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Direct integration time history cases are sensitive to time-step size, which should be decreased until results are not affected. Nonlinear direct integration time history cases can be load sequenced after either a nonlinear time history  case or after a nonlinear static case, and can account for nonlinear boundary conditions and nonlinear P-delta effects.

Comparison between FNA and direct-integration time-history analyses

Time history analysis may be initiated using the process which follows:

  1. Create the model and assign support conditions.

  2. Select Define > Functions > Time History to define a time-history function which characterizes load variation over time.

  3. Assign load conditions to the model.

  4. Define either a   modal  or direct-integration time-history load case through Define > Load Cases.

  5. Enter on the Load Case Data form under Loads Applied, the following fields:

    • Load Type. Select load pattern or specify an acceleration.
    • Load Name. Either load pattern name or acceleration direction
    • Function. Select the time history function which characterizes load variation in time. 
    • Scale Factor If acceleration load type apply scale factor as a percentage of G in current units

       6. On the left side of the time history load case dialogue under Properties, users will find options to specify load sequencing using the 'Continue from End state of' field, an option            to  to select a mass source, and option to specify P-delta if it's a nonlinear direct integration time history case, and time step data. Number of time steps X output step size should add up to a time frame which is at least as long as the time history function used in the time history case.