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Rw Factor with additional Question comparing Rigid Diaphragm Analysis.

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If you are dealing with a box system - light gauge framing and are using
plywood shear walls, you may use an Rw of 8. If you are considering Gypsum
or Stucco as your shear elements (although I don't recommend this) you must
use an Rw of 6. If you use a braced frame (correct me if I am wrong) as part
of your box system, then use an Rw of 6.

In my opinion, using Rw as 6 when 8 is applicable is a very smart approach
that keeps helps compensate for potential field defects.

This poses an interesting question - Has anyone compared the wood design
example done by Bill Nelson which was part of the SEAoSC wood seminar last
February to a flexible diaphragm analysis using plywood shear walls and an
Rw of 6?

I reviewed Bills design example and would like to poses this observation -
although I have not looked at other examples to see if this a valid
In Bill's example (and Bill, feel free to jump in anywhere here - please),
he provided both a flexible analysis and then a rigid analysis. Rather than
use the results of one or the other, he chose to use the more conservative
results down each line of shear from both analysis.
Comparing results it seemed that Flexible diaphragm analysis was more
conservative for longer shear walls and rigid analysis  governed when walls
approached their maximum aspect ratio. Therefore, why bother to go through
such an extensive analysis (considering that you must still design for Wind,
Seismic - Flexible and Rigid) in order to compare results and use the worst
case situation for each.
1. The resulting shears are not representative of one condition that governs
at the time of action
2. The observation that narrower piers require more shear to be absorbed by
more rigid elements.

Therefore, why not simply stipulate an arbitrary constant to apply to all
shearwalls that fall within a specific aspect ratio range?

Dennis Wish PE

-----Original Message-----
From: T. Eric Gillham [mailto:gk2(--nospam--at)]
Sent: Monday, November 16, 1998 3:37 PM
To: seaoc list
Subject: Fw: Rw Factor

Not sure if this is a first post or not.  If it is, then more information
would be needed to answer, beyond the simplest one of "Check the
appropriate code table against the structure you are designing (e.g.
concrete bearing wall system vs. concrete shear wall system wherein walls
take minimal gravity loading)".

T. Eric Gillham PE

> From: LAMPSMITH(--nospam--at)
> To: seaint(--nospam--at)
> Subject: Rw Factor
> Date: Tuesday, November 17, 1998 1:36 AM
> Criteria for selecting Rw factor of 6 vs 8?