TR.32.10.1.1 Response Spectrum Specification  Custom
This command may be used to specify and apply a custom (i.e., "generic" method) RESPONSE SPECTRUM loading for dynamic analysis.
This command should appear as part of a loading specification. If it is the first occurrence, it should be accompanied by the load data to be used for frequency and mode shape calculations. Additional occurrences need no additional information. The maximum number of response spectrum load cases allowed in one run is 50.
Results of frequency and mode shape calculations may vary significantly depending upon the mass modeling. All masses that are capable of moving should be modeled as loads, applied in all possible directions of movement. For dynamic mass modeling, refer to TR.32 Loading Specifications and G.17.3 Dynamic Analysis. An illustration of mass modeling is available, with explanatory comments, in Example Problem No.11.
General Format
SPECTRUM combmethod *{ X f1  Y f2  Z f3 } { ACCELERATION  DISPLACEMENT } (SCALE f4)
{DAMP f5  CDAMP  MDAMP } ( { LINEAR  LOGARITHMIC } ) (MISSING f6) (ZPA f7) (FF1 f8) (FF2 f9) ( { DOMINANT f10  SIGN } ) (SAVE) (IMR f11) (STARTCASE f12)
Starting on the next line, enter Spectra in one of these two input forms (i.e., explicit values or an external file):
{ p1 v1; p2 v2; p3 v3; …  FILE filename }
Where:
Parameter  Default Value  Description 

X f1, Y f2, Z f3  0.0  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. 
SCALE f4  1.0  Linear scale factor by which the spectra data will be multiplied. Usually used to factor g’s to length/sec^{2} units. This input is the appropriate value of acceleration due to gravity in the current unit system (thus, 9.81 m/s^{2} or 32.2 ft/s^{2}). 
DAMP f5  0.05 
The damping ratio.
Specify a value of exactly 0.0000011 to ignore damping.

MISSING f6  0 
Optional parameter to use the "Missing Mass" method to include the static
effect of the masses not represented in the modes. The spectral acceleration
length/sec^{2} for this missing mass mode is the f6 value entered in
length per second squared units (this value is not multiplied by
SCALE). If f6 is zero, then the spectral
acceleration at the
ZPA f7 frequency is used. If f7 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.
For SRSS, CQC, and TEN the results of this calculation are SRSSed with the modal combination results. For ABS, missing mass is ignored. For ASCE, the missing mass result is algebraically added with the rigid parts of the extracted modes. For ASCE, the MIS option is assumed to be on. If any of f6, f7, f8, or f9 are not entered, the defaults will be used. Missing mass does not include the effect of masses lumped at the supports unless the support is a stiff spring or an Enforced support. 
ZPA f7  33 [Hz]  The zero period acceleration value for use with MISSING option only. Defaults to 33 Hz if not entered. The value is printed but not used if MISSING f6 is entered. 
FF1 f8  2 [Hz]  The f1 parameter defined in the ASCE 498 standard in Hz units. For ASCE option only. 
FF2 f9  33 [Hz]  The f2 parameter defined in the ASCE 498 standard in Hz units. For ASCE option only. 
DOMINANT f10  1 (1st Mode)  The dominant mode method. All results will have the same sign as mode number f10 alone would have if it were excited then the scaled results were used as a static displacements result. Defaults to mode 1 if no value entered. If a 0 value entered, then the mode with the greatest % participation in the excitation direction will be used (only one direction factor may be nonzero). 
IMR f11  1  The number of individual modal responses (scaled modes) to be copied into load cases. Defaults to one. If greater than the actual number of modes extracted (NM), then it will be reset to NM. Modes one through f11 will be used. Missing Mass modes are not output. 
STARTCASE f12  Highest Load Case No. + 1  The primary load case number of mode 1 in the IMR parameter. Defaults to the highest load case number used so far plus one. If f12 is not higher than all prior load case numbers, then the default will be used. For modes 2 through NM, the load case number is the prior case number plus one. 
combmethod = { SRSS  ABS  CQC  ASCE  TEN  CSM  GRP } are methods of combining the responses from each mode into a total response.
