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Re: Rigid Diaphragm Analysis

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In a message dated 5/8/99 8:21:06 PM Pacific Daylight Time, NDZ28(--nospam--at) 

<< What I want to know is how many of those involved in writing this code 
 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 
  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.    >>

I agree, though I do not know about this $20 billion that's been floating 
around. I do not believe that the actual structural damage was all that. 
Although a number of buildings sustained serious structural damage, most of 
the insurance payments were inflated due to cosmetic repair that may or may 
not have been caused by the Northridge earthquake. A crack over a door or 
window required the payment for patching and painting the entire room, and 
possibly sandblasting and restucco of the exterior. Some even went as far as 
adding new plywood, holdowns, etc. (you figure the cost), even though the 
structure was forty years old and was of "conventional framing." Which brings 
us back to the "Rigid/Flexible Wood Diaphragm" controversy. Will this design 
philosophy prevent a repeat of the Northridge Earthquake $20 billion cost? I 
think not. Because, cosmetic damage will still be a major cost factor as it 
was in the Northridge earthquake. And yes the construction defects, as 
witnessed then, will still be there to cause more damage, because the 
"rigid/flexible wood diaphragm analysis" will not eliminate them, if not make 
them worse:).


Oshin Tosounian, S.E.