United composite strength calculation method for special-shaped CFST columns with multiple cavities

Abstract

The present study investigates the method of calculating the composite strength of special-shaped concrete-filled steel tube (CFST) members with multiple cavities. Based on the research findings of CFST unified theory and some tests, a quantitative method to evaluate the concrete constraint effect is proposed for cross-sectional shapes ranging from regular triangles, squares…regular octagons to circles. The cross-sectional composite strength of regular polygonal CFST members is determined by the way dividing the concrete into effective and ineffective constraint regions, discounting constraint coefficients, and applying unified formulas. Additionally, a regression analysis is conducted to establish the relationship between interior angles and constraint effects. Subsequently, using quadrangle CFSTs as an example, this study investigates the relationship between cross-sectional regularity and constraint effect, and proposes a composite strength calculation method related to it. Finally, the special-shaped multi cavity cross section is separated into several simple polygonal cross sections, taking into account shape efficiency and regularity, to calculate the composite strength of each cavity CFST member and summarize them for determining the total axial compressive bearing capacity. The research findings indicate that a linear relationship exists between the interior angle of the cross section and the initial tangent line angle of the second-degree curve, which serves as the boundary between effective and ineffective constraint regions in regular polygonal steel tube confined concrete. The proposed unified composite strength calculation method, specifically designed for special-shaped CFST columns with multiple cavities, can accurately predict their actual strength.