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
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
Subject: seismology committee
Since we seem to have started another round of seismology bashing, I
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
to occur with minor structure changes. Gary Searer's letter used these
fuctions to argue his point by showing these exaggerations. Currently a
within SEAONC is meeting and having discussions about a possible revamp.
part of this, Ron Hamburger wrote an interesting paper in which he used
probabilistic design methods to show that the concept of redundancy has
in improving the margin against collapse - in other words, that we should
necessarily throw the entire concept of redundancy out. It is probably
take several months for this committee to work something out.
I have personally pushed for a code change proposal for the IBC 2002
(and also in ASCE-7, which will be the basis for the NFPA code) to allow
free use of flexible diaphragm assumptions in light-frame construction
without having to perform an analysis to justify the analysis methodology
The down side is that it is going to be within the "simplified method"
a 25 percent penalty in lateral force. Personally, I do not like the
method of analysis. In it's pursuit of defining what the maximum force in
one element might be, it overlooks the big picture, in that the next
of base shear is significantly increased relative to what has historically
seemed to be adequate. The only justification for the approach is that it
way to satisfy a reviewer without more elaborate analysis. Putting up with
percent penalty may actually result in lower base shears than using an
procedure, with significantly less work.
I have for a year been pushing for the committee to take a fresh look at
irregularity tables, which also contain curious step functions. (why is it
special design rules for an in-plane offset of a plywood shear wall
kick in when the length of offset is equal to the length of wall? Does a
or two really make that much difference? Certainly the wall holdown
notice the difference.) Finally that work is getting started.
We are looking hard at the FEMA 350 documents and developing
help engineers to interpret their use. Basically, we are putting the
who developed the SEAOSC document that has been published on their web
which some engineers have argued as being too conservative, into a room
some SEAONC engineers, and letting them slug it out. They are actually
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
is focussed on large or unusual buildings (what I called a "Blue Book
Probably something will be done about this in the next few years, although
can't at this time see what can be done about the complexity of the
design sections that have been developed and put into the code by AISC,
ACI. etc. The SEAOC eventual product probably cannot be presented in the
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
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
that were "about right."
We have also been doing some more esoteric work such as working with AISC
develop guidelines for designing BRBF systems, reviewing the findings of
PRESS test program, and working to develop more rational methods for
seismic design (which is progressing very slowly).
While there is no end of things to do, there are definite limits on the
energy of the engineers to pursue them. Nothing gets done quickly, it
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
power in defining building codes. The BSSC committees that develop the
provisions probably have the most influence in that regard, and those
are deliberatly balanced between practicing engineers, academicians,
and building officials (so much for the "practicing engineers only"
WIthin SEAOC there has been a movement to move the seismology committee
from direct code development towards basic science and to find ways to work
closely with national organizations such as BSSC and NCSEA. Within the
seismology committee, our code change proposals for the IBC supplement had
argued to the NCSEA to gain their support for submittal to the IBC. So
was an entire layer of review between us and the code process. That aside,
still do a very thorough review and take positions on of code change
developed by other parties as well as the NEHRP draft documents.
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