TR.32.10.1.10 Response Spectrum Specification per IBC 2006
General Format
SPECTRUM comb-method IBC 2006 *{ X f1| Y f2| Z f3} ACCELERATION
{DAMP f5| CDAMP | MDAMP } ( { LINEAR | LOGARITHMIC } ) (MISSING f6) (ZPA f7) ({ DOMINANT f10 | SIGN }) (SAVE) (IMR f11) (STARTCASE f12)
The command is completed with the following data which must be started on a new line:
{ZIP f8| LAT f9 LONG f13| SS f14S1 f15} SITE CLASS (f16) (FA f17 FV f18) TL f19
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. |
DAMP f5 | 0.05 |
The damping ratio.
Specify a value of exactly 0.0000011 to ignore damping.
|
MISSING f6 |
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/sec2 (this value is not multiplied by SCALE). If f6is zero, then the spectral acceleration at the ZPA f7frequency is used. If f7is zero or not entered, the spectral acceleration at 33Hz (Zero Period Acceleration, ZPA) is used. The results of this calculation are SRSSed with the modal combination results. |
|
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. |
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. |
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. |
ZIP f8 | The zip code of the site location to determine the latitude and longitude and consequently the Ss and S1 factors. (IBC 2006, ASCE 7-02 Chapter 22) | |
LAT f9 | The latitude of the site used with the longitude to determine the Ss and S1 factors. (IBC 2006, ASCE 7-02 Chapter 22) | |
LONG f13 | The longitude of the site used with the latitude to determine the Ss and S1 factors. (IBC 2006, ASCE 7-02 Chapter 22) | |
SS f14 | Mapped MCE for 0.2s spectral response acceleration. (IBC 2006, ASCE 7-02 Chapter 22) | |
S1 f15 | Mapped spectral acceleration for a 1-second period. (IBC 2000, equation 16-17. IBC 2003, ASCE 7-02 section 9.4.1.2.4-2. IBC 2006, ASCE 7-05 Section 11.4.1) | |
SITE CLASS f16 | Enter A through F for the Site Class as defined in the IBC code. (IBC 2000, Section 1615.1.1 page 350. IBC 2003, Section 1615.1.1 page 322. IBC 2006 ASCE 7-05 Section 20.3) | |
FA f17 | Optional Short-Period site coefficient at 0.2s. Value must be provided if SCLASS set to F (i.e., 6). (IBC 2006, ASCE 7-05 Section 11.4.3) | |
FV f18 | Optional Long-Period site coefficient at 1.0s. Value must be provided if SCLASS set to F (i.e., 6). (IBC 2006, ASCE 7-05 Section 11.4.3) | |
TL f19 | Long-Period transition period in seconds. (IBC 2006, ASCE 7-02 Chapter 22) |
IBC 2006 indicates that the spectrum should be calculated as defined in the IBC 2006 specification.
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.
- 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).
- ACCELERATOIN
- indicates that the Acceleration spectra will be entered.
- 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 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.
- 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.
- 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).
Methodology
The methodology for calculating the response spectra is defined in ASCE7-05, section 11.4. The following is a quick summary:
- Input Ss and S1 (this could have been searched from database or entered explicitly)
-
Calculate
Sms= Fa x Ss
and
Sm1 = Fv x S1
Where:
Fa and Fv are determined from the specified site classes A – E and using tables 11.4-1 and 11.4-2. For site class F, the values must be supplied. These are required to be provided by the user. You may also specify values for Fa and Fv in lieu of table values.
-
Calculate
Sds = (2/3) Sms
and
Sd1 = (2/3) Sm1
The spectrum is generated as per section 11.4.5.
See TR.32.10.1.1 Response Spectrum Specification - Custom for additional details on IMR load case generation.