RESP, IR, LFTAB, LDTAB, specType, dampRatio, DTIME, TMIN, TMAX, inputType
Generates a response spectrum.
IRArbitrary reference number assigned to the response spectrum results (2 to NV [NUMVAR]). If this number is the same as for a previously defined variable, the previously defined variable will be overwritten with these results.
LFTABReference number of variable containing frequency table (created with FILLDATA or DATA command). The frequency table defines the number and frequency of oscillating systems used to determine the response spectrum. The frequency interval need not be constant over the entire range. Frequencies must be input in ascending order.
LDTABReference number of variable containing the input time-history.
specTypeDefines the type of response spectrum to be calculated:
0 or 1 | — | Displacement (relative to base excitation) |
2 | — | Velocity (relative to base excitation) |
3 | — | Acceleration response spectrum (absolute) |
4 | — | Pseudo-velocity |
5 | — | Pseudo-acceleration |
dampRatioRatio of viscous damping to critical damping (input as a decimal number).
DTIMEIntegration time step. This value should be equal
to or greater than the integration time step used in the initial transient
analysis performed to generate the input time-history (LDTAB).
DTIME defaults to a value of 1/(20*FMAX),
where FMAX is the highest frequency in the frequency table (LFTAB)
except when the time-history is read from the reduced displacement (RDSP)
file following a mode-superposition transient analysis without an expansion pass. In this
case, DTIME defaults to the time step value used in the analysis.
TMIN, TMAXSpecifies a subset of the displacement-time history to be used in the response spectrum calculation. Defaults to the full time range.
inputTypeDefines the type of the input time-history:
0 | — | Displacement (default) |
1 | — | Acceleration |
This command generates a response spectrum from a displacement or acceleration time-history and frequency data. The response spectrum is defined as the maximum response of single degree of freedom systems of varying frequency (or period) to a given input support excitation.
A response spectrum analysis (ANTYPE, SPECTR with SPOPT, SPRS or MPRS) requires a response spectrum input. This input can be determined from the response spectrum printout or display of this command.
If a response spectrum is to be calculated from a given displacement (or acceleration) time-history, the displacement time-history may be input to a single one-element reduced linear transient dynamic (ANTYPE,TRANS) analysis, so that the calculated output (which should be the same as the input) will be properly located on the file.
The integration time step (argument DTIME on the RESP command) and the damping coefficient
(argument dampRatio) are constant over
the frequency range. The number of calculations done per response
spectrum curve is the product of the number of input solution points
(TMAX-TMIN)/DTIME and the number of frequency points (frequencies
located in variable LFTAB).
Input solution points requested (using DTIME and the frequency range) at a time not corresponding to an actual
displacement solution time on the file are linearly interpolated with
respect to the existing points.
For the theory of the response spectrum calculation, see POST26 - Response Spectrum Generator (RESP).
For an example of the command usage, see Generating a Response Spectrum in the Basic Analysis Guide.