The article is devoted to a newly developed complex finite element that allows modeling concrete-filled steel tubular columns taking into account the compression of the concrete core from the steel tube, as well as geometric nonlinearity. The derivation of the resolving equations, as well as expressions for the elements of the stiffness matrix, is based on the hypothesis of plane sections. The complex testing of the finite element was performed using the program code written by the authors in the MATLAB language and the ANSYS software, as well as the analysis of the effectiveness of the new FE in comparison with the classical methods of modeling CFST-columns in modern software systems. A significant decrease in the order of the system of FEM equations is demonstrated in comparison with the modeling of CFST-structures in a volumetric formulation in existing design complexes using SOLID elements for a concrete core with 3 degrees of freedom in each of the nodes, and SHELL elements for a steel tube with 6 degrees of freedom in each of the nodes, with a comparable accuracy in determining the stress-strain state. The behavior of steel and concrete in the presented work is assumed to be linearly elastic, however, the described calculation method can be generalized to the case of using nonlinear deformation models of materials.
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