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Re: Dynamic drift calculations (1998 CBC/1997 UBC)

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"If you are comparing service level deflections to an
allowable based on strength level loading you are comparing apples and
oranges, and in this case allowing 40% greater deflection levels than
intended."

Exactly my point.  The drift limits are given for the strength level forces.  So regardless of the design method used to size the members, you must use the strength level load combinations for calculating drifts.  Or you could reduce the drift limits, but you must be consistent.

Jason Emoto 

>>>"Paul Feather" <pfeather(--nospam--at)san.rr.com> 12/15/00 01:12PM >>>
Yes, deflections are deflections, but the comparison criteria is dependent
on the loading.  If you are comparing service level deflections to an
allowable based on strength level loading you are comparing apples and
oranges, and in this case allowing 40% greater deflection levels than
intended.

Paul Feather
----- Original Message -----
From: "Jason Emoto" <jemoto(--nospam--at)reidmidd.com>
To: <seaint(--nospam--at)seaint.org>
Sent: Friday, December 15, 2000 10:37 AM
Subject: RE: Dynamic drift calculations (1998 CBC/1997 UBC)


They need an errata list for their errata list.  Deflections are not a
function of design methodology.  Your structure won't know or care whether
you use ASD or LRFD.  Think of a beam with a point load at midspan.
Regardless of whether you used ASD or LRFD to size the beam, the deflection
will be Pl^3/48EI.

Jason Emoto