Behavior of short circular tubed-reinforced-concrete columns subjected to eccentric compression

The tubed-reinforced-concrete (TRC) column is a kind of confined reinforced-concrete (RC) columns using the outer encasing thin-walled steel tube which discontinues at the beam-column joints and thus does not carry any direct axial load. Although this composite column has been used in some practical applications in China, there is still a lack of sufficient experimental data and design methods for the TRC columns subjected to eccentric compression. In this paper, 18 short circular TRC columns are tested under axial and eccentric compression considering parameters of eccentricity and diameter-to-thickness ratio of the steel tube. Failure mode, axial load-carrying capacity, and stress in the steel tube of the specimens are discussed in detail. The test results indicate that the average confining stress in the columns with small eccentricity is close to that in the columns under axial load at the peak load. To validate the employed stress-strain relationship for the confined concrete, a fiber-based model is developed and the predicted results agree well with the test results. Based on the strain energy equivalence principle, a regression formula to estimate the ultimate compressive strain of concrete confined by the steel tube is proposed. The equivalent concrete stress block parameters of circular TRC members are theoretically studied and the modified values are purposely suggested for the calculation of capacity interaction diagram.