Behavior and design of slender circular tubed-reinforced-concrete columns subjected to eccentric compression

• Sixteen slender circular TRC columns are tested under eccentric compression.
• A FE model is developed and the predicted results agree well with the test results.
• A formula to estimate the moment magnification factor (η) of slender circular TRC columns is proposed.
• Design equations are established to consider the second order effects on eccentrically loaded slender circular TRC columns.

The tubed-reinforced-concrete (TRC) column is a relatively new kind of confined reinforced-concrete (RC) columns, where the outer encasing thin-walled steel tube is discontinued at the beam–column joint and thus the axial load is transferred to the RC core only. In this paper, the behavior of slender circular TRC columns under eccentric compression loads was studied. A total of sixteen specimens considering the following primary system parameters were tested: two slenderness ratios (24, 40), two load eccentricities (25 mm, 50 mm), two diameter-to-thickness ratios of the steel tube (133, 160), and two continuity conditions for the steel tube (continuous, discontinuous at mid-height). The test results indicate that the slender circular TRC specimens exhibit fairly ductile behavior and the discontinuity of the steel tube at mid-height has a small effect (≈5% on average) on the bearing capacity. A finite element (FE) model was developed to simulate the behavior of circular TRC columns under eccentric compression loads. The predicted load versus mid-span lateral displacement curves are generally in good agreements with the measured ones. To identify the influence of the key parameters on the second order effects of circular TRC columns, an extensive parametric study was carried out using the FE model. Lastly, a regression formula is suggested to estimate the moment magnification factor and simplified design equations for slender circular TRC columns under eccentric compression loads are proposed based on the section capacity analysis.