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RE: Proper seismic R factor to be used in concrete design

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I side with the Building Frame position. The racking of wall potentially
creates some diagonal cracks in the wall and some yielding at the boundary
zones. But, in my opinion,  would not seriously harm the column's vertical
load bearing capacity. The catch would be that the column should be detailed
as a columns that is part the lateral force resisting system (i.e. properly
confined, etc.). 

Ben Yousefi, SE
San Jose, CA

 -----Original Message-----
From: 	Lynn [mailto:lhoward(--nospam--at)silcom.com] 
Sent:	Thursday, January 30, 2003 6:34 PM
To:	seaint(--nospam--at)seaint.org
Subject:	Proper seismic R factor to be used in concrete design

Dear members of the list:

I have a question that seems to have different
engineers giving different opinions of the appropriate
R factor that should be used for a concrete building we
are involved with.

The building is a shear wall system.  The floors and
roof are concrete constructed of slabs and supporting
beams and girders.  The girders frame into the center
of each exterior concrete shear wall.  Inside the
exterior wall, there is a tied column designed to carry
the gravity loads of the girders.  The columns are dead
center along the length of the wall.

The question is:  Is this a "building frame system"
using concrete shear walls (R=5.5), or a "bearing wall
system" with concrete shear walls (R=4.5)?

The argument for the R of 5.5 is that the shear wall
itself is not load bearing, since there is a column
embedded dead center in the wall designed to carry 100%
of the gravity loads as a column.

The argument for the R of 4.5 seems to suggest that if
the shear walls yields under seismic forces, the
capacity of the column may be jeopardized, so the
girders do in fact rely on the structural integrity of
the shear walls to carry the gravity loads of the
floors.

Any comments or recommendations would be appreciated.

Thanks

Lynn

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