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RE: SEAOC seismology opinion regarding 10/Lw factor for calculating rho

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Thanks, Mark, for helping me to make my point. 

The distinction to be made with these proprietary shear panel substitutes is
that each model, although fabricated of many pieces, is pre-approved by a
code agency as a discrete structural, unitary element having listed
allowable and/or strength values. One employs those values in one's design
without further concern or inquiry into the internal construction of the
item. That's the whole idea: to have convenient, out-of-the-catalog
alternatives to conventionally engineered, jobsite-built shear walls. 

Further convenience and efficiency is found with  height-to-length ratios
typically narrower than now allowed in scratch-built wood shear walls. But
the reduction in Lw that is so attractive in them runs afoul of the
as-enacted Rho provisions (and still will, you say.) This dimensional snag
comes in spite of the fact that these proprietary assemblages are explicitly
tested and approved to be equal in performance to much wider conventional
shear panels. That equivalence is spoiled if their actual dimension, or
internal features of construction (like diagonal metal bracing) is allowed
to take precedence for Rho purposes over the package approval already achieved.

As has been revealed, the Seismology Committee that first foisted Rho into
code never contemplated these everyday realities in residential-type
engineering. The focus, fleetingly, was on industrial tilt-up walled
buildings. The Committee still appears not to have an adequately competent
grasp of their subject matter. A starting point for a third attempt might be
to revisit the basic aims of Rho: redundancy and reliability. See if shear
walls (of any sort) and their proprietary substitutes have any reliability
ills that are remedied by any form of Lw-based methodology. What other
approach might be better if any remaining need is in good faith proven? 

It is regrettable the extent to which code writing and code complying (and
later legal recriminations over code) have become a nitpicky parlor game
that entertains a few, but distracts and diverts most professionals from
getting on with their tasks efficiently and professionally. As Arnhem was in
retrospect a bridge too far, so is Rho for shear walls a code burden too
far.     

Charles O. Greenlaw SE
-------------------------------------
At 03:01 PM 11/22/99 -0800, you wrote:
>I don't think it leaves an ambiguity regarding a diagonal brace since that
is clearly covered under braces. Any diagonal brace counts as a brace. A
chevron brace provided 2 braces. The length of the braced bay is of no
significance, only the total number. Thus, a 4' long single brace
proprietary frame would count as one brace. If it were a shear wall it would
only count as 40% of a shear wall.
>
>Mark E. Deardorff
>
>> -----Original Message-----
>> From: Charles Greenlaw [mailto:cgreenlaw(--nospam--at)speedlink.com]
  ....
>> This proposal is appreciated and would appear to help in 
>> houses and other
>> small buildings, etc., but leaves ambiguous what happens in a 
>> basically
>> light-frame building where a proprietary steel diagonally 
>> braced frame is to
>> be used in lieu of a wood shear wall, or some other non- "light frame"
>> element like a Simpson Strong Wall or a steel moment column 
>> or moment frame
>> is to be used.