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Re: Quick/Easy Question for Seismic List

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> 17.76 inches is wrong. Your answer of 1.48 inches appears to be correct,
> although little less than I am used to see. (0.166%)
>
> The height used should be in feet not in inches. The formula uses feet. See
> then definition of the story height.

Why do you assume that if you put feet into the equation that it yields something
other than feet as its result?  It is also acceptable to use meters for story
height.  Surely this could not be so if the 0.02 was calibrated to make a feet to
inches conversion.  If the EERI web site still has the field report from the
earthquake in Columbia last year (?) posted, it might be worthwhile to read this,
as it briefly discussed observed correlations between drift and damage/failure,
which largely agreed with the pre-existing body of research.  Depending on your
anticipated loads and building use, getting too close to the 1.48' drift may not
be appropriate, but I do not see it as a code violation.  Also, if you get too
close to the drift limit, drift will exceed the threshold beyond which P-Delta
analysis cannot be ignored, which may cause problems of its own.  Overall,
though, if a maximum inelastic drift limit approach is taken, a limit of 1.48'
for a 74' building is not surprising.  Surely moment frames would never be
possible if a 1.48" level of stiffness was code required.  In fact, only the
longest shear walls could possibly comply with that.  Try to visualize 1.48" in a
74' building under extreme loading and imagine if that would be possible.

Paul Crocker