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Re: Code Created Malpractice Opportunity-Rigid v. Flexible Diaphragms

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Ben Yousefi Stated:

" By all standards of engineering science and the previous lab 
tests, these connections should have performed as assumed in design. The
weld 
was supposed to emulate the base metal performance and the steel was
assumed 
to be a homogeneous material, with identical and predictable properties in 
all direction. "

The above statement is wrong.  Previous lab tests had shown a large
variability in performance.  In addition the number of tests performed
prior to adopting the pre-Northridge connection were rather limited.  In
fact research performed shortly before Northridge questioned the
performance of the standard connection.

In addition the impact of material toughness, and the need to follow
welding procedures were well established before Northridge.  The problem
was that we did not follow the scientific process thoroughly enough.  The
information was out there but we were blind to it.  

Where are our blinders with regards to wood buildings?

The argument that we have not seen this problem in a previous earthquake is
questionable since it assumes that the nature of the construction is the
same as what survived the previous earthquakes, and that the previous
earthquakes were as large as we care to design to.  For example is a house
with few interior walls, many exterior windows, and a heavy tile roof the
same as an older house with smaller rooms, lots of walls, and a light roof.
 The answer is no, yet there is a common tendency to implement regulations
for building based on their occupancy as opposed to their physical
characteristics.

Considering the impact of diaphragm rigidity does not necessarily require a
sophisticated analysis if a little judgement is used.

Mark Gilligan