Floor acceleration spectra, which are important for seismic design and assessment of accelerationsensitive equipment, were studied in the dissertation. A relatively simple practice-oriented method for the determination of floor acceleration spectra directly from the ground motion spectra was developed. Elastic and inelastic structural behaviour was taken into account. Extensive parametric studies were performed on single- (SDOF) and multi-degree-of-freedom (MDOF) structures and a large number of floor acceleration (response) spectra were calculated by using the response-history analysis (RHA). In the case of SDOF structures two different sets of ground records were used, whereas in the case of MDOF structures only one of these sets was considered. The influences of the type, natural period, hysteretic behaviour, and ductility of the primary structure, as well as the influence of the equipment damping, were studied. Additionally, in the case of SDOF structures, the influence of input ground motion characteristics was also investigated. The obtained results confirmed the fact that inelastic behaviour of the primary structure can significantly reduce floor acceleration spectra, especially their peak values. The method for direct determination of floor response spectra was firstly developed for SDOF structures and it was validated by comparing its results with the floor response spectra obtained from the RHA. A good agreement between the results obtained for both elastic and inelastic structural behaviour was observed. The method was extended to MDOF structures and it was coupled with the nonlinear pushover-based N2 method. In the case of elastic structures the method provides floor response spectra which are in very good agreement with the results obtained from the RHA. In the case of inelastic structures, in general, a satisfactory accuracy can be achieved.