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RE: 10/lw factor

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Stephen (spelled the same as my middle name:o)

I think you are on safe ground if you limit 10/lw to 1.0 maximum for wood
structures with plywood diaphragms. This is almost a non-issue based on all
of the published comments regarding the intention of the policy makers -
especially those of Dick Phillips who came up with the "Arbitrary" 10/lw

However, Dr. Goshen (spelling?) is highly respected in the profession and
his latest comments have all but guaranteed that there will be no limit for
masonry and concrete buildings where the diaphragm is known to act rigid. My
problem with Ron Hamburgers summary of Dr. Goshen's comments was that the
professional community expects to use the unrestricted limits to prevent
abuse within the community. This is the same as limiting an engineers
professional judgment when we, as a professional community, have been
extolling the need for competent engineers to rely heavily upon their
understanding and rationalization for mechanics and the subsequent
performance of structures.

As an example, the code restricts the aspect ratio of a shearwall to 2:1.
Does this mean that building official is obligated not to accept any designs
where the wall ratio exceeds this. Or, does it simply require the engineer
to prove by additional analysis that a narrower wall can be designed (as
would a proprietary shear wall) with appropriate stiffness despite the lack
of compliance to code?

Most of the engineers I spoke to about this will still design walls that are
greater than 2:1, however, they will study the deflection AND look closer at
the wall stiffness relationship to adjacent walls.

Where are we going with this code? It's one thing to educate engineers to be
aware of the issues regarding performance, stiffness, deflection etc.. It's
quite another to establish new restrictions that will prevent an engineer
from using his experience and knowledge!

Finally, to complicate matters; the issues of liability are completely
unrelated to interpretation of the code in this case. Inasmuch as there is
no expectation of tort reform and as long as engineers still debate
ambiguities written in the code (leaving issues to be interpretive) there
will always be a market for lawyers who know they can profit from the
insurance industries unprotected pot of gold as it is more expensive to
litigate than settle out of court. The state of law provides no protections
against frivolous lawsuits and our policy makers (SEAOC included) have done
nothing, in my opinion, to take the issues of liability serious enough to
work to protect their professional brethren.

Dennis S. Wish, PE

-----Original Message-----
From: Stephen Fisher's 400MHz [mailto:slf(--nospam--at)]
Sent: Friday, May 05, 2000 10:28 AM
To: seaint(--nospam--at)
Subject: 10/lw factor

The 97 UBC does not limit the 10/lw factor to a maximum value of 1.0 but the
1999 SEAOC blue book on page 8 does limit it to a maximum value of 1.0.  I
have read on this list that the current version of the IBC will limit 10/lw
for wood shear walls to a maximum of 1.0 but will not say anything regarding
concrete or masonry shearwalls.

It seems to me that the Blue Book should be enough to base our structural
designs on and therefore limit the 10/lw to 1.0 even though the 97 UBC does
not make the same statement.

	Am I going out on a legal limb?   What do you think?

	Stephen Fisher,SE