Return to index: [Subject] [Thread] [Date] [Author]

RE: effective length factor for sway moment frames? K for frames wit h partially restrained connections?

[Subject Prev][Subject Next][Thread Prev][Thread Next]
I love Charles's answer. In my opinion, it shows true understanding of a not
only structural design, but life in general. We often think that buy
analyzing something to death we have come closer to the exact answer,
therefore, any amount of time and effort spent on that will be well worth
it. We overlook the fact that most everything in this world is relative as
Einstein proved, and our time is best spent striving for results that most
closely approximate the "exact" answers.

Enough philosophical thought on a Friday morning!

Ben Yousefi, SE
San Jose, CA

	-----Original Message-----
	From:	Charles Espenlaub [SMTP:Cespenlaub(--nospam--at)martinaia.com]
	Sent:	Friday, March 30, 2001 6:04 AM
	To:	seaint(--nospam--at)seaint.org
	Subject:	RE: effective length factor for sway moment frames?
K for frames wit h partially restrained connections?

	If it is a "theoretical" analysis, you may get "an" exact value.
But since
	theory is based on educated assumptions, the exact value you get may
not,
	and probably will not, be the "exact" value that occurs in nature.
Just
	because a computer can give you a four digit answer, does not mean,
	necessarily, that it is the right answer.


	Charles F. Espenlaub, III, P.E.
	Martin-Espenlaub Engineering
	Tel  215-665-8570
	Fax 215-561-5064



	-----Original Message-----
	From: Waterman Drinkwater [mailto:Drinkwater(--nospam--at)EQUATION.COM]
	Sent: Thursday, March 29, 2001 4:55 PM
	To: 'seaint(--nospam--at)seaint.org'
	Subject: RE: effective length factor for sway moment frames? K for
	frames wit h partially restrained connections?


	Try theoretical (FE) analysis. You may get the exact value.

	WD



	> ----------
	> From: 	Haan, Scott M.[SMTP:HaanSM(--nospam--at)ci.anchorage.ak.us]
	> Reply To: 	seaint(--nospam--at)seaint.org
	> Sent: 	Thursday, March 29, 2001 4:02 PM
	> To: 	IBC list (E-mail); Se-Practice List (E-mail); Seaint list
(E-mail)
	> Subject: 	effective length factor for sway moment frames?  K
for
	> frames wit h partially restrained connections?
	> 
	> Hello everyone,
	> 
	> The March "Modern Steel Construction" steel interchange has a
letter where
	> a
	> fellow asks if effective length factors can be unity for sway
moment
	> frames
	> when second order analysis is performed.  The fellow who responded
	> indicated
	> the effective length factor should still be calculated for
determining the
	> critical buckling column capacity.
	> 
	> 1997 UBC 2213.5.3 indicates K can be taken at unity when drift is
kept in
	> code limits and the columns are fixed at each joint.  I have an
old blue
	> book and the commentary indicates the code requires drift and
P-delta
	> consideration so K>1 is a further unecessary complication.  The
2000 IBC
	> adopts the "AISC Seismic Provisions for Structural Steel
Buildings" and it
	> does not appear to mention mention that the effective length
factor can be
	> taken as 1 for moment frame columns.
	> 
	> How are other places that are using the IBC handling this?
	> 
	> For fully restrained moment frames typically 1<K<2 unless the
beams are so
	> wimpy that there is no restraint.
	> 
	> What kind of effective length factor should be used for moment
frames with
	> partially restrained connections when the frames do not have drift
limits?
	> 
	> 
	> 
	> Thanks! 
	> 
	> Scott M Haan  P.E.
	> Plan Review Engineer
	> Building Safety Division http://www.muni.org/building, 
	> Development Services Department,
	> Municipality of Anchorage
	> phone: 907-343-8183   fax: 907-249-7399
	> mailto:haansm(--nospam--at)ci.anchorage.ak.us
	> 
	>