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Re: Rigid Diaphragm Analysis

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In a message dated 5/8/99 2:31:44 PM Pacific Daylight Time, rjbossi(--nospam--at) 
Bob Bossi wrote:

 I believe wood frame buildings (wood shear walls and diaphragms) should 
 qualify as "flexible"
 When we consider wood diaphragms combined with non wood elements (frames or
 concrete walls) then I think we need to be more careful.
 Bob Bossi >>

I agree with this statement. What makes this code section so ridiculous is 
the fact that when you're analyzing the roof diaphragm of a large (or small) 
all wood custom home (even if some steel columns or frames are present) with 
sloping roofs, dormers, hips, valleys, ridge beams, skylights, California 
roofs, how can this diaphragm even come close to acting as rigid element? 

What I want to know is how many of those involved in writing this code have 
extensive experience in designing wood structures as opposed to major 
concrete or steel structures, and how many had the opportunity to follow up 
on the performance of those structures after the '94 Eq?   

After inspecting over 500 wood framed buildings, mostly single and multi 
family dwellings for three years after the earthquake, it became evident to 
me that damage to most well engineered and detailed structures was nominal: 
it was my finding that lack of proper construction caused most of the damage. 
 Some of these buildings were built as far back as the 30's & 40's and I am 
sure that rigid diaphragm analysis was not even a figment of the imagination 
of the designer, nor of the builder, at that time.  Of the reported $20 
billion in structural damages from the earthquake, I wonder how much was 
inflated by the owner's through their engineer's structural reports to get 
more insurance company money.   

 The bottom line is it appears to me that some eager do gooder tried to bring 
the code into the 21st century and make an exact science out of wood 
construction.  But unfortunately what they failed to take into consideration 
is that the weak link in the chain is that the construction trades are 
operating in the dark ages.  Yes, we can perform our observations, but until 
the construction trades have to follow as stringent a compliance as we the 
engineers will be required to follow with this new code, I sincerely feel 
that no real improvement in the structural integrity of the buildings will be