Behaviour and design method of short square tubed-steel-reinforced-concrete columns under eccentric loading

The tubed-steel-reinforced-concrete (TSRC) column is a kind of special concrete-encased steel composite columns using the thin-walled steel tube instead of a reinforcement cage to confine the concrete core. The steel tube discontinues at the beam-column joints and thus does not carry any direct axial load. In this study, twelve short square TSRC columns were tested to investigate their load-carrying and deformation capacities under eccentric compression. The studied parameters are width-to-thickness ratio of the steel tube, eccentricity of the axial load, and the flange shear studs. The test results indicate that the encased steel shape works with the concrete compatibly due to the confinement from the steel tube, and the flange shear studs are not effective in enhancing the flexural stiffness and the axial resistance. To account for the inelastic behaviour of structural steel and concrete materials, a numerical model based on the fibre sectional analysis was developed, which predicts the results in general agreement with the test results. Parametric analysis is carried out based on the numerical model. Moreover, a new simplified method to estimate the capacity interaction diagram of a square TSRC section is proposed. •Twelve short square TSRC columns were tested under eccentric compression.•Full interaction behaviour between concrete and steel shape was observed due to the tube’s confinement.•A fibre model was developed to account for the inelastic behaviour of steel shape and concrete materials.•A simplified design method is proposed to estimate the capacity interaction diagram of a square TSRC section.