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Re: Dynamic Analysis - STAAD III

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>Does this limitation imply that 
>the effect of mode frequencies higher than 60 cps are insignificant?
Yes.  

> If so, 
>is that assumption valid for all structures?
No. For seismic analysis there is no significant magnification of ground 
motion above 30-40 Hz (rule of thumb), but I've seen nuke plant response 
spectra with magnification up around 100 Hz because of some peculiarity 
in the plant. I haven't run into any, but there's no reason that some 
subsystem might not have significant response above 60 Hz which could be 
excited by ground motion.

Christopher Wright P.E.    |"They couldn't hit an elephant from
chrisw(--nospam--at)skypoint.com        | this distance"   (last words of Gen.
___________________________| John Sedgwick, Spotsylvania 1864)
http://www.skypoint.com/~chrisw