[PERSON]  
2 Department of Life Safety and Environmental Protection, Faculty of Life Safety and Environmental Engineering, Don State Technical University, Gagarin, 1, 344003 Rostov-on-Don, Russia; reception@donstu. columns contribute to the separation of axial forces and increase the structure's rigidity, load-bearing capacity, and plasticity. In addition, installing internal diaphragms inside the columns can significantly increase the ultimate load-bearing capacity and energy dissipation. Since high-strength materials are increasingly used in construction, an extensive experimental database has been developed in [7], for square and rectangular columns. Although the results showed that the existing regulatory framework is not effective for high-strength materials, the flexibility of square and rectangular columns can be safely reduced. Axial compression tests were carried out in [8] on rectangular concrete-filled steel pipe columns under various loading methods. In [9], the authors experimentally investigated 17 rectangular CFST columns subjected to eccentric loading on uniaxial and biaxial bending. The influence of the limiting factor and the eccentric ratio on the strength and ductility of the samples was investigated. The assessment of the stress-strain state of hexagonal steel columns filled with concrete was carried out in [10; 11; 12] by the finite element method. The columns were subjected to axial compressive forces and cyclic bending moments. Based on the FEM model, the authors determined the hysteresis characteristics of the columns, the contact stress between the steel pipe and concrete, and the contribution of the strength of various components over the entire load range. In [13], the authors note that concrete-filled tubular steel columns with rounded ends have the same advantages as regular CFST columns. 3D finite element models for columns are developed using ABAQUS software. Numerical results show that brittle fracture is associated with columns formed from outer thin steel cross-sections. Experimental and numerical studies of the structural characteristics of cold-formed high-strength steel octagonal tubular columns filled with concrete are presented in [14]. The authors studied ultimate loads, load-displacement reactions, and structural failure modes experimentally and numerically. The specifics of calculating the strength of short, centrally compressed concrete, steel pipe columns of the annular cross-section are considered in [15; 16]. In addition, the complex stress state of the concrete core and the steel shell and the uneven distribution of transverse stresses over the cross-section of the design elements are taken into account. Except for steel, fiberglass can be used as the shell material [17]. Unfortunately, most of the publications on the methods of calculating tube-shaped concrete, including those listed above, are based on an empirical approach that does not fully reflect the specifics of changes in the stress-strain state of columns under various loads. This imposes restrictions on the cross-sectional shape, shell material, and concrete composition (heavy and lightweight concrete, high strength concrete, regular concrete, etc.). Experimental studies of the stress-strain state of elliptical and oval columns made of concrete tubes subjected to axial compressive load were carried out in [18; 19]. Various column lengths, cross-sectional sizes, and concrete strengths are used to quantify the effect of element geometry and constituent material properties on the structural behavior of CFST elliptical columns. Experimental and numerical studies of the steel tubular column filled with concrete with an unequal wall thickness under eccentric compression were performed in [20]. The series of compression tests were performed on rectangular CFST columns with varying flexibilities, eccentricities, and wall thicknesses. The test results show that a rectangular CFST column with unequal wall thickness has higher ductility after peak load than a column with the same wall thickness with the same configuration.