I am curious to know why ICBO has decided to bring this issue to the
forefront recently. Has there been any documentation of serious damage to
wood diaphragms or shear walls that were proven to be the result of assuming
the diaphragm as flexible? If the diaphragm is assumed to be flexible, and
in reality, because of its geometry it acts more like a rigid diaphragm,
some of the walls may get more lateral load induced in them than intended.
In my humble opinion, in a light framed wood structure the additional load
can easily get redistributed (similar to the assumption we make for concrete
beams and slabs) and eventually the other overdesigned walls will pick up
the slack. I can't imagine how this assumption would lead to serious
negative implications as it would with concrete or composite metal deck
diaphragms. I would be very interested in receiving any factual
documentation that can shed some light on this issue.
From: Seaintonln(--nospam--at)aol.com [SMTP:Seaintonln(--nospam--at)aol.com]
Sent: Tuesday, May 04, 1999 1:16 PM
Subject: Re: Changing the code (followup to Rigid Diaphragm)
/ '| From the Desk ()_________)
\ '/ \
(__) Dennis S. Wish PE
I receive my list messages in digest format. I read all of the
arguments related to the issue of code development and trying to
for the better.
Chuck Greenlaw is most closely akin to my belief's but in a much
eloquent way (I wish I could write like that). Barry Welliver
comments and reflected many of the same feelings I have on the
Rick Ranous has been a long time associate and I respect his
However, he may be missing an important and urgent liability issue:
The provisions for rigid diaphragm analysis have been in the code as
1988 (as pointed out by another of our list members) and has been
the same as
the '97 code since 1994.
Tom Campbell pointed out (and I tend to agree) that the attention to
diaphragm analysis started when ICBO began doing seminars in 1998
preparation of the '97 code changes. Little did we realize what most
were missing from the '94 code.
How liable are we? If a building owner decides to sue an engineer
(whether a valid suit or not), how will the engineer fight the
issue when an expert witness points out his failure to comply with
provisions of the '94 code?
What are we doing as a professional community to protect ourselves
potential liability when we choose by professional judgment and with
aceptance of the local building official to deviate to a lesser
Tom reminded me that the code provides the minimum standard and that
engineers may do more than this. However, what happens when the
standards are considered excessive? What is the engineers
liability when he or she choses to do less than the code recommends?
I don't think that we can wait for the next few code cycles to
In support of Rick's comments, I contacted Tom Campbell from ICBO
morning. He was more than willing to work with us to provide
information as it develops. I suggested that he contact Bruce Bates
the chair for the Computer Applications Committee of SEAOSC to start
rolling and that their efforts can work into a site on our website
discussions on this List. Tom's offer was the first real sign of
I've seen occur in a while and I applaud him.
Rick, I agree with Chuck Greenlaw that we are caught in a muddle of
and that most code committees welcome comments as long as they don't
or adversly affect approval scheduling. We can make change as you
but only with cooperation from those in a possition to shepard our
and suggestions and assure us that they are given proper
Unfortunately, we are a society of the apathetic - silent majority
want to observe and not participate. I wish they would but this may
reason that change is so slow in occuring.
Any good suggestions as to the liability issue?
Dennis S. Wish PE
Structural Engineering Consultant