Introduction. The paper considers the stress-strain state of a steel frame with various seismic protection systems. The main purpose of numerical studies was to compare the ability of seismic loads to be dampened by various seismic protection systems and to determine the coefficient of allowable damage K₁ and excess strength Ω for a frame with eccentric braces. Since there is no such constructive system in SP14.13330.2018 when choosing the coefficient K₁, and there are no requirements for considering overstrength, this study will be a big step towards improving the standards for earthquake-resistant construction in our country.

Materials and methods. The study was performed in the SAP2000 software package, considering the physical and geometric nonlinearity. The work of a two-story steel frame with a span of 6 m and a floor height of 3 m with various seismic protection systems was considered. The earthquake was modeled using the 1940 El-Centro accelerogram. A system with a rigid beam-column assembly, a system with concentric braces, a system with eccentric braces, and seismic insulation in the form of rubber-metal supports (RMS) were considered seismic protection. The coefficients K₁ and Ω were calculated analytically based on results of FE-analysis.

Results. The ability to maximize the reduction of forces from the seismic impact of a frame with eccentric braces has been numerically proven, and the efforts in the elements during plasticization of the link (the beam section between the braces) reduce the forces in the elements by up to 76 % compared to other seismic protection systems. The permissible damage K₁=0.222 has been deduced for a frame with eccentric braces. The coefficients of overstrength Ω for frame elements with this type of seismic protection are also determined. For columns, Ω_col=3.47 for braces, Ω_brace=1.8 and for beams, Ω_beam=2.76.

Conclusions. This study has proved the significant superiority of seismic protection based on a system with eccentric braces compared to other systems that are the simplest to implement. The coefficient of permissible damage K₁ and the coefficient of excess strength Ω for this system were also derived. According to the calculation of the K₁ and Ω coefficients, it follows that due to plastic deformations in the brace, the forces in the structural elements are not proportionally reduced. Therefore, the introduction of only the K₁ coefficient, as dictated by SP 14.13330.2018, for calculating seismic impacts is extremely unacceptable, which can lead to the collapse of the structure.