# Omega Factor

• To: SEAINT(--nospam--at)seaint.org
• Subject: Omega Factor
• From: Tom.Hunt(--nospam--at)fluor.com
• Date: Tue, 21 Mar 2000 12:48:57 -0800
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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

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