In a message dated 5/8/99 2:31:44 PM Pacific Daylight Time, rjbossi(--nospam--at)sonic.net
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
ANDREW VIDIKAN, P.E.