[en] It is general practice to use the floor response spectra as input for seismic resistant design of safety class equipment of nuclear power plants. However, it is assumed that the equipment is very small in comparison with the supporting structure, in the generation of floor response spectra; hence, when the equipment becomes heavier and heavier, this method becomes unnecessarily conservative. Methods of seismic resistant design for heavy equipment as reactor vessels, steam generators, pumps, pressurizers, polar cranes, and ice condensers are discussed by combined analysis. The effect of resonance is also discussed in detail. (Author)