I have a project specifications review task for which I have a question regarding seismic drift limits for mill buildings with overhead bridge cranes. My associate insists that h/400 should be applied for the seismic drift limits, just as it would be for wind drift (measured at the crane rail elevation, per AIST TR-13). I say that an earthquake is an ultimate strength event, and this is too strict a limit. I believe that something more like h/60 is more appropriate. One isn't concerned with keeping a straight-tracking rail line during an earthquake. You only want to ensure that in addition to the building not collapsing, that the crane doesn't fall off the rails. This may take a lateral restraint or keeper to accomplish, but you still don't want to apply a limit that is too strict. What is the current thinking on this subject for mill buildings with heavy crane loads (100 tons, or more)?
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