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1997 Building drift limits

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In the 1994 UBC the drift limits (per Sect 1628.8.2) of 0.005 or 0.04/Rw,
etc., are based on the elastic displacements due to the specified forces,
which are working stress-level forces. By contrast, in the 1997 UBC the
drift limits (per Sect. 1630.10.2) of 0.025, etc., are based on the
so-called "Maximum Inelastic Response Displacement", which is 0.7R times
the elastic displacement (see Sect. 1630.9.2). Furthermore, the elastic
displacements are based on ultimate forces, not working stress-level
forces. Another way of looking this is to limit the drift to 0.025/(0.7R)
using the the elastic drifts. As you can see, the result is that the 1994
UBC and the 1997 UBC have roughly the same limits.
Allen Adams, S.E.
RAM International


>From: JSadler819(--nospam--at)aol.com
>Subject: 1997 Building drift limits
>To: seaint(--nospam--at)seaint.org
>
>I am concerned with the building drift limits of .025h per the 1997 UBC.  
>This is 5 times more drift than allowed by the 1994 UBC.  Designers and 
>engineers who engineer cladding systems such as windows, curtainwall, stone, 
>precast, signs etc.  are presented with serious problems with trying to deal 
>with this much drift.  I would like to hear from other listeners who are 
>scratching there heads on how to make attachments to buildings that drift 
>this much.

Jim Sadler