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Add New Time History Definitions dialog

Used to define the Forcing Function of a time varying load.

Opens when the Time History > Forcing Fucntions tool is selected in the Dynamic Specifications group on the Loading ribbon tab.

Note: Refer to TR.31.4 Definition of Time History Load for additional information.
Note: After defining a Time History Load, use the Create New Load Items dialog Time History tab to apply the load to the structure.
Integration Time Step Solution time step used in the step-by-step integration of the uncoupled equations.
Consider Missing Mass Mode Check this option to include the missing mass procedure in the time history analysis.

This refers to the number of the type of functions.

Loading Type Select the Acceleration, Force, or Moment option to define the type of function being input.
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.

The following function type options are available:

Select the Define Time vs. Acceleration, Harmonic Function or From External File option and provide function data.

Define Time vs. <Loading Type>

Used to specify a time history forcing function, where the loading type is that selected above (either Moment, Force, or Acceleration). 

Specify the values Time and corresponding Force or Acceleration

Note: The time history forcing function is plotted on the graph at the bottom of the dialog as data pairs are entered.

From External File

File Name

If the From External File option is selected, the File Name edit box becomes active. 

Type the name of the external file containing time history data.  File name should be no more than 8 characters, reside in the same directory as the current input and have no file extension.  The data must be provided as one time-force or time-acceleration pair per line. 

Note: For more information on creating an external time history file, see TR.31.4 Definition of Time History Load.

Harmonic Function

To specify a time history harmonic function, check the Harmonic Function button.

Curve Shape Specify if the harmonic function is a SINE or COSINE curve.
Frequency or RPM Choose Frequency and enter a circular frequency in cycles per second or RPM and enter revolutions per minute. 
Amplitude Max. Amplitude of the forcing function in current units.
Phase Phase Angle in degrees.
Cycles No. of cycles of loading.
Step or SubDiv Choose the Step option to time step of loading or SubDiv to subdivide a ¼ cycle into this many integer time steps.


Select this Function Option to provide Spectrum parameters for your time history loading.

Tmax The maximum time (in seconds) in the generated time history. Must be greater than T3.
DeltaT Difference (delta) value in subsequent time steps in the generated time history.
Damp Damping ratio (5% is entered as 0.05) associated with the input spectrum.
T1 / T2 / T3 Ending time of the acceleration rise, stead acceleration, and acceleration decay, respectively (in seconds).
Note: The value of T1 must be greater than zero. Further, T3 > T2 > T1 and Tmax must be greater than T3.
Random Seed Enter a positive integer (1 to 2,147,483,647) to be used as a unique random number generation "seed." A unique time history will be produced for each seed value. Change this value when you want to produce a "different (from the time history generated with the prior seed value)" but statistically equivalent time history.
No of digitized Freq. The input shock spectrum will be re-digitized at this number of equally spaced frequencies by interpolation. The default is taken as the greater of 35 or the number of points in the input spectrum.
No. of Iteration The number of iterations which will be used to perfect the computed time history.