First off, you only need to design the elements in the line of shear for the
revised R of the Cantilevered columns. You need not consider the other walls
in the same direction. A moot point since if you follow the letter of the
code you need to design the entire structure. The saving grace is the
explanation that appeared in the latest Blue book which allows you only to
consider the line of shear where the cantilevered columns occured.
The Plan checker probably does not realize that the majority of residential
one and two story structures will inevitably have a Rho less than 1.0 rather
than greater. I might argue this point but you can use the Shear in the line
of the Cantilevered columns but remember that the 10/Lw need not be less
than 1.0 (again, a error in the code which failed to consider wood walls and
was originally intended for use with masonry).
What really gets me is this mental masterbation required by the plan checker
when a change is made to the structure - something that occurs every day. If
the decorator decides to change another wall will you have to go through the
same gyrations? I suggest you bill the Decorator for the extra work and let
him/her think about the effects of the changes they make the next time it
This is a good argument for exemption or a simplified approach.
From: NDZ28(--nospam--at)aol.com [mailto:NDZ28(--nospam--at)aol.com]
Sent: Tuesday, February 01, 2000 8:15 PM
Subject: redundancy factor
I have a project ( 6000 sq. ft house) permitted a few months ago under the
94 UBC. Before contractor started construction decorator made some changes
to the window location in one wall. (Instead of two longer wall now I have
three shorter walls of about 6' each.) I checked with building official
and was told to design that wall line only to comply with the 97 code.
Since I had a pair of cantilevered columns in line with this shear wall I
used an R=2.2. Based on the soil report I ended up with a base shear of
about .56W/1.4=.45W. That's compared to the original factor of 0.183W.
Building official also wants me to also design for the Redundancy factor.
can Rho be determined under these circumstances. Any ideas or suggestions