Defining a spectrum

Use the spectrum method to define a spectrum to be used in a response spectrum analysis. For more information, see Specifying a Spectrum.

  1. Display the Edit Amplitude dialog box as described in Selecting an amplitude type to define.
  2. Click the arrow to the right of the Specification units field, and specify the units in which you want to define the spectrum.

    • Select Displacement, Velocity, or Acceleration to define the spectrum in displacement units, velocity units, or acceleration units, respectively.

    • Select Gravity to specify an acceleration spectrum in g-units.

  3. If you selected Gravity, enter the value of the acceleration of gravity.
  4. In the data table, enter the Magnitude (magnitude of the spectrum), Frequency (frequency, in cycles per time, at which this magnitude is used), and Damping (associated damping, given as a ratio of critical damping) values. For detailed information on how to enter data, see Entering tabular data.
  5. Click OK to save your amplitude definition and to close the Edit Amplitude dialog box.