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Re: Dynamic Analysis - STAAD III

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I am a student of structural analysis (not a experienced engineer) so my
answer is not very reliable. My opinion is that the contibution of each mode
results from two effects:
- participation factor (per mode) and spectral displacement.
The participation factors are much more important in first modes, because of
the coerence of the modal deformed shape, with all the parts involved in the
calcul of the participation factor adding. About the spectral displacement I
would need to know your country seismic spectra, but I can guess that it
never reaches 60 cps, so the displacement is very low for that frequency.

-----Original Message-----
From: RajSTC(--nospam--at) <RajSTC(--nospam--at)>
To: seaint(--nospam--at) <seaint(--nospam--at)>
Date: Quinta-feira, 13 de Abril de 2000 0:00
Subject: Dynamic Analysis - STAAD III

>In the dynamic analysis section of STAAD III, the response is computed on
>basis of contribution from mode frequencies less than 60 cps.  Any
>participation of higher modes are ignored. Does this limitation imply that
>the effect of mode frequencies higher than 60 cps are insignificant?  If
>is that assumption valid for all structures?
>P. Rajendran
>Service & Technology Corporation
>105 SW Penn
>Bartlesville, OK 74003
>Ph: 918 336 8161  FAX: 918 336 8265