The CQC and ASCE498 methods require damping. ABS, SRSS, CRM, GRP, and TEN methods do not use damping unless spectraperiod curves are made a function of damping (see File option below). CQC, ASCE, CRM, GRP, and TEN include the effect of response magnification due to closely spaced modal frequencies. ASCE includes more algebraic summation of higher modes. ASCE and CQC are more sophisticated and realistic methods and are recommended.
 SRSS
 Square Root of Summation of Squares method.
 ABS
 Absolute sum. This method is very conservative and represents a worst case combination.
 CQC
 Complete Quadratic Combination method (Default). This method is recommended for closely spaced modes instead of SRSS.
 ASCE
 NRC Regulatory Guide Rev. 2 (2006) Gupta method for modal combinations and Rigid/Periodic parts of modes are used. The ASCE498 definitions are used where there is no conflict. ASCE498 Eq. 3.221 (modified Rosenblueth) is used for close mode interaction of the damped periodic portion of the modes.
 TEN
 Ten Percent Method of combining closely spaced modes. NRC Reg. Guide 1.92 (Rev. 1.2.2, 1976).
 CSM
 Closely Spaced Method as per IS:1893 (Part 1)2002 procedures.
 GRP
 Closely Spaced Modes Grouping Method. NRC Reg. Guide 1.92 (Rev. 1.2.1, 1976).
 ACCELERATION or DISPLACEMENT
 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 or LOGARITHMIC
 Select Linear or Logarithmic interpolation of the
input Spectra versus Period curves for determining the spectra value for a mode
given its period. Linear is the default. Since Spectra versus Period curves are often
linear only on LogLog scales, the logarithmic interpolation is recommended in
such cases; especially if only a few points are entered in the spectra curve.
When FILE filename is entered, the interpolation along the damping axis will be linear.
 SAVE
 This option results in the creation of a acceleration data file (with the model file name and an .acc file extension) containing the joint accelerations in g’s and radians/sec^{2}. These files are plain text and may be opened and viewed with any text editor (e.g., Notepad).
 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. This command is ignored for ABS option.
 p1, v1; p2, v2; …. ; pn, vn. Data is part of input, immediately following the SPECTRUM command. Period – Value pairs (separated by semi colons) are entered to describe the Spectrum curve. Period is in seconds and the corresponding Value is either acceleration (current length unit/sec^{2}) or displacement (current length unit) depending on the ACC or DIS chosen. Continue the curve data onto as many lines as needed (up to 500 spectrum pairs). Spectrum pairs must be in ascending order of period. Note, if data is in g acceleration units, then set SCALE to a conversion factor to the current length unit (9.81, 386.4, etc.). Also note, do not end these lines with a hyphen (). Each SPECTRUM command must be followed by Spectra data if this input form is used.

FILE filename data is in a separate file, using the format described in File Format for Spectra Data.
When the File filename command has been provided, then you must have the spectra curve data on a file named filename prior to starting the analysis. The format of the FILE spectra data allows spectra as a function of damping as well as period.
Note: If the FILE filename command is entered, it must be with the first spectrum case and will be used for all spectrum cases.No File filename command needs to be entered with the remaining spectrum cases. The filename may not be more than 72 characters in length.
Examples
An example using joint loads and the SRSS combination method:
LOAD 2 SPECTRUM IN XDIRECTION SELFWEIGHT X 1.0 SELFWEIGHT Y 1.0 SELFWEIGHT Z 1.0 JOINT LOAD 10 FX 17.5 10 FY 17.5 10 FZ 17.5 SPECTRUM SRSS X 1.0 ACC SCALE 32.2 0.20 0.2 ; 0.40 0.25 ; 0.60 0.35 ; 0.80 0.43 ; 1.0 0.47 1.2 0.5 ; 1.4 0.65 ; 1.6 0.67 ; 1.8 0.55 ; 2.0 0.43
An example using member loads and the CQC combination method:
LOAD 2 SEISMIC LOADING SELFWEIGHT X 1.0 SELFWEIGHT Y 1.0 MEMBER LOADS 5 CON GX 5.0 6.0 5 CON GY 5.0 6.0 5 CON GX 7.5 10.0 5 CON GY 7.5 10.0 5 CON GX 5.0 14.0 5 CON GY 5.0 14.0 SPECTRUM CQC X 1.0 ACC DAMP 0.05 SCALE 32.2 0.03 1.00 ; 0.05 1.35 0.1 1.95 ; 0.2 2.80 0.5 2.80 ; 1.0 1.60
Multiple Response Spectra
If there is more than one response spectrum defined in the input file, the load data (representing the dynamic weight) should accompany the first set of spectrum data only. In the subsequent load cases, only the spectra should be defined. See example below.
