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Was: Tales of Terror #1: NOW: Static vs. Simplified Static analysis

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Stan,
I was planning on getting into a discussion about rational methods (Static,
Simplified Static, Flexible, Rigid, Envelope solutions etc.) at another
time. One thing is certain, not one plan that I have reviewed of the 27
currently in my office uses a rigid diaphragm analysis as the rational
method of design. The real question becomes; What section of the code
explains or differentiates the use of the Static and Simplified Static
methods? I know what subsequent publications have attempted to do (basically
use 3.0CaIW/(1.4R) rather than 2.5CaIW/(1.4R) - this is the 20% difference
you are referring to. I use this as it is my opinion that it is triggered by
the requirements of both methods to check for diaphragm rigidity first. I
know of only one or two instances where the diaphragm is flexible and that
is either with a large cut-out for say an atrium, or where the aspect ratio
of the diaphragm approaches 4:1 (the limits in the UBC). 

I was under the impression that if you use the Static method, you must
design with RDA to find the additional shear that is distributed through the
horizontal diaphragm by rotation due to relative wall stiffness. Although,
most do jump into the Simplified Static design adding the additional 20%, it
seems that the code requires the engineer or architect to first check the
building for irregularities that might exclude the building from the
Simplified approach.

So, what is the standard of professional practice for light-framing that
will protect the professional community against litigation when a seismic
event occurs and the homeowner hires an expert witness who believes that the
letter of the code was not followed and that additional demand in the
diaphragm was the culprit that caused the failure. 

IMHO, I believe these are fairy tails, and NO! I have not gone over to the
dark side (although it looks like fun). I accept the judgment of the owner
of the agency paying me to do the work as what constitutes a minimum level
of compliance to the code and I don't expect others to design as I would. 

I think this has been a sore point with those of us in the professional
community who have never seen the resolution to this issue and are currently
lucky to not have to have the law tested. Should we all agree to one
standard and come in groves to the courthouse to testify in favor of the
poor guy who finds his pot of gold (Insurance) jeopardized?

Sorry to be so cynical, but the term rational method has currently become an
oxymoron.


Dennis S. Wish, PE


California Professional Engineer

Structural Engineering Consultant

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

http://www.structuralist.net

 


-----Original Message-----
From: Stanley E Scholl [mailto:sscholl2(--nospam--at)juno.com] 
Sent: Tuesday, June 29, 2004 10:12 PM
To: seaint(--nospam--at)seaint.org
Subject: Re: Tales of Terror #1: Architects doing engineering


Dennis- as you know, in CA architects and civil engineers are legally
equal- each can design whatever they can find a client to pay them to do
except neither can design a public school or public hospital. The
problems you are finding are not different than when a civil engineer who
is more at home designing water lines or highways tries to design a
building. I use tributary areas in designing distribution to diaphragms
(considering them flexible)  except in Santa Monica where we have to use
the rigid diaphragm procedures- which result in much more design time but
not much difference in shear values. I think LA has the best idea- just
add 20% to demands found in flexible analysis procedures (using tributary
loads).. I have never heard of anyone using what seems to be overly
simplistic (and in error) 1/3, 1/3, 1/3 methods.
I would be interested in seeing tests that show a simple distribution. We
could then use them and save a lot of work.

Stan Scholl, P.E.
Laguna Beach, CA

On Tue, 29 Jun 2004 09:45:07 -0700 chuck utzman <chuckuc(--nospam--at)pacbell.net>
writes:
> Dennis-
> IMHO the dumb architect has it right  & you persist in doing  it 
> wrong :o)
> Every test I'm aware of shows the distribution to be 1/3, 1/3, 1/3. 
> (If  
> it doesn't  change the wall construction, I sometimes use 1/3, 1/2, 
> 1/3 
> just to keep plan checkers like you at bay.)
> 
> At a SEOC convention in S.F. a few years back, researchers from 
> Texas 
> IIRC presented their test results from a simple unblocked pitched 
> roof 
> building.  The uniform load at the top plate distributed itself  
> 1/3, 
> 1/2, 1/3.  Likewise for every reasonably proportioned floor 
> platform.
> 
> Chuck Utzman, P.E.
> 
> Dennis Wish wrote:
> 
> > I started to write this in order to vent my frustration as a 
> contract 
> > (sub-contract) plan checker who has found that more architects are 
> 
> > designing the structural elements of high-end custom homes. This 
> is 
> > upsetting – I’m actually making money as the more errors I find, 
> the 
> > more time I spend and the more I make hourly. I don’t need to 
> design 
> > their homes, I only need to plan check them.
> >
> > Don’t misunderstand, I know a great many architects who became 
> > engineers and they went through the hard work to prove they were 
> > capable. But what I am seeing are architects who think they 
> remember 
> > their statics and strength of materials from forty years ago and 
> > attempt to apply it today in order to save the cost of hiring an 
> > engineer. Three or four plan check cycles later, they tend to find 
> 
> > engineers to help them through the things they don’t understand.
> >
> > Just one example – I can’t resist this one. The designer (I am 
> > hesitant to use the title architect) calculates the base shear of 
> a 
> > fairly rectangular building with three lines of resistance. Rather 
> 
> > than waste the time to design the distribution of the two 
> diaphragms 
> > between the three grid lines as simply supported beams, the 
> architect 
> > applies 1/3 of the total lateral load to each line of shear. Have 
> I 
> > missed something? I’ve been used to figuring the reactions which 
> > almost always ends up with 50% of the shear in the middle wall and 
> 25% 
> > at each end. He would have been better off eliminating the center 
> 
> > shearwall had it not been for a re-entrant corner and don’t get me 
> 
> > started on that one.
> >
> >  
> >
> > What has this world come to when BORPELS (California) has no 
> control 
> > over architects practicing engineering and the office of the 
> > Department of Consumer Affairs that licenses Architects will do 
> > nothing until the damage occurs and the Architect is considered 
> > potentially negligent (I’ve checked – trust me).
> >
> >  
> >
> > Politics has reached every segment of our society – I mention 
> > certification of Framers and find the BIA (Building Industry 
> > Association) putting me on their black list.
> >
> >  
> >
> > So, what’s your take on all of this? Should I just retire to 
> > Southeastern Arizona and become a hermit (with my wife family and 
> dogs)?
> >
> >  
> >
> > Dennis
> >
> >  
> >
> >
> >       Dennis S. Wish, PE
> >
> > California Professional Engineer
> >
> > Structural Engineering Consultant
> >
> > dennis.wish(--nospam--at)verizon.net <mailto:dennis.wish(--nospam--at)verizon.net>
> >
> > http://www.structuralist.net <http://www.structuralist.net/>
> >
> >  
> >
> >
> > ---
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> >
> 
> 
> 
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