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STAAD Commands and Input Instructions
Section 5
5-306
DAMP , CDAMP , MDAMP. Select source of damping input.
f4 = Damping ratio for all modes. Default value is 0.05 (5%
damping if 0 or blank entered).
DAMP indicates to use the f4 value for all modes.
CDAMP indicates to use Composite modal damping if entered,
otherwise same as MDAMP.
MDAMP indicates to use the damping entered or computed with
the DEFINE DAMP command if entered, otherwise default value
of 0.05 will be used.
LIN or LOG. Select linear or logarithmic interpolation of the
input Spectra versus Period curves for determining the spectra
value for a mode given its period. LIN is default. Since Spectra
versus Period curves are often linear only on Log-Log scales, the
logarithmic interpolation is recommended in such cases; especially
if only a few points are entered in the spectra curve.
For LIN or LOG , when FILE fn is entered, the interpolation
along the damping axis will be linear. The last LIN-LOG
parameter entered on all of the spectrum cases will be used for all
spectrum cases.
MIS f5 = Use Missing Mass method to include the static effect of
the masses not represented in the modes. The spectral acceleration
for this missing mass mode is the f5 value entered in length per
second squared units (this value is not multiplied by SCALE). If
f5 is zero, then the spectral acceleration at the ZPA f6 frequency is
used. If f6 is zero or not entered, then the spectral acceleration at
33Hz is used. The results of this calculation are SRSSed with the
modal combination results. If the MIS parameter is entered on any
spectrum case it will be used for all spectrum cases.
ZPA f6 = For use with MIS option only. Defaults to 33 Hz if not
entered. Value is printed but not used if MIS f5 is entered.
Save = The save option results in the creation of a file (file
name with "Acc" extension) containing the joint accelerations in
g’s and radians/sec
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