LOAD 1 SPECTRUM IN XDIRECTION SELFWEIGHT X 1.0 SELFWEIGHT Y 1.0 SELFWEIGHT Z 1.0 JOINT LOAD 10 FX 17.5 10 FY 17.5 10 FZ 17.5 SPECTRUM SRSS X 1.0 ACC SCALE 32.2 IMR 2 STARTCASE 11 0.20 0.2 ; 0.40 0.25 ; 0.60 0.35 ; 0.80 0.43 ; 1.0 0.47 1.2 0.5 ; 1.4 0.65 ; 1.6 0.67 ; 1.8 0.55 ; 2.0 0.43 PERFORM ANALYSIS CHANGE * LOAD 2 SPECTRUM IN YDIRECTION SPECTRUM SRSS Y 1.0 ACC SCALE 32.2 0.20 0.1 ; 0.40 0.15 ; 0.60 0.33 ; 0.80 0.45 ; 1.00 0.48 1.20 0.51 ; 1.4 0.63 ; 1.6 0.67 ; 1.8 0.54 ; 2.0 0.42
File Format for Spectra Data
The format of the FILE spectra data allows spectra as a function of damping as well as period. The format is:
Dataset 1 MDAMPCV NPOINTCV (no of values = 2) Dataset 2 Damping Values in ascending order (no of values = Mdampcv) Dataset 3a Periods (no of values = Npointcv) 3b Spectra (no of values = Npointcv)
For ASCE, the MIS option is assumed to be on. If any of f6, f7, f8, f9 are not entered the defaults will be used.
Repeat Data set 3 Mdampcv times (3a,3b , 3a,3b , 3a,3b , etc.) (i.e., for each damping value).
Data sets 2, 3a and 3b must have exactly Npointcv values each. Blanks or commas separate the values. The data may extend to several lines. Do not end lines with a hyphen (). No comment lines (*) or semicolons. Multiple values may be entered per line.
where=  
= 
Examples of Spectra Data files
An example of spectral data for use in the X direction:
1,10 0.05 0.20 0.2 0.40 0.25 0.60 0.35 0.80 0.43 1.0 0.47 1.2 0.5 1.4 0.65 1.6 0.67 1.8 0.55 2.0 0.43
An example of spectral data for use in the Z direction:
1 10 0.05 0.20 0.40 0.60 0.80 1.0 1.2 1.4 1.6 1.8 2.0 0.1 0.15 0.33 0.45 0.48 0.51 0.63 0.67 0.54 0.42
Individual Modal Response Case Generation
Individual modal response (IMR) cases are simply the mode shape scaled to the magnitude that the mode has in this spectrum analysis case before it is combined with other modes. If the IMR parameter is entered, then STAAD.Pro will create load cases for the first specified number of modes for this response spectrum case (i.e., if five is specified then five load cases are generated, one for each of the first five modes). Each case will be created in a form like any other primary load case.
The results from an IMR case can be viewed graphically or through the print facilities. Each mode can therefore be assessed as to its significance to the results in various portions of the structure. Perhaps one or two modes could be used to design one area/floor and others elsewhere.
You can use subsequent load cases with TR.32.11 Repeat Load Specification combinations of these scaled modes and the static live and dead loads to form results that are all with internally consistent signs (unlike the usual response spectrum solutions). The modal applied loads vector will be omega squared times mass times the scaled mode shape. Reactions will be applied loads minus stiffness matrix times the scaled mode shape.
With the Repeat Load capability, you can combine the modal applied loads vector with the static loadings and solve statically with PDelta or tension only.