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Re: seaint Digest for 31 Jul 1999

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Although the statics of torsion allow for two moments of opposite signs to 
reduce the capacity in the wall, the code still requires the results to be 
compared against the results of the flexible diaphragm analysis which is 
goverened by wind or seismic. If the shear due to torsion calculates at less 
than the shear by tributary distribution, the worst condition will govern.
The strange thing, in my opinion, is that the purpose is to balance the walls 
so as not to induce torsion. However, if you attempt to use the worst case 
shear, aren't you creating inequalities in the stiffness of the walls which 
work against rigidities due to torsion?

Dennis


In a message dated 8/6/99 1:35:12 PM Pacific Daylight Time, 
colin(--nospam--at)crosbygroup.com writes:

<< Mark & Dennis,
 
 I just came across the following message and have an additional question/ 
comment to
 add.
 
 I have also always been under the impression that the effect of torsional 
shears (even
 regardless of the many ways they appear to be calculated) could not reduce 
the overall
 shear force for a particular wall.  Mark,  this is something you stated at 
the end of
 you attached example.
 
 In reviewing Volume 1 page 78 of the Seismic Design Manual recently 
published by
 SEAOC, it is stated that torsional shears can be subtracted if they are due 
to the
 reduced eccentricity (e-e accidental).  Does anyone have any insight to this 
issue as
 it does appear to go against the intent of section 1603.3.3 of the 1994 UBC 
and what I
 also presume to be the implied intent of section 1605.2.1?
  >>