Review article

Main features and methods of calculating nonlinear seismic isolation systems of buildings and structures are considered. The studies performed are based on numerical simulation of seismic vibrations of the structure modeled by a system with one degree of freedom. In this case, an exact solution of motion equations on the phase plane is used. To transfer the solution into the time domain, a cubic expansion of displacements in time is used. Research results show that for the majority of nonlinear seismic isolation systems there is no intrinsic period of oscillations of the system, the observed period depends on the amplitude and frequency of the perturbation. This makes it impossible to apply the linear-spectral methodology for calculating such systems, which is quite obvious, but is ignored by some specialists working in earthquake engineering. Another important consequence of the intrinsic period absence is the impossibility of classical resonant oscillation build-up of the system. At the same time, effects of an increase of the oscillation amplitude and the presence of several stable solutions under harmonic perturbation are possible at weak damping.