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RE: Light Gage Steel Framing: The Obvious Next Question

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My only concern with that approach is that you are putting your full faith
in a computer program not knowing whether it is doing it correctly or not.
Some of the off-the-shelf structural analysis programs do not calculate the
allowable stresses correctly for some mill shapes.  I personally have seen
incorrect calcs in mill angle allowables in one such program.  In case you
have not seen the AISI code it is considerably more complicated than the
AISC ASD/LRFD codes.  Each section must have "effective" properties
calculated which are based on the stress levels in the member (i.e.,
allowables will change as the loads change).  My personal view would be to
have some sort of feel for the numbers that the computer is calculating.
This "feel" will be difficult to judge if you are not familiar with what
should be going on behind the calcs.

As some of your later e-mails talk about, you are correct that the 96 AISI
is the latest code.  It does have a 1999 Supplement though (+- August).  The
AISI also has some additional texts which could provide some possible
details for this "dog house."  They are the "Prescriptive Methods for
Residential Cold-Formed Steel Framing - 2nd Edition", and the corresponding
commentary.  They are aimed at the residential market but I am sure some of
the details would work for commercial construction also.

Some other good sources of information re: cold-formed steel design are:  

1) Univ. of Missouri-Rolla offers a Cold-Formed Steel Short Course every 2
years in St. Louis Missouri.  It should be happening again this October.
Information regarding this seminar can be seen at http://www.umr.edu/~ccfss/
with contacts listed for additional information.

2) Cold-Formed Steel Design - 3rd Edition by Dr. Wei-Wen Yu... published by
Wiley Interscience  (info available on above web page also)

Also... don't forget to add your shear and overturning loads onto the
supporting structure.  If this addition is tall and/or on top of another
building along with the usual small foot-print of such a building the
overturning loads can become significant to the design of the lower
structure.

Attachment: If you are using steel deck on steel studs, typical attachment
would be with self-drilling screws.

Specs:
Wall Studs and Wall Stud Assemblies - 96 AISI Section D4
Connections: Welded (Section E2), Bolted (Section E3), Screw Connections
(Section E4), along with other applicable sections in Chapter E... (per 96
AISI)

Hope this information is helpful.  I do recommend as a minimum to attempt to
attend the above short course or equivalent to get a feel for what is
involved.  Remember the computer output is only as good as the input (and
maybe worse if the "black box" on the inside does not calculate what it is
supposed to correctly)... Good example is Windows... I am sure you have seen
an error message or two go accross your screen at sometime or another....
they have many good programmers (emphasis on many).  Most of the companies
that create the structural analysis software packages are very small
compared to companies like Microsoft.  If Microsoft can make a mistake so
can the small programming companies.  Long story short... If you know the
answer should be around 10 and get 13 then you are pretty comfortable.  If
you don't know a ballpark number, how do you know if 13 or 130 should be the
correct answer?

Anyway, enough soap box.

Hope above references are helpful!

Thanks,
Greg Effland, P.E.



-----Original Message-----
From: Bill Polhemus [mailto:bpolhem(--nospam--at)swbell.net]
Sent: Tuesday, January 16, 2001 8:23 PM
To: seaint(--nospam--at)seaint.org; aec-residential(--nospam--at)polhemus.cc
Subject: Light Gage Steel Framing: The Obvious Next Question


Well, now that I'm oriented as to section designations and what they mean,
the
next question (obviously) is "What is the latest design standard for light
gage"? "What is the methodology used currently"?

I am assuming that I would need the AISI design standard, but I don't have
one
right now (okay, I MIGHT be persuaded to drive down to Brown Bookstore in
Houston to pick one up, but since we've already had that discussion about
"two
hundred here and two hundred there, pretty soon we're talkin' real money!"
it is
obvious that I will resist that until absolutely necessary). My structural
design software will design-check these members for me. I can probably wing
it
with that and the design tables that the various manufacturers have been so
gracious to provide.

But may I use LRFD (since I've already got a steel model loaded up that
way)? Or
must I descend to the depths of "service loads" once again?

Any help you all could toss my way would be GREATLY appreciated!

Thanks.