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RE: Omega Factor

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Tom,

Take a look at the 1997 NEHRP Commentary Section 5.2.3.3.  Take a look at
the last paragraph on page 72 and the top of page 73.  It appears that you
could consider it either way.

Also look at Section 5.2.6.2.3 of the 1997 NEHRP Provisions.

Regards,
Harold Sprague


> -----Original Message-----
> From:	Tom.Hunt(--nospam--at)fluor.com [SMTP:Tom.Hunt(--nospam--at)fluor.com]
> Sent:	Tuesday, March 21, 2000 2:49 PM
> To:	SEAINT(--nospam--at)seaint.org
> Subject:	Omega Factor
> 
> 
> 
> I have a structure (non-building but kinda building like) where
> transversely
> there are 8 steel moment frames space approximately 8 feet on center and
> in the
> other direction the structure has a shear wall from the top (elevation 70
> ft)
> down to 3 feet from grade.  The bottom three feet are open and forces are
> taken
> by weak axis bending of the columns.  Other than the obvious problems with
> soft/weak bottom story, the question is whether the bottom three feet of
> the
> columns would need to be designed based on omega times Eh??
> 
> One school of thought is that this is just one entire system (shear wall)
> on top
> of another entire system (cantilever columns) and you would just use the
> lower R
> value for longitudinal design.  The other thought is that this is a
> discontinuity and therefore requires the omega times Eh for the bottom
> portion
> of the columns.
> 
> Normally I have considered discontinuities as being when a portion of the
> structure is discontinuous and not when the entire system changes.
> 
> Which way would you see it??
> 
> Thomas Hunt, S.E.
> Duke/Fluor Daniel
>