Option Command GUI Path
Main Menu> Solution> Load Step Opts> Time/Frequenc>
Damping
Beta (Stiffness) BETAD
Damping
Main Menu> Solution> Load Step Opts> Time/Frequenc>
Damping
Alpha (Mass) ALPHAD
Damping
Main Menu> Solution> Load Step Opts> Time/Frequenc>
Damping
Constant Damping DMPRAT
Ratio
Main Menu> Solution> Load Step Opts> Time/Frequenc>
Damping
Modal Damping MDAMP
These data include the following:
- Type of Response Spectrum [SVTYP]
The spectrum type can be displacement, velocity, acceleration, force, or PSD. All except
the force spectrum represent seismic spectra; that is, they are assumed to be specified at
the base. The force spectrum is specified at non-base nodes with the F or FK command,
and the direction is implied by labels FX, FY, FZ.The PSD spectrum [SVTYP,4] is internally
converted to a displacement response spectrum and is limited to flat, narrowband spectra;
a more robust random vibration analysis procedure is described in Performing a Random
Vibration (PSD) Analysis (p. 159).
- Excitation Direction [SED]
In addition, the ROCK command allows you to specify a rocking spectrum.
- Spectral-Value-Versus-Frequency Curve [FREQ,SV]
SV and FREQ commands are used to define the spectral curve with a maximum of 100
points. You can define a family of spectral curves, each curve for a different damping ratio.
Use the STAT command to list current spectrum curve values, and the SVPLOT command
to display the spectrum curves.
- Missing Mass Effect [MMASS]
The missing mass effect reduces the error caused when the higher modes are neglected
in the analysis.
- Rigid Responses Effect [RIGRESP]
If rigid responses are included, the combination of modal responses with frequencies in
the higher end of the spectrum frequency range will be more accurate.
Just like the missing mass response, the residual vectors reduce the error caused when
the higher modes are neglected in the analysis.
Unlike the missing mass response, the residual vector is calculated in the modal analysis
and is considered as an additional mode. Hence, it is combined as such, and coupling may
Release 15.0 - © SAS IP, Inc. All rights reserved. - Contains proprietary and confidential information
Single-Point Response Spectrum (SPRS) Analysis Process
