From: Allen Adams <aadams(--nospam--at)ramint.com>
Date: Tue, 11 May 1999 08:54:17 -0700
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.
>Subject: 1997 Building drift limits
>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