M. To define time history parameters
To define arrival times and damping used for time history loads, use the following procedure.

On the Loading ribbon tab, select the
The tool in the Dynamic Specifications group. Define Param dialog opens.  (Optional) Check the Time Step option and type the time step value. This is the solution time step used in stepbystep integration of the uncoupled equations. If not selected, the default value of 0.0013888 seconds is used.
 Select the Damping Type to use and, if explicit Damping is selected, type the damping ratio to be used for all modes.
 Type in one or more Arrival Times for the dynamic loads. Arrival time is the time at which a load type begins to act at a joint (forcing function) or at the base of the structure (ground motion).
 Click Add.