Numerical Analysis of Composite Steel-Concrete Columns of Arbitrary Cross Section

This paper presents a numerical formulation for the nonlinear analysis of slender steel-concrete composite columns of generic cross-sectional shape, subjected to axial force and biaxial bending. The cross section is defined in terms of a number of closed polygonal loops of a specific material, each one with its own stressstrain relation, with reinforcement bars embedded in the polygons. The material and geometrically nonlinear equlibrium problem is solved by the finite element method, with displacement-based stress resultant beam-column elements. The proposed scheme turns possible, with a unified treatment, to perform analyses of concrete-filled steel tubes, fully or partially encased steel profiles, or less usual cross sections present on composite construction. The robustness and accuracy of the formulation is verified against numerical and experimental results available in the literature.