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Re: seismology committee

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Martin:

It's a shame that somebody decided to resurrect the recurring ListServer
pastime of blaming the SEAOC Seismology Committee for things beyond its
control.  I was glad to see that the committee volunteers are still hard at
work addressing current and future issues that concern all the California
Structural Engineers.  Thanks for presenting some facts on the current
committee activities.

And thanks to the entire SEAOC State Seismology Committee, past and
present, for your countless volunteer hours representing California
Structural Engineers through the lengthy bureaucratic building code
approval process.  Your efforts are appreciated.

Rick Drake, SE
Fluor Daniel, Aliso Viejo, CA

******************************





"Martin W. Johnson" <MWJ(--nospam--at)eqe.com> on 02/07/2001 10:40:54 AM

Please respond to seaint(--nospam--at)seaint.org

To:   seaint(--nospam--at)seaint.org
cc:

Subject:  seismology committee




Since we seem to have started another round of seismology bashing, I
thought I'd
mention a few things that the committee has been doing;

We have had discussions about the rho factor.  Clearly it is arcane and not
easily justifiable.  It has curious step functions which cause wide
variations
to occur with minor structure changes.  Gary Searer's letter used these
step
fuctions to argue his point by showing these exaggerations.  Currently a
group
within SEAONC is meeting and having discussions about a possible revamp.
As a
part of this, Ron Hamburger wrote an interesting paper in which he used
probabilistic design methods to show that the concept of redundancy has
validity
in improving the margin against collapse - in other words, that we should
not
necessarily throw the entire concept of redundancy out. It is probably
going to
take several months for this committee to work something out.

I have personally pushed for a  code change proposal for the IBC 2002
supplement
(and also in ASCE-7, which will be the basis for the NFPA code) to allow
more
free use of flexible diaphragm assumptions in light-frame construction
(i.e.,
without having to perform an analysis to justify the analysis methodology
used).
The down side is that it is going to be within the "simplified method"
which has
a 25 percent penalty in lateral force.  Personally, I do not like the
"envelope"
method of analysis.  In it's pursuit of defining what the maximum force in
any
one element might be, it overlooks the big picture, in that the next
summation
of base shear is significantly increased relative to what has historically
seemed to be adequate.  The only justification for the approach is that it
is a
way to satisfy a reviewer without more elaborate analysis.  Putting up with
a 25
percent penalty may actually result in lower base shears than using an
envelope
procedure, with significantly less work.

I have for a year been pushing for the committee to take a fresh look at
the
irregularity tables, which also contain curious step functions.  (why is it
that
special design rules for an in-plane offset of a plywood shear wall
suddenly
kick in when the length of offset is equal to the length of wall?  Does a
foot
or two really make that much difference?  Certainly the wall holdown
doesn't
notice the difference.) Finally that work is getting started.

We are looking hard at the FEMA 350 documents and developing
recommendations to
help engineers to interpret their use.  Basically, we are putting the
engineers
who developed the SEAOSC document that has been published on their web
site, and
which some engineers have argued as being too conservative, into a room
with
some SEAONC engineers, and letting them slug it out.  They are actually
coming
to an agreement, thanks to the hard work of Bob Lyons.

We have held discussions about the possibility of developing some sort of
small-building design document, that would strip out a lot of the clutter
that
is focussed on large or unusual buildings (what I called a "Blue Book
Lite").
Probably something will be done about this in the next few years, although
I
can't at this time see what can be done about the complexity of the
materials
design sections that have been developed and put into the code by AISC,
AF&PA,
ACI. etc.  The SEAOC eventual product  probably cannot be presented in the
form
of an "alternative code," since building officials only want to adopt and
enforce a single code, but rather as a subset document that would just
extract
out the contents of the current code.  Another model is the old "Simplified
Design" document that was published by PCA a number of years ago, which
presented simple rules-of-thumb equations that could be used to generate
designs
that were "about right."

We have also been doing some more esoteric work such as working with AISC
do
develop guidelines for designing BRBF systems, reviewing the findings of
the
PRESS test program, and working to develop more rational methods for
foundation
seismic design (which is progressing very slowly).

While there is no end of things to do, there are definite limits on the
time and
energy of the engineers to pursue them.  Nothing gets done quickly, it
takes
months to review things and develop a consensus.

What we have NOT been doing is being a hidden behind-the-scenes dictator of
building codes.  Actually, the seismology committee does not have all that
much
power in defining building codes.  The BSSC committees that develop the
NEHRP
provisions probably have the most influence in that regard, and those
committees
are deliberatly balanced between practicing engineers, academicians,
producers
and building officials (so much for the "practicing engineers only"
arguement).
WIthin SEAOC there has been a movement to move the seismology committee
away
from direct code development towards basic science and to find ways to work
more
closely with national organizations such as BSSC and NCSEA.  Within the
seismology committee, our code change proposals for the IBC supplement had
to be
argued to the NCSEA to gain their support for submittal to the IBC.  So
there
was an entire layer of review between us and the code process.  That aside,
we
still do a very thorough review and take positions on of code change
proposals
developed by other parties as well as the NEHRP draft documents.

regards,
Martin











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