Free vibration after time history analysis

[alaa]

dear all
i ran the exapmle 5.1 (3drigidframe) and got the correct result. then as i think if i increase the time domain ( in this example 20sec) associated with
the earthquake record tapas. the model must go on free vibration
must be there is no response . so i increased the time to 30 sec. but i still have a response. like to be there is a time history record.
plz
anyone can explain that
Alaa

[fmk]

when e.q. ends the structure is subject to free vibration with the initial conditions being the response of the structure at the end of the e.q. .. how long you need to keep running for after the e.q. depends on the amount of damping present.