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RE: Accidental Torsion

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You know, this is the way I had thought about it for years until Neil
Moore's post. I had always thought that the design eccentricity was EITHER
the calculated eccentricity or 5% of the building dimension, whichever was
larger. However, as Neil pointed out, the Code states "..PLUS and accidental
torsion." So, you have to consider the actual eccentricity, plus (or minus)
5% of the building dimension.

It's funny (not really), but with the additional requirements of calculating
stiffnesses of wood shear walls, it is becoming apparent that it is no
longer practical to do seismic design of wood structures (when performing a
rigid diaphragm analysis anyway) by hand. With all the variables and
"engineering judgement" involved, I would think it would be difficult to
verify the basis of the software programs that are designed to perform this
function. For example, the shear wall deflection methodologies are different
from the example presented in the SEAOC seminar in February, 1998 and the
Seismic Design Manual, Volume 2.

Soooo....we've got to envelope:

1. Results based on Flexible Diaphragm Analysis
2. Results based on Rigid Diaphragm Analysis based on an eccentricity of
actual plus 5% of the building dimension
3. Results based on Rigid Diaphragm Analysis based on an eccentricity of
actual minus 5% of the building dimension
(or just number 2 and don't subtract the torsional effects)
4. Oh yeah, wind loads.

Based on the published equations for shear wall deflection, wood shear wall
stiffness is not linear. How many times should this be iterated? Also, how
many iterations do you have to perform to calculate A-sub-x?

Regards,

Bill Allen, S.E. (CA #2607)
ALLEN DESIGNS
Laguna Niguel, CA
http://www.AllenDesigns.com

||-----Original Message-----
||From: sscholl2(--nospam--at)juno.com [mailto:sscholl2(--nospam--at)juno.com]
||Sent: Monday, July 03, 2000 8:29 PM
||To: seaint(--nospam--at)seaint.org
||Subject: Re: Accidental Torsion
||
||
||I guess you would try to figure what torsional forces would
||likely affect
||the structure and design to resist them. For example in
||certain types of
||structures a vehicle can run into it from any angle.  Who is
||asking this?
||
||Stan Scholl, P. E.
||________________________________________________________________
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