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[SEAOC] Re: [SEAOC] Rw factors

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At 01:38 PM 11/8/96 -0500, MGFran(--nospam--at)aol.com wrote:
>I would like to know what other engineers have been using for Rw with the
>following conditions: Flexible diaphragms using plywood shear walls mixed
>with steel frames on both residences and commercial structures.
>
>We have conservatively used the lowest value for Rw for all lateral force
>resisting elements in the structure in the past, but it seems that one could
>justify using an 8 for the plywood shear walls and a 6 for "Ordinary" steel
>moment frames, for example, since the diaphragms are flexible and the shears
>are distributed based upon tributary area.

Better safe (conservative) than sorry, I've always used the equivalent of
Rw=6 for any wood framed structure. I do this because I feel that most
architects would prefer to skimp on walls and provide as many openings as
possible. With and Rw factor of 6, you can design the narrower shear
elements (wood piers) for a more conservative stiffness based upon shear
wall deflection criteria from the '91 UBC Standards.
Inasmuch as there is a question regarding adequate design methodology for
story drift in a plywood shear wall, it seems most prudent to use the
current standard and apply a higher force - determined by using Rw=6.0

That's my two cents, for what it's worth.

Dennis S. Wish PE

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