Create: Time History load definition dialog

This dialog is used to specify the parameters for a time history loading on the structure. The time history data may be specified using either explicit definition or a function specification.

Opens when the Add Time History tool is selected on the Catalog ribbon tab in the Load Definitions group.

Note: Refer to the Options dialog Dynamic tab for additional settings that apply to all dynamic analysis and time history load cases.

Setting

Description

Load Definition

Setting	Description
Name	Type a unique name to identify the time history load definition.
Save	Select this option to create an external file (input file name with a .tmh extension ) containing the history of the displacements of every node of the structure at every time step.
Curve Type	Select the type of time history curve to use: Ground Motion (i.e., Acceleration) indicates that the time varying load type is a ground motion. Force indicates that it is a forcing function. Moment indicates that it is a moment forcing function.
Data point source	Select the method of input for the time history values: Custom – specify explicit data pairs for the selected Curve Type for specific times. External – specify explicit data pairs for the selected Curve Type for specific times using an external file. Polynomial - Uses a second-order polynomial (quadratic polynomial) to describe the time curve. Damped Harmonic – You will specify the factors in a generalized damped harmonic function. Harmonic – specify a harmonic function parametrically Tip: When entering parameters for polynomial or damped harmonic functions, any of the coefficients may be left as zero. However, time interval and finish time must be specified.

Custom source

Setting	Description
Acceleration / Force / Moment data	Click the drop-down field to display a table for entering explicit data point pairs. Type the time (in seconds) and the ordinate (i.e., acceleration, force, or moment depending on the Curve type selection) in the specified units. Tip: You can copy and paste data pairs for external data sources, such as a spreadsheet.

External source

Displayed when the Externaloption is selected as the Data point source.

Setting	Description
Browse	Click the folder icon to use a Windows Open dialog to select the external data file. Plain text files (file extension .txt) must be used. Note: Time history data files should have a file name no more than 72 characters long. The file path and file name must not contain spaces or hyphens (i.e., dashes).
Acceleration / Force / Moment data	Click to display the data pairs read from the external file.

Polynomial Function

Uses a second-order polynomial (quadratic polynomial) to describe the time curve. Define the polynomial coefficients, along with the time increment and finish time.

Tip: You can type in units to automatically convert values.

A + B t + C t^{2}

where:

Factor A: Constant shift
Factor B: First order (linear) factor
Factor C: Second order (quadratic) factor

Damped Harmonic Function

Uses a general form, harmonic function with exponential decay to describe the time curve. Define the function coefficients, along with the time increment and finish time.

Tip: You can type in units to automatically convert values.

A \times e^{- B (t - C)} \times [D \sin^{E (t - F)} + G \cos^{H (t - I)}] + J

where:

A: Coefficient for overall amplitude
B: Coefficient of decay rate
C: Decay time shift
D: Sine amplitude coefficient
E: Sine wavelength coefficient
F: Sine time shift
G: Cosine amplitude coefficient
H: Cosine wavelength coefficient
I: Cosine time shift
J: Constant shift

Note: The labels for the constants adjust to reflect the Curve Type selection.

Harmonic Function

Setting	Description
Function	Select the function type: SINE COSINE
Rotational Speed	Select how the rotational speed is specified: Frequency – specify the rotational Frequency in cycles/second. RPM – specify the revolutions per minute (RPM)
Amplitude
Has Phase	Check this option. Specify the Phase value.
Cycles
Time	Select how the time increments are specified: Step – SubDiv –

Time

(For Polynomial and Trigonometrical Functions only)

Setting	Description
Interval	The delta time spacing for use with generating discrete points for a function. The default value equals the Integration Time Step specified in the Options dialog.
Finish Time	The cutoff time used for the last point generated. A default of 20 s is given.

Note: When a function is used, an internal algorithm will calculate the peak points (i.e.,maxima and minima). Even if these do not fall on one of the intervals specified, peak points will be added to the table of points evaluated.