Simulation of uniaxially compressed square ultra-high-strength concrete-filled steel tubular slender beam-columns

Abstract The application of ultra-high-strength concrete in a concrete-filled steel tubular (CFST) column is an emerging topic recognizing the greater member capacities and stiffness of high strength concrete. The current designing codes for composite structures have restricted the use of ultra-high-strength concrete. This is because very little research has been conducted on the structural response of eccentrically loaded square ultra-high-strength CFST slender beam-columns. Set against this limited research, a numerical model implementing the fiber element formulation has been developed in this paper to fill the knowledge gap on the behavior of square ultra-high-strength CFST slender beam-columns under combined compression-bending conditions. The fiber-based model accounts for important features including local and global interaction buckling, triaxial confinement mechanism, member imperfection, and geometric and material nonlinearities. The stress–strain relationships for normal- and high-strength concrete do not reflect completely the brittleness of ultra-high-strength concrete in the post-peak branch. The existing material model is modified for simulating the material response of ultra-high-strength concrete. A comparison is made between the experimental data and the numerical simulation to assess the accuracy of the fiber-based model. The model has shown to provide a good agreement between the test data and the simulation. The parametric investigation indicates that the ultra-high-strength concrete may be effectively and hence more economically used in short and intermediate steel–concrete composite columns subjected to the compression load with a small eccentricity. It is also noted that the steel section with yield stress up to 550 MPa can be utilized with the ultra-high-strength concrete. The design code, Eurocode 4, accurately predicts the bending strength of ultra-high-strength square CFST slender beam-columns subjected to uniaxial bending.