Abstract: Using Midas modeling, the lateral displacement of industrial columns with three different cross-section types, i.e., concrete-filled rectangular steel tube, concrete and H-shaped steel, was compared and calculated. The results show that concrete-filled steel tube column has significant advantages in increasing stiffness. Concrete-filled steel tube is a kind of composite material, and calculation formulas for equivalent stiffness from domestic and international specifications were listed based on the current theory of the superposition and reduction of composite material stiffness. Relevant domestic and international specifications consider the linear superposition and reduction of concrete and steel tubes in the calculation of the section stiffness of concrete-filled steel tube composite structures, and the reduction of concrete's stiffness takes into account the concrete cracking. In order to study the mutual constraints between concrete and steel tubes in practical applications, finite element analysis was carried out using Abaqus to model the interaction between steel and concrete in concrete-filled steel tube columns, and the stress-strain states of concrete-filled steel tube columns under different conditions such as compression and bending were compared. The analysis identified the parts of the structure that are prone to failure, providing a basis for calculation and design.

Key words: concrete-filled rectangular steel tube, stiffness reduction, composite structure, finite element analysis, instability failure