to that line?

Allowing an option to RDA is an improvement, but penalizing the "weak"
line
by 20% is still excessive <insert obligatory "IMHO" here> when a RDA/FDA
envelope would show, and which *most* critical thinking, rational
engineers
would agree based on observation of the model alone, that the maximum
load
on the "weak" line is obtained from the FDA approach.

I believe that the 20% broadbrush approach is good, but only when it's
not
obvious.

T. William (Bill) Allen, S.E. (CA #2607)
ALLEN DESIGNS (http://www.AllenDesigns.com)
San Juan Capistrano, CA

:-----Original Message-----
:From: Stanley E Scholl [mailto:sscholl2(--nospam--at)juno.com]
:Sent: Monday, April 19, 2004 7:49 PM
:To: seaint(--nospam--at)seaint.org
:Subject: Re: Rigid vs. Flexible Diaphragm
:
:well said, Dennis. Too bad that a few building officials continue to
try
:to require rigid analysis for everything. I like the LA City approach.
:They allow flexible analysis but require us to add 20% surcharge to the
:values obtained.
:
:Stan Scholl, P.E.
:Laguna Beach, CA



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