The article is devoted to increasing the level of seismic resistance of power facilities during their construction in areas with high seismicity. The object of the research is a system of double seismic isolation of the turbine foundation, the subject of the research is optimization of the lower seismic insulating layer parameters by varying the number of viscous dampers. The purpose of the research was to determine and calculate the optimal number of viscous dampers that provide the greatest reduction of maximum seismic axial accelerations at the turbine installation level under the high-frequency and the low-frequency seismic impacts. The main research method is conducting computational experiments: dynamic calculations are carried out in Nastran software package by time history analysis using the finite element method. The main criterion of seismic resistance of the vibration-isolated turbine foundation is the value of the maximum seismic axial accelerations at the turbine installation level. As a result of computational experiments, it was found that the greatest reduction of maximum axial accelerations under the low-frequency seismic impact is achieved by installing 160 dampers (40% of critical damping). Under the high-frequency seismic impact, 60 dampers are required (15% of critical damping). The final number of dampers in the seismic isolation layer of the turbine building for each project should be determined from a series of variant calculations that take into account many factors. The results of the research can be used for designing and calculating justifications for seismic isolation systems of perspective energy facilities such as the thermal power plants and the nuclear power plants.

Seismic isolation is the most effective way to achieve seismic resistance of buildings and structures, the equipment located inside. The energy center of any power plant is its turbine unit - the main equipment responsible for generating electricity. The seismic stability of the turbine unit is ensured primarily by the fulfillment of the seismic resistance criteria by the turbine unit foundation – a special building structure that combines the parts of the turbine unit into a single system and serves to take static and dynamic loads.

Achievement of seismic resistance of the turbine unit foundation of a power plant through the use of various seismic isolation systems is a topical issue discussed in this article.

Dynamic calculations were performed in Nastran software using time history analysis and the finite element method. The main criteria for the seismic resistance of a vibration-insulated turbine foundation are the values of the maximum seismic accelerations in the axial direction at the level of the turbine installation and the values of vibration-insulated foundation maximum seismic deformations of vibration isolators.

In the research, seismic calculations of the turbine unit foundation with various parameters of the double seismic isolation system of the turbine unit were performed. The results made it possible to evaluate the influence of the parameters of the turbine building spring-damper insulation on the seismic resistance of the vibration-insulated turbine unit foundation.

The turbogenerator set foundation is a special building structure that unites parts of the turbine and generator unit into a single system and it is used for static and dynamic loads accommodation. The number of designed and constructed power plants in high seismic level areas is large.

Seismic isolation is the most effective way to achieve earthquake resistance of equipment located inside buildings and structures. Achievement of seismic stability power plant turbine foundation by applying a variety of design solutions and seismic isolation systems is a significant issue.

Dynamic calculations were performed in Nastran software using time history analysis and the finite element method. The main criteria for the seismic resistance of a vibration-insulated turbine foundation are the values of the maximum seismic accelerations in the axial direction at the level of the turbine installation and the values of vibration-insulated foundation maximum seismicdeformations of vibration isolators.

The results of computational experiments during investigations allow to estimate the effect of the following factors on seismic resistance of vibration isolated turboset foundations:

- different frequency composition of seismic impact;

- use of vibration isolators of different stiffness;

- accounting of frequency dependence of viscous dampers characteristics;

- use of different calculation methods and computational models.