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RE: Shear Wall Design

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Mark,
Actually, reviewing my comments, I pulled the figures for wind from an old
program I wrote. What I forgot to take into consideration is that I
increased the OT moment on the wall by 1.5 if wind governed - which is the
reciprocal of 0.666667. I realized this only after I sent the letter. Thanks
for bringing this up - it deserves correction.

Dennis

-----Original Message-----
From: Swingle, Mark [mailto:Mark.Swingle(--nospam--at)dgs.ca.gov]
Sent: Tuesday, November 16, 1999 2:59 PM
To: 'seaint(--nospam--at)seaint.org'
Cc: 'mswingle(--nospam--at)earthlink.net'
Subject: Re: Shear Wall Design


Dennis,

A minor correction.

Re: wind:
In the 94 UBC and the 97 UBC, the effective allowable dead load ratio to use
for resisting overturning is 2/3 for wind.  See 94 UBC 1619.1, 2nd
paragraph, and 97 UBC 1621.1, 2nd paragraph.  It is not 100%, but 67%.

Re: seismic:
In the 94 UBC, the effective allowable dead load ratio to use for resisting
overturning is 0.85 for earthquake, as you said.  See 94 UBC 1631.1, 3rd
paragraph.  In the 97 UBC, the second sentence of the corresponding
paragraph is removed from 97 UBC 1633.1, 3rd paragraph.  So the 85% no
longer applies in the 97 UBC.  Inquiring minds want to know.... what's an
engineer to do?  Well, now you get to use a load combination that had no
equivalent in the 94 UBC, namely 12-6 OR 12-10 OR 12-16-1 OR 12-18,
depending upon your situation (don't ask!).  And the winner is, 90%!!!!  (Of
course, this previously existed in some of the material chapters.)

This is the first item I have noticed that is more liberal than the previous
code.  Rejoice!

Mark Swingle, SE
Oakland, CA

--------------------------------

Dennis Wish wrote:

Therefore, you are permitted to consider 85% of the dead load on the wall
(for seismic) and 100% when wind governs to resist uplift on the wall (this
may have changed in the 97 UBC but I have not looked lately).