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# RE: NDS Equation 3.3-6 (CL)

• To: <seaint(--nospam--at)seaint.org>
• Subject: RE: NDS Equation 3.3-6 (CL)
• From: "Bill Allen" <T.W.Allen(--nospam--at)cox.net>
• Date: Fri, 2 Apr 2004 10:53:04 -0800

```Roger-

Well, Cd doesn't apply to short columns when they are end bearing on a plate
and Fcperp governs the design.

You wouldn't multiply the allowable stress by Cd=0.9 if the load was dead

If you don't buy Cd with regards to unbraced wood beams, what about steel
beams? If I had a cantilevered flagpole supporting a sign subjected to wind
loads and the WF flagpole had a reduced allowable stress due to unbraced
length (8th Ed. AISC F1.3), are you saying I can't multiply the allowable
stress by 1.33?

I'm sure there are many, many other examples where the capacity of a section
(using published code values) produce a reduced allowable stress which is
then multiplied by some form of a load duration factor. Yeah, yeah, I know
the "1.33" is disappearing from steel design, but it's not gone yet!

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

:-----Original Message-----
:From: Roger Turk [mailto:73527.1356(--nospam--at)compuserve.com]
:Sent: Friday, April 02, 2004 10:29 AM
:To: seaint(--nospam--at)seaint.org
:Subject: RE: NDS Equation 3.3-6 (CL)
:
:Bill,
:
:When the column design requirements were based on short, medium and long
:columns, Cd could only be applied to the short and medium columns.  When,
:in
:their infinite wisdom, AF&PA rewrote the column formula into a single
:formula, they said that they (somehow) included Cd in the short and medium
:portions of the formula, but did not include it in the long portion of the
:formula.  This is an accomplishment that truly deserves recognition.  I was
:not aware that they extended this accomplishment to lateral stability which
:never was stress controlled.
:
:I don't have my NDS at hand right now, but will be looking forward to a
:response from AWC.   (No response = Cd should not be applied.)
:
:A. Roger Turk, P.E.(Structural)
:Tucson, Arizona
:
:Bill Allen wrote:
:
:. > Roger-
:
:. > What about columns (when Fcperp doesn't govern)?
:
:. > In either case, NDS allows the use of Cd.
:
:. > T. William (Bill) Allen, S.E. (CA #2607)
:. > ALLEN DESIGNS (http://www.AllenDesigns.com)
:. > San Juan Capistrano, CA
:
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