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Re: drift calculation, 1997 UBC using ASD

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I pointed out this problem previously, but I can't find the original 
message to recycle it now.

You are correct.  The erratum is itself an error.  The original text 
was correct; deflections are to be checked using strength-level 
loads.  I suspect that someone at ICBO *thought* the section 
reference was wrong and prepared the erratum.  The codewriters that 
I've spoken to all agree that the original text was correct.  All 
other U.S. codes (including the 2000 IBC) are clear on this point.

> Thanks for alerting me to the printing error.  BUT does the errata make sense?
> If you compare Equations 12-6 (USD) and 12-10 (ASD), the USD equation will always
> provide a larger drift.  The drift limit of 2-2.5%H is a constant dependent only
> on building height. If the errata is correct then a building designed by ASD will
> always be permitted to have more drift than when designed by USD.  Regardless of
> the design method the drift used to compare to the maximum drift should be the
> same.  The only way to do this is to use the USD load factors.
> Incidentally, Appendix C (pg. 444) of the SEAOC Blue Book requires use of the USD
> (1612.2) equations when the design is otherwise ASD.

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Michael Valley                                   E-mail: mtv(--nospam--at)
Skilling Ward Magnusson Barkshire Inc.                  Tel:(206)292-1200
1301 Fifth Ave, #3200,  Seattle  WA 98101-2699          Fax:        -1201