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

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Lynn,

We have had this very same discussion in the past.  My question would be
"what percentage of exterior wall is load bearing".  You do not indicate
whether this situation occurs at two locations per side or the entire
building perimeter.

The definitions of the two systems hinges on the amount of bearing walls in
the system.  A bearing wall system is where walls provide support for "all
or most" of the gravity loads, whereas a frame system is "an essentially
complete" frame system providing support for gravity loads, with lateral
loads resisted by shear walls or braced frames.

The intent is fairly clear to me in that a limited amount of shearwalls in
an otherwise complete frame system would qualify for the higher R factor.
If the entire perimeter is shearwall, like a warehouse facility, I would
question whether the column "inside the wall" on such a large percentage of
the structure could be classified as an independent space frame system and
would use the lower R factor.  If the columns where not integral with the
exterior and the shearwalls where a cladding like application I would go
back to the R of 5.5.

Clear as mud, right?

Paul Feather PE, SE
pfeather(--nospam--at)SE-Solutions.net
www.SE-Solutions.net
----- Original Message -----
From: "Lynn" <lhoward(--nospam--at)silcom.com>
To: <seaint(--nospam--at)seaint.org>
Sent: Thursday, January 30, 2003 6:34 PM
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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