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Re: IBC 2007 Wind calcs.

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Several years ago, when the 2003 IBC was starting to be accepted around here I went to a seminar put out by ASCE, I believe. Due to the large amount of information and the complexity of the methods, and being entirely new to most all of the participants, I didn't walk away with much of an understanding of the methods. Of course, as always, any examples done in the seminar were pretty simplistic as compared to what many of us do in practice. However, one of the things I do remember from that painful experience is this. One of the people attending ask when the "Simplified Method" could and could not be used and how much of a variation from the figure there could be before the "Simplified Method" could not be used. My understanding of the reply was that very little variation from the figure would push the method to the analytical method. The "Simplified Method" resulted from testing done, if I remember correctly, in conjunction with, or maybe it was done by, the PEMB industry. Any projections, more than a few feet, from the shape in the figure would make the structure non-symmetrical, which is one of the criteria to use the "Simplified Method". Therefore, my understanding was that there wasn't a lot of structures that could use the "Simplified Method" except those that looked pretty much like that in the figure.

I would like to attend the same seminar now that I am a bit more familiar with the whole nightmare, and since things have now moved on to the ASCE 7-05 version.

Joe


----- Original Message ----- From: <William.Sherman(--nospam--at)CH2M.com>
To: <seaint(--nospam--at)seaint.org>
Sent: Sunday, February 17, 2008 1:00 PM
Subject: RE: IBC 2007 Wind calcs.


Last year, ASCE/SEI ran Trial Design Problem 01-06 that included
submissions of wind and seismic forces for a simple box building.  These
trial design problems are intended to test application of code
provisions by practicing engineers.  (It includes some discussion of
application of the 10 psf minimum wind pressure.)  A "White Paper"
summarizing the trial design results can be found at:
http://content.seinstitute.org/committees/business.html

As with past trial problems, there were significant variations in the 54
solutions submitted by practicing engineers.  Some engineers chose the
simplified wind provisions from ASCE 7-05 and some chose to use the
analytical procedure.  The White Paper notes that results were much more
consistent among those that used the simplified procedure; but "The
Analytical Method (Method 2) is not clearly understood or consistency
applied as demonstrated by the large variation in the design wind
pressure."

Personally, I find the analytical wind provisions "too complex" with
respect to the time and effort needed to apply them vs the benefits
derived.  But the trial design problem identifies another significant
problem with the complexity - it actually increases the incidence of
errors in applying the code provisions.

Another conclusion that can be reached from the trial design problem is
that an engineer's calculation for development of building loads from
code provisions should be checked by another qualified engineer.  It is
likely that an independent set of eyes and a different viewpoint in code
interpretation would reduce the incidence of errors in derived design
loads.

Bill Sherman
CH2M HILL / DEN
720-286-2792

-----Original Message-----
From: Scott Maxwell [mailto:smaxwell(--nospam--at)umich.edu]
Sent: Thursday, February 14, 2008 5:23 PM
To: seaint(--nospam--at)seaint.org
Subject: RE: IBC 2007 Wind calcs.

There is a BIG difference between being "not as easy as the UBC" and
being complex enough that it is tough to use.  I think that both Chris'
and my point is that we don't disagree that it is more complex than the
UBC, but it is also not hard to use (in our opinion).

Personally, I don't know how much of the grumbling is due to 1) people
not liking change; 2) people just not being used to it and have to
adjust to it; or 3) people just not understanding it because it is too
"complex" for them.
I suspect that a lot of it is #1 and #2 and that once people get past
those two issues (which time will solve), that #3 is really a non-issue.

Regards,

Scott
Adrian, MI

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