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Fw: UBC 97 Drift
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- Subject: Fw: UBC 97 Drift
- From: "T. Eric Gillham PE" <gk2(--nospam--at)kuentos.guam.net>
- Date: Sat, 27 Mar 1999 08:38:43 +1000
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----- 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
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 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, |
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