To add a response spectrum definition containing code-specific loading parameters, use the following procedure.

1. On the Catalog ribbon tab, select the Add Response Spectrum tool in the Load Definitions group.
   
   The Response Spectrum Definition dialog opens.
2. Type a unique Name for the new seismic load definition.
3. Select the Code and Version to use from the respective drop-down lists.
4. Select the Spectrum Type to use. whether Acceleration or Displacement spectra will be entered. The relationship between acceleration and displacement values in response spectra data is:
5. Select the Interpolation Type to use. 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.
6. (Optional) Type a Scale value to use.
7. Check the Save option to create an acceleration data file when the analysis is performed.
8. (Optional) Select torsion options:
   1. Check the Use Torsion option to account for dynamic torsion, accidental torsion, or both.
   2. Type a value to use for the Dynamic Eccentricity. This factor is multiplied by the calculated distance between the center of rigidity and the center of mass perpendicular to the static seismic force in a global direction.
   3. Type a value to use for the Accidental Eccentricity. This factor is applied to the perpendicular width of the structure at a diaphragm level to determine a torsional eccentricity distance. This is typically 0.05 (5%) to 0.1 (10%), depending on the building code or region. This value can be positive (clockwise torsion) or negative (counter-clockwise torsion).
9. (Optional) Select the individual modal response options:
   1. Check the Generate IMR Results option to copy individual modal responses into load cases.
   2. Type the No. Modes to be generated. If greater than the actual number of modes extracted, then the actual number of modes will be used.
   3. To specify the starting load case number for the IMR results, check the Set Start Load Case option and then type the Load Case No to use as the first load case.
10. For US codes, select the Options to use for specifying mapped acceleration values:
    • Zip - postal codes
    • Latitude/Longitude - geo-coordinates
    • Ss/S1 - specify the acceleration values directly
11. Specify spectral values or code-specific parameters:

    Option	Description
    Custom, Canadian, or Indian (with custom subsoil)	Click in the Values field and type the Period and Acc/Disp data pairs.
    European, Indian, Russian, or US	Specify the code-specific parameters to define the response spectrum.

12. Click OK.