Inelastic analysis of octagonal concrete-filled steel tubular short columns under eccentric loading

Octagonal concrete-filled steel tubular (OCFST) columns combine the benefits of circular and square concrete-filled steel tubular (CFST) columns so that they not only possess higher strength and ductility but also provide the ease of connection to composite beams. However, research studies have been very limited on the performance analysis of OCFST short beam-columns subjected to eccentric loading. In this study, a fiber-based numerical model is developed for the performance simulation of high-strength OCFST short beam-columns under eccentric loading. The simulation model takes into account material nonlinearities and concrete confinement induced by the octagonal steel tube. Computational methods are given that predict the axial load-moment interaction curves and moment-curvature responses of OCFST beam-columns. The developed fiber model is verified against available test data with good accuracy. The influences of important parameters on the responses of high-strength OCFST short beam-columns are studied by means of utilizing the computational model. It is found that the behavior of OCFST beam-columns is significantly influenced by the diameter-to-thickness ratio of the cross-section, concrete strength, steel yield stress, and axial load ratio. Interaction equations are proposed for expressing the axial load-moment strength envelopes of the cross-sections of OCFST beam-columns and validated against numerical results.