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Access the Response Spectrum Function Definition form as follows:
Click the Define menu > Functions > Response Spectrum command to display the Define Response Spectrum Functions form. Then do one of the following:
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Use the options on the Response Spectrum Function Definition form to complete the definition of a response spectrum function based on a text file of response spectrum data.
Function name edit box. Specifies the name of the function; use this edit box to modify the name if desired.
Function File area. Click the Browse button in this area to access the Pick Function Data File form; use the form to indicate the name of the text file that includes the response spectrum data. The name of the selected file will display in the File Name display box. Click the View File button to display the selected file in text format in WordPad.
The program reads the response-spectrum function file in the following way:
First, it skips the specified number of header lines (see Header Lines to Skip below).
Next, it checks to see if a line has a $ symbol as the first character. If it does, the program skips to the next line.
If the first character on the line is not a $ symbol, the program reads the information on the line.
If the line is blank or if the end of the file is reached, the program stops reading and closes the file.
Typically the program does not import the file into its database. It simply maintains a link to the file location. Thus, if either the response-spectrum file or the .SDB file is moved to another location, the program may suddenly be unable to locate the response spectrum file. If the Convert to User Defined button is clicked, the program imports the response spectrum into its database file and the data will always be available.
Important: Do not click the Convert to User Defined button until the file name and the number of header lines to skip have been specified.
Header Lines to Skip edit box. When reading the function file, the program skips the number of lines at the top of the file indicated in the Header Lines to Skip edit box.
Values are area. Choose whether the data in the file is given as Frequency vs. Value or Period vs. Value. This area will also display the values read from the file after the function is displayed in the Function graph area of the form. Internally the program will convert a function that is specified in terms of frequency into a function of period. All interpolation between data points is performed by period.
Function graph area. This area displays a graph of the function. First specify the text file name and the number of header lines to skip in the Function File area of the form. Then click the Display Graph button in the Function Graph area of the form to display the graph of the function. This also fills in the values in the Values are area of the form.
Run the mouse pointer over the function graph to display a dot along the line representing the response spectrum. The coordinates of the dot are reported in the box just below the graph.