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Re: Lynn's comments and Vision 2000 objectives

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In a message dated 7/31/99 5:02:39 PM Pacific Daylight Time, 
lhoward(--nospam--at)silcom.com writes:

<< I do not agree with the philosophy that the Code should require that
 structures should be able to go through a design based earthquake and
 suffer little damage.  The Engineer and Owner have the prerogative of
 designing to a higher standard than the Code requires, and we often do
 that here in our office.  However, in my opinion, the minimum
 requirements of the Code should only provide life-safety protection for
 the occupants.   >>

Lynn,
Again, I agree with you entirely. While reviewing the Blue Book Draft, 
reference was made to compliance to the Vision 2000 objectives. I turned to 
Appendix B of the 1996 Blue book and started to read about Vision 2000. 
I came to the conclusion that we would be opening ourselves to serious 
liablity if we tried to design wood structures based on these code provisions 
with the prospects of predicting the level of performance in wood structures.
The Blue Book draft did one thing very well - it defined no less than 8 or 10 
elements important in the execuation of the stiffness design provisions 
(rigid diaprhagmand wall stiffness distribution) that negates any possible 
conclusion that can be drawn from the method for wood structures. 
In Appendix A of the 1996 Blue Book, the evaluation of damage from the 
Northridge earthquake is more than adequate to suggest changes (which became 
part of the Los Angeles emergency measures) including increase sill 
thickness, larger plate washers and consideration of nail bending and 
slippage and holddown deflection due to wood shrinkage. I highly recommend 
rereading this section of the '96 Blue Book which leads on to wonder just why 
the Seismology committee has taken such drastic measures to enforce a 
methodology that is unproven and lacks sufficient emperical data to justify.
The only reasonable conclusion that I have been able to make is that they 
need to tie up all sections of the code to be compliant with the provisions 
of Vision 2000. I personally believe that they believe the methods used for 
concrete diaphragm is applicable to all building materials and that what is 
not sufficient can be "tweaked out" in due course.
This puts them one step closer to meeting their goal of adoption of the 
Vision 2000 goal. The problem is that it is too flawed when it comes to wood 
structures because of all of the unknown variables. Expectations can not be 
met by what evidence we currently have from past earthquake damage.
Structures with embedded Cantilevered Columns, for example, are designed to 
penalize the entire structure with a lower R (2.2) used to inflate the base 
shear in the direction of applied load only because of the perceived 
deficienceis documented from buildings with "tuck-under" parking. No 
consideration is given for other types of structures which rely upon embedded 
columns but whose diaphragms may contain discontinuities due to separage or 
elevation changes and the Sesmology group is not willing to comprimise from 
the letter of the code. Therefore, they are willing to penalize all 
structures without regard to physical constraints of the diaphragm. For 
example, there is no exception to the rule when the columns are used at the 
edge of patio covers where the patio roof exists at a different elevation 
thatn the main structure. You can not convince me that the the adjacent 
diaprhagm will be affected by the displacement due to torsion of the patio 
roof when securely attached to a shearwall supporting both diaprhagms.
The other discrepency is in the Rho factor as acknowledged by both Charles 
Greenlaw and Ron Hamburger. No comprimise and strict compliance with the 
letter of the code.

To base a code on a prediction of performance when there is no supporting 
evidence to suggest design deficience is not valid. This is the reason that I 
believe the Seismology committeeis trying very hard to tie up the expected 
performance of all materials under the same code provisions and failing to 
admit that most wood buildings should be placed in a separate class. 
Seismology also fails to acknowledge or accept that residential buildings 
represent over 80% of all building constructed in this country. therefore to 
commite the practicing professional community to predict the performance of 
wood structures is to expose us to possible litigation once damage occures.
This, in my opinion, is irresponsible at best.

Dennis S. Wish PE