Additional form: Damping Conversion
Use the options on the Additional Material Damping form to specify damping.
Modal Damping -- Damping Ratio edit box. Enter a value for the damping ratio (0 < = r < 1) to be used during a Response Spectrum or Model Time-History load case.
Viscous Proportional Damping -- Mass Coefficient and Stiffness Coefficient edit boxes. Enter values for these parameters that will be used during a Direct Integration Time History load case.
Make Other Damping Similar buttons. Clicking this button displays the Damping Conversion form. Use that form to specify that the damping be converted at a specified Period (second) or Frequency (cycle/second). The program will then automatically calculate damping that would be similar for the various types of analysis. In this way, the "same" damping can be evaluated for different load cases.
After the additional material damping has been specified as part of the material property definition, the additional damping is applied to the model by assigning the material property definition to a selected frame(s)/tendon object or a slab, deck, or wall object(s).
Access the Additional Material Damping form as follows:
Method 1
Click the Define menu > Material Properties command to display the Define Materials form.
Then do one of the following to access the Material Property Data form:
Click the Add New Material button to access the Add New Material Property form; specify a new property definition.
Highlight an existing definition and click the Add Copy of Material or Modify/Show Material button.
Click the Material Damping Properties button.
Method 2:
Click the 
button on the Frame Section Property Data form to bring up the Define Materials form.
Click the Add New Material button, which will bring up the Add New Material Property form. Use it to specify a material. The Material Property Data form will then display automatically.
Click the Material Damping Properties button.