Define Time History Function

Form:  Define Time History Functions

A time history function may be a list of time and function values or just a list of function values that are assumed to occur at equally spaced intervals. The function values in a time history function may be normalized ground acceleration values or they may be multipliers for specified (force or displacement) load patterns.

Note: By default, the program pre-defines a unit constant time-history function and a unit ramp time-history function. These may be modified or deleted.

Important: You may define a time-history function for any time range you want, t0 to tn. For all time before the first given time t0, the function value is assumed to be zero. At time t0, the function quickly ramps up to the first specified function value. For all time after the last given time tn, the function value remains constant at the last specified function value. Be sure to specify a final point with zero function value if you want the function to end at zero value. This is particularly important for acceleration records supplied in a file from other sources.

1. Click the Define menu > Functions > Time History Functions command to access the Define Time History Function form.

2. Use the following buttons to complete the appropriate action:

   • Add New Function button

   1. 1. Use the Choose the Function Type to Add drop-down list to select the type of function to be added.

      2. Click the Add Function button. This opens the appropriate form to enter the data needed to define the function. For more information, see:

1. • 1. • Function from File

        • {Type} Function

        • User Function

        • User Periodic Function

   • Modify/Show Function button

   • 1. Highlight the name of the function to be modified in the Functions display list.

     2. Click the Modify/Show button to access the same form as was used to define the function.

     3. Use the form to make the necessary changes. Note that a function from file or {type} function can be changed to a user defined function type. Topics describing the various function forms are accessible using the hyperlinks in the Add New Function button description, above, or by displaying the form and clicking the F1 key to access the Help topic specific to that form.

   • Delete Function button

   • 1. Highlight the name of the function to be deleted in the Functions display list.

     2. Click the Delete Function button.

Example:  Use of this command is demonstrated in Problem O and Problem Q.