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RE: 97 UBC 1633.2.4 Deformation compatibility - is that a typo?

• To: <seaint(--nospam--at)seaint.org>
• Subject: RE: 97 UBC 1633.2.4 Deformation compatibility - is that a typo?
• From: "Bill Allen" <Bill(--nospam--at)AllenDesigns.com>
• Date: Mon, 15 Nov 1999 21:54:16 -0800

```I believe you are running into one (yet another?) of the weaknesses of the
UBC code which is Confusion. The Delta-sub-M term is, first of all, based on
factored loads which, by now, you have probably factored out by dividing
your shear by 1.4. That's Delta-sub-s.  Well, put it back in. Next, multiply
Delta-sub-s by R and you have Delta-sub-m. NOW, compare to 0.025H.

One issue that is really bothering me. You know, in the 1994 code,
deflection ALWAYS governed cantilevered columns? Well, not any more (R=2.2).
You know how we NEVER worried about deflection with plywood shear walls?
Well, not any more (again, because of R).

IMO, I STILL think it is prudent to look at the ASD loads and compare it to
0.005H.

Bill Allen, S.E.
ALLEN DESIGNS
Laguna Niguel, CA

||-----Original Message-----
||Sent: Monday, November 15, 1999 4:12 PM
||To: seaint(--nospam--at)seaint.org
||Subject: RE: 97 UBC 1633.2.4 Deformation compatibility - is
||that a typo?
||
||
||Mark - Right On. I thought 0.025H was wrong until I read the
||design example
||in the ICBO Seismic Design Guide. It is 0.025H (0.025 x H(ft)
||x 12(in/ft))
||for period T less than 0.7 seconds and 0.020H for T<=0.7. This is a
||tremendous deflection - over 3.6" for a 12' story.
||What I don't understand is why. It was my understanding that
||the past codes
||set story drift at 0.005H (L/240) which is about 0.72" for a 12' story
||height.
||
||If the code is correct then how in heck will a diaphragm of
||plywood ever
||calculate a flexible if the diaphragm deflection based on 2.5
||times the
||blocked diaphragm calculates in the code is still less than 0.005H?
||
||Dennis
||
||-----Original Message-----
||From: Swingle, Mark [mailto:Mark.Swingle(--nospam--at)dgs.ca.gov]
||Sent: Monday, November 15, 1999 4:08 PM
||To: 'seaint(--nospam--at)seaint.org'
||Subject: 97 UBC 1633.2.4 Deformation compatibilty - is that a typo?
||
||
||The first paragraph of the above section (97 UBC 1633.2.4 -
||Deformation
||compatibilty) appears to have a typo.
||
||Reference is made to a drift (deltaM) of 0.0025 times the
||story height.
||
||Shouldn't that be 0.025?
||
||Mark Swingle, SE
||Oakland, CA

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