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Re: Residential Flexible/Rigid Diaphragm Analysis

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If the new flexible/rigid diaphragm or all other code changes triggered by the
Northridge Earthquake were meant to improve the performance of buildings and
limit the amount of damage to less than "safety-level" damage, then how does
one explain the fact that many structures on the same block with similar
design and construction, and sometimes older structures, suffered no or much
less damage than others. Two houses with similar design and construction, and
in many cases with identical floor plans, built on the same block or adjacent
lots, suffered dissimilar damage, one damaged beyond repair, the other had
minor damage.
I do not think that both were doomed because they were designed as flexible
diaphragms, and somehow God intervened and saved the one that housed a
believer. The truth is that there were factors other than the code required
design level that caused the damage in one house but not the other. How about
pour design, construction, inspection, or soil condition?

It's been customary to revise the code requirements after a disaster to
correct the "deficiencies" that were not "fully understood" "then." How about
now? Do we fully understand what caused the damage in one house and not the
other? Although, both were designed by the same designer based on the then
same code, and built by the same builder on two adjacent lots?

If "political" demand for higher code design level continues after each
damaging earthquake with no rational justification, then the future looks like

             V base= MW

Where M (multiples of W) => 1 and W=Total weight of building, including code
writers' weights, if more than 250 LBS, and the weight of any influencing
politician, if they represent an insurance company that is not willing to pay
up if a disaster occurs.

Oshin Tosounian, S.E.