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

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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
> 
>