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RE: Story Drift: 1994 UBC vs. 1997 UBC

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Thanks again, Ben.

FWIW, the 'allowable" deflection is more than twice that in the 94 code, in
fact it is 2.2 times (based on the work you provided below).

It WAS proper to include the 1.4 as you did since I for one take this out
almost immediately.

Sooo... in a wood framed structure with 8 ft. plate heights on a wall with a
LOT of glazing and containing inverted pendulums, flag poles or cantilevered
steel columns (whatever term is preferred), is it in fact allowable to
design to a drift of 0.011*8*12 = 1"? Are the design loads such that we no
longer are to be concerned about non-structural, collateral damage to
glazing, finishes, etc?

Regards,

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


> -----Original Message-----
> From: Byainc(--nospam--at)aol.com [mailto:Byainc(--nospam--at)aol.com]
> Sent: Thursday, August 12, 1999 9:44 AM
> To: seaint(--nospam--at)seaint.org
> Subject: Re: Story Drift: 1994 UBC vs. 1997 UBC
>
>
> bill
>
> 1- I stand corrected. I should not have included the term
> omega in the
> comparison, as Ron clarified in his posting.
>
> 2- in your OMF comparison if you drop the 2.8 for omega you
> will essentially
> get the same number as the 94 UBC
> => 0.025/4.5 = 0.0055
>
> 3- the 1.4 factor is already included in the calculations for
> base shear in
> the 97 UBC so you need not consider it in the drift
> calculations. The only
> reason I included it, was to make the compariosn more transparent.
>
> 4- In regard to the cantileverd column, with the revised
> comparion calc:
>
> delta97= (0.7)(1.4)(2.2)D94= 2.2 D94
>
> 0.025/2.2 = 0.011
>
> now this is almost double the allowable drift in the 94 UBC.
> However, if you
> note in the 94 UBC the limit was smaller of  0.04/Rw or
> 0.005. for Rw of 3
>
> 0.04/3= 0.013 ~ 0.011 (essentially the same)
>
> So, it appears that the lower arbitrary limit 0f 0.05 in the
> 94 UBC was left
> out of the 97 UBC and that is the reason for the discrepancy.
>
> Ben Yousefi, SE
> san Jose, CA