TR.32.10.1.6 Response Spectrum Specification per GB 50011 2010
General Format
SPECTRUM { CQC  SRSS } GB50011 (2010) *{ X f1  Y f2 Z f3 } ALPHA
{DAMP f4  CDAMP  MDAMP } ( { LINEAR  LOGARITHMIC } ) (MISSING f5) ( ZPA f6 ) ({ DOMINANT f10 SIGN }) 
{ ( INTENSITY f9 ) ( FREQUENT  FORTIFIED  RARE ) ( GROUP f11 ) ( SCLASS f12 ) }
Where:
Parameter  Default Value  Description 

X f1, Y f2, Z f3    Factors for the input spectrum to be applied in X, Y, & Z
directions. Any one or all directions can be input. Directions not
provided will default to zero if the global axis is not specified.
If the direction is specified, then the default factor for X and Z is 1.0 where as the default factor for Y is 0.65. At least one direction must be specified. Any directions that is not specified will default to zero. 
DAMP f4  0.05 
The damping ratio.
Specify a value of exactly 0.0000011 to ignore damping.

MISSING f5 
Optional parameter to use "Missing Mass" method. The static effect of the masses not represented in the modes is included. The spectral acceleration for this missing mass mode is the f6value entered in length/sec^{2}. If the "missing mass" option is used, then this value must be provided. 

ZPA f6  33 (Hz)  The zeroperiod acceleration value used with the MISSING option only. 
DOMINANT f7  1 (1st Mode)  Dominant mode method. All results will have the same sign as mode number f7 alone would have if it were excited then the results were used as a static displacements result. Defaults to mode 1 if no value is entered. If a value of 0 is entered, then the mode with the greatest % participation in the excitation direction will be used (only 1 direction factor may be nonzero). 
INTENSITY f9  7  Fortification seismic intensity. Permitted values are: 6, 7, 7A, 8, 8A, or 9 
GROUP f10  2  Design seismic group. 
SCLASS f11  2  Site class. 
{ SRSS  CQC } are methods of combining the responses from each mode into a total response. The CQC methods requires damping. SRSS method do not use damping unless spectraperiod curves are made a function of damping. CQC includes the effect of response magnification due to closely spaced modal frequencies. CQC is a more sophisticated and realistic method and is recommended.
 SRSS
 Square Root of Summation of Squares method.
 CQC
 Complete Quadratic Combination method (Default). This method is recommended for closely spaced modes instead of SRSS.
 DAMP, MDAMP, and CDAMP
 select source of damping input:
 DAMP indicates to use the f2 value for all modes
 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
 CDAMP indicates to use the composite damping of the structure calculated for each mode. You must specify damping for different materials under the CONSTANT specification
 LINEAR  LOGARITHMIC
 Specifies the type of interpolation of the input seismic coefficient versus time period curves for determining the seismic coefficient value for a mode given its period. Linear is the default if not specified.
 SIGN
 This option results in the creation of signed values for all results. The sum of squares of positive values from the modes are compared to sum of squares of negative values from the modes. If the negative values are larger, the result is given a negative sign.
 FREQUENT  FORTIFIED  RARE
 The earthquake type.