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RE: AISC Appd. 'B' - Qs

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Rich,

Your on the right track...

1) If when calculating Qa you get an effective width (be) greater than or
equal to the actual width (b) then you are correct using Qa = 1.0.

2) For a tube column there are no unstiffened compression elements therfore
Qs = 1.0.

Q= Qs * Qa

Make sure you use Q in the Axial allowable as per Eqn. A-B5-11 and to limit
allowable bending values to <= 0.6*Fy*Qs (insignificant in this particular
case since Qs=1) and modify equations H1-2 and A-F7-13 as per Appendix
B5.2.d

HTH,
Greg Effland, P.E.
KC MO

-----Original Message-----
From: richard lewis [mailto:rlewistx(--nospam--at)juno.com]
Sent: Tuesday, July 31, 2001 4:51 PM
To: seaint(--nospam--at)seaint.org
Subject: AISC Appd. 'B' - Qs


I have a question regarding using AISC Appendix 'B'.  I have a HSS
10x10x1/4 column with axial load and bending.  The b/t ratio of 39.9
exceeds the noncompact requirement which makes me check Appd. 'B'.  A
tube is a stiffened compression element which uses Section B5.2.b to
calculate the effective width.  

As I understand it the 'f' value is the stress in the flange of the tube
from bending and axial load.  This is used to calculate the effective
width of the tube.  In my case the 'f' value is 19.7 ksi.  This makes the
effective width 'be' = 9.51 inches.  The real width of the tube flange is
9.30 inches (39.9*the thickness of 0.233 inches of the flange) so I can
use the real section properties of the tube because these are less than
the 'be' properties.  'Qa' will then equal 1.0.   Is this correct?

How do I calculate 'Qs' for the tube column.  Appd. 'B' Section B5.2.a is
for unstiffened elements.  What is the equation for a stiffened element
of a tube?

Rich
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