Define Response Spectrum Functions

Form:  Define Response Spectrum Functions

Use the Define menu > Functions > Response Spectrum command to access the Define Response Spectrum Functions form and add, modify, or delete a response function from a text file, using code-specific parameters, or based on user specified parameters.

A response spectrum function is a list of period versus spectral acceleration values. In ETABS the acceleration values in the function are assumed to be normalized; that is, the functions themselves are not assumed to have units. Instead, the units are associated with a scale factor that multiplies the function and is specified when the response spectrum case is defined.

1. Click the Define menu > Functions > Response Spectrum command to access the Define Response Spectrum Functions form.

2. Use the Response Spectra display area, the drop-down list, and the buttons as appropriate to add, modify, or delete a response spectrum function. The Response Spectra display area lists all of the  response spectrum functions currently defined in the model file.

   • Add a New Function button. Choose the type of function from the "Choose Function Type to Add" drop-down list. Then click the Add New Function button. Use the hyperlinks below to access a function-specific Help topic.

1. 1. 1. • AS1170-2007

         • ASCE7-02

         • ASCE7-05

         • ASCE7-10

         • BOCA96

         • Chinese 2010

         • Eurocode8

         • Eurocode8-2004

         • From File

         • IS1893:2002

         • Italian NTC2008

         • Italian 3274

         • NBCC2005

         • NBCC2010

         • NBCC95

         • NEHRP97

         • NZS1170-2004

         • NZS4203

         • SP 14.13330.2014

         • Turkish EDP2007

         • UBC94 Spectrum

         •  UBC97 Spectrum

         •  User

Note: The following areas are common to the forms, and thus the topics accessed using the preceding hyperlinks, and are described here rather than repeated for each response spectrum function topic:

1. 1. • Function Name edit box. Use the default or specify a new name for the response spectrum function.

      • Function Damping Ratio edit box . Use the default or specify the damping ratio that will be used to generate the response spectrum curve. During analysis, the response spectrum curve will be automatically adjusted from this value to the actual damping present in the model.

      • Defined Function / Function Points. This area displays the period and spectral acceleration values for the function. They cannot be edited and are provided for review purposes only. These values update when changes are made to the response spectrum-specific parameters identified in the hyperlinked topics (above).  If manual changes to the Period and Acceleration values are necessary, click the Convert to User-Defined button to convert the function to a user-defined function, which will make the values editable.  

      • Function Graph area. The function graph area displays a graph of the function. It updates automatically the spectrum parameters are defined. Run the mouse pointer over the function graph and a dot appears along the line representing the response spectrum. The coordinates of the dot are reported in the box just below the graph. Use the Plot Options to review the display of the function graph.

      • Display Graph button. Some form will have this button. Click it to update the Function Graph if the graph does not automatically update as changes are made to the parameters.

1. • Modify or Show a Response Spectrum Function Definition

   • 1. Highlight the name of the function to be modified/shown in the Response Spectra area of the form.

     2. Click on the Modify/Show Spectrum button.

     3. The form that was used to define the function will appear. Use the form to make any changes or modifications. The hyperlinks provided above provide access to topics specific to each type of form.

   • Delete a Response Spectrum Definition

   1. 1. Highlight the name of the function to be deleted in the Response Spectra area of the form.

      2. Click the Delete Spectrum button.