For the majority of buildings and structures, the analysis of seismic effects is performed employing the linear-spectral method, and is included into the design regulations of different countries. The linear-spectral analytical method allows for estimating the inelastic deformations in structures by reducing (decreasing) the actual seismic load by means of the coefficient of reduction. The current method of the seismic load reduction corresponds to the elastic-plastic type of structural deformation, with the coefficient of reduction applied to the load-bearing system as a whole. Nonetheless, this deformation pattern is not the only one available. There are structures and structural materials that trigger the elastic-brittle mechanism of transition to the limit state. The constructed buildings and facilities normally contain the structural elements of various deformation patterns (combined structural schemes), and that requires consideration when choosing the calculation method. Employing a universal coefficient of reduction in the design calculations of the combined structural schemes leads to an inaccurate result. Opposite to this, the authors propose herein a solution to the problem of accounting for the joint activity of elastic-plastic and elastic-brittle elements being part of the entire structure based on the energy method. Studied is the combined design model with a single degree of freedom and consisting of elements with different mechanisms of inelastic deformation. Various scenarios of conditions for the joint deformation of heterogeneous elements are analyzed. The general solution to the problem of the coefficient of reduction value for the load-bearing systems made of the elements of different types of inelastic deformation depends on the ratio of stiffness values of the elastic-plastic and elastic-brittle subsystems in structures, as well as on the ratio of bearing capacity of such subsystems. General solutions are obtained to the problem of the maximum permissible value of the coefficient of plasticity for the combined load-bearing system that is responsible for safety of the elastic-brittle sections in structures, and for the system as a whole. When employing the linear-spectral method to calculate the seismic effects for individual parts in structures, it is suggested to use differentiated coefficients of reduction, which is, in fact, complies with the actual performance pattern of structures.