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RE: Drift per 1997 UBC

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The 97 UBC represents a considerable departure in method and theory from the
94 UBC.  Many values have changed, but I wouldn't describe anyone as having
"gotten a break".  It is just different.  If a building benefits from these
changes, I don't see why that is grounds to deny it further benefit because
it has already been "given a break".  Is the 94 UBC a baseline of sorts that
future codes should be measured against?  There is no reason that code loads
should move in only one direction (higher) if research is able to justify a
reduction in some cases.  In this case, very long period buildings seem to
be pushing the limits of the research (hard to do full scale testing) and it
appears that there is a difference of opinion in some quarters.  Looking at
the IBC 2000 a bit, I have discovered some cases where (depending on the
soil) buildings will be treated even more favorably by the IBC than by the
97 UBC.  Is this unconservative?  As far as I can tell it is just different.
I suspect considerable discussion similar to this will occur if it is ever
adopted.  I have already seen one instance where its use was requested then
dismissed because it was "unconservative" for a particular case.  

Paul Crocker



"Take a moment and make a simple calculation of what this means to a
building with a 3 second or longer period, and you will realize that the 97
UBC has already given these buildings a big break in the lateral force used
to check drift requirements.  Despite the complaints of some
engineers that the code requirement was unfair, they were already getting a
break."