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 comb-method *{ 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)
SPECTRUM
through
SCALE
above must be on the first line of the command,
the remaining data can be on the first or subsequent lines with all but last
ending with a hyphen (limit of four lines per spectrum).
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/sec2 units. This input is the appropriate value of acceleration due to gravity in the current unit system (thus, 9.81 m/s2 or 32.2 ft/s2). |
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 Massmethod to include the static effect of the masses not represented in the modes. The spectral acceleration length/sec2 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. Note: If the
MISSING parameter is entered on any spectrum case it will be used for all spectrum cases. |
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 4-98 standard in Hz units. For
ASCE option only.
|
FF2 f9 | 33 [Hz] | The f2 parameter defined in the
ASCE 4-98 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). The dominant mode is selected based on the actual base
shear of the mode and not the greatest % participation factor. Note: Do not enter the
SIGN parameter with this option. Ignored
for the ABS method of combining spectral
responses from each mode. |
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.
|
comb-method =
{ SRSS | ABS | CQC | ASCE | TEN | CSM | GRP }
are methods of
combining the responses from each mode into a total response.
The CQC and ASCE4-98 methods require damping. ABS, SRSS, CRM, GRP, and TEN methods do not use damping unless spectra-period 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.
Resultants are calculated as:Note: The cross-modal coefficient array is symmetric and all terms are positive.
- ASCE
- NRC Regulatory Guide Rev. 2 (2006) Gupta method for modal combinations and Rigid/Periodic parts of modes are used. The ASCE4-98 definitions are used where there is no conflict. ASCE4-98 Eq. 3.2-21 (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
orDISPLACEMENT
-
indicates whether Acceleration or Displacement spectra will be entered. The relationship between acceleration and displacement values in response spectra data is:
-
DAMP
,MDAMP
, andCDAMP
- 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 theDEFINE 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 theCONSTANT
specification
-
-
LINEAR
orLOGARITHMIC
-
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 Log-Log 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.Note: The last interpolation parameter entered on the last of all of the spectrum cases will be used for all spectrum cases. -
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/sec2. 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.Caution: Do not enterDOMINANT
parameter with this option.
-
p1, v1; p2, v2; …. ; pn, vn.
Data is part of input, immediately following theSPECTRUM
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/sec2) 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 theFILE 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 X-DIRECTION
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 X-DIRECTION
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 Y-DIRECTION
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 semi-colons. Multiple values may be entered per line.
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