which software is most suitable for me to analyst the building structure under seismic load?

Answer 1

It depends upon the location, type of construction, proportions of the building, and the building code requirements.
California and Alaska have some very stringent requirements that would not apply in other areas.
I would suggest that you Google "seismic building load analysis" or something similar and see what you come up with.
Most programs that deal with seismic analysis are relatively expensive.