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Fwd: Building drift and separation

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Please note that the 1994 UBC says (I'm paraphrasing)  to use 3Rw/8 
=  0.38Rw, to caclulate the drift of each adjacent structure, but 
that the 1997 UBC will increase this requirement to  0.7R.  
Thus, the drift caclulation and building separation requirements will 
double in the 1997 UBC.

The use of R vs Rw will have no effect, since the lateral forces
used to caclulate the deflections were originally divided by R or
Rw. 

Also, there are some proponents who believe that the actual
expected drifts can be even higher, especially for short period
structures (less than about 0.5 sec), and that the 0.7R is really
only suitable for structures with longer periods.  Countering 
these arguements is the fact thatthe UBC requires the building 
separation to be calculated as the sum of the displacements of both 
adjacent structures, which is an absolute worst case assumption.  
Probabalistically, the square-root-sum-of-squares is a more likely 
maximum (which I do not recommend using, for reasons given above). 
Martin Johnson
EQE International, Inc.
mwj(--nospam--at)eqe.com



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From: "Martin Johnson" <mwj(--nospam--at)EQE.COM>
To: seaoc(--nospam--at)seaoc.org
Date: Fri, 18 Apr 1997 17:54:13 PST
Subject: Building drift and separation
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Richard Lewis, P.E.
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