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I am not all that familiar with UBC97, and besides Eddie G has already provided what seems to be a reasonable response to the actual code reqts.
 
My comment is general in nature:
 
If you think about the basis for seismic design in general, I think it is apparent that cracked sections MUST be used when computing both structural properties for seismic analysis, as well as expected deformation levels.
 
Remember that the expected accelerations during the actual design EQ are much much higher than those assumed for an elastic analsysis.  This being the case, even if your walls don't crack under ELASTIC forces, they almost certainly will during the actual earthquake.  The elastic analysis used by most designers doesn't really have much relation to the actual inelastic performance of the structure being designed during a real earthquake, primarily because one is elastic, the other inelastic.
 
In structures I have designed for seismic performance, I usually tend to be quite conservative with regard to expected deformations, perhaps because I do mainly R/C work.  I feel strongly that a displacement based approach to seismic design is much more rational than the current force based approach, so that is probably part of it as well.
 
T. Eric Gillham PE
GK2 Inc.
PO Box 3207  Agana, Guam  96932
Email - gk2(--nospam--at)kuentos.guam.net
Ph:  (671) 477-9224
Fax: (671) 477-3456
-----Original Message-----
From: Sleiman Serhal <mony(--nospam--at)destination.com.lb>
To: seaint(--nospam--at)seaint.org <seaint(--nospam--at)seaint.org>
Date: Friday, March 26, 1999 7:04 PM
Subject: UBC 97 Drift

When computing Ds for a shear wall according to the UBC 97, do u use in your mathematical model an I of 0.35Ig if the wall cracks under elastic forces - due to E only

It seems to me that this would be too penalizing especially that we multiply Ds by the R factor to get Dm which is the value actually used to determine if the allowable drift has been exceeded.

Some engineers tell me they use an I = 1Ig !

And is the 1.2D + f1L + E including P-D  the only combination to use for drift calculations ?
 

Thanks in advance,
Moni Serhal