TR.32.10.1.10 Response Spectrum Specification per IBC2006
RESPONSE SPECTRUM
loading as per the 2006 edition of the ICC specification International Building Code (IBC), for dynamic analysis. The graph of frequency – acceleration pairs are calculated based on the input requirements of the command and as defined in the code.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)
SPECTRUM
through ACC
must be on the first line of the command. The data shown on the second line above can be continued on the first line or one or more new lines with all but last ending with a hyphen (limit of four lines per spectrum). 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
If f6is zero, then the spectral acceleration at the
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.
|
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.
|
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.
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).
-
ACCELERATOIN
- indicates that the Acceleration spectra will be entered.
Note: IBC / ASCE 7 does not have provisions for displacement response spectra.
-
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. -
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. -
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 Ssand
Sm1 = Fv x S1Where:
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) Smsand
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.
Example
DEFINE REFERENCE LOADS
LOAD R1 LOADTYPE Mass TITLE REF LOAD CASE 1
JOINT LOAD
8 FX 49.035
3 6 FX 98.07
END DEFINE REFERENCE LOADS
…
LOAD 1 LOADTYPE Seismic TITLE RS_X
SPECTRUM SRSS IBC 2006 X 0.333 ACC DAMP 0.05 LIN
ZIP 92887 SITE CLASS E FA 0.900 FV 2.400 TL 8.000