- The input spectrum type can be displacement, velocity, force, pressure, or acceleration. The type of
excitation (base excitation or a nodal excitation) is specified in steps 4 and 5 of this procedure. If a
pressure spectrum is to be applied, the pressures should be applied in the modal analysis.
- Spectrum value-versus-frequency table
Define the points of each spectrum curve. You can define a family of spectrum curves; each curve
is associated with a damping ratio.
Command(s):SPFREQ,SPVAL,SPDAMP,SPGRAPH
GUI: These commands can not be accessed from a menu.
You can issue STAT to list the tables and SPGRAPH to display them.
- Missing mass and rigid responses
- 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 exist
between the residual vector and the modes depending on the mode combination method.
A frequency is associated with the residual vector. The input spectrum for this frequency should
correspond to the Zero Period Acceleration value. The frequency is also used for the calculation
of the velocity and acceleration solutions.
- Apply the excitation.
- For base excitation, use the UX,UY,UZ and the ROTX,ROTY,ROTZ labels on the D (or DK, or DL, or
DA) command. A value of 0.0 (or blank) removes a specification. Values other than 1.0 scale the parti-
cipation factors.
- For uniform base motion using the SED command, specify SEDX,SEDY, or SEDZ. A value of 0.0 (or
blank) removes a specification.
- For nodal excitation, use the FX,FY,FZ on the F (or FK) command. A value of 0.0 (or blank) removes
a specification. Values other than 1.0 scale the participation factors.
Release 15.0 - © SAS IP, Inc. All rights reserved. - Contains proprietary and confidential information
Performing a Multi-Point Response Spectrum (MPRS) Analysis
