----- Original Message -----
Sent: Friday, May 18, 2001 10:31 AM
Subject: RE: non compact pipe
Can't say I am 100% familiar with use of Q for pipes
but here is what I am seeing...
3" O.D. 14 gage thickness
= 3/.0747 =40.1
Compact Limit per Table B5.1 = 3300/Fy = 100 for 33
Based upon this it looks like D/t < limit ...
Section is Compact (Qs=1, Qa=1, Q=Qs*Qa=1) and needs no local buckling
Assuming the shape was not compact, it looks like you
are approaching it correctly:
Qs=1 for all pipes, no unstiffened elements exist in a round pipe or
rectangular tube either.
Qa appears to not be calculated for axially loaded circular sections since
they don't calc b sub e. Rectangular tubes should use eqn. A-B5-7 to
determine the effective width of the legs/sides. Other sections such as
I shapes would use A-B5-8 for their webs and Calc Qs as per
Keep in mind it states that Fa= minimum of A-B5-9 and section E2... longer
sections will probably tend to be controlled by E2.
Bending would be as stated, eqn F3-3... a Q adjustment is not "visible"
AISC, 9th Edition, ASD
For a non compact pipe, 3" dia. , 14 ga,
Appendix B5.2.a would have you adjust allowable
stress by the Q factor but.... equations for Q are for single angles, stems
of tees, with no mention of an applicable Q for pipe.
Am I correct in using B5.2.b equation A-B5-9
for Fa with no Q adjustment.
Am I correct in using F3.2 equation F3-3 for Fb
with no Q adjustment.