Behavior of slender square hollow steel-reinforced concrete columns under eccentric compression

Hollow steel-reinforced concrete columns have a number of advantages such as light weight and convenient construction. In this paper, the behavior of slender square hollow steel-reinforced concrete (HSRC) columns under eccentric compression was studied. To this end, a total of eight columns were first tested to examine the influences of the shape of the cross section and the height-to-width ratio of the specimens. According to the test results, the slender HSRC columns exhibited a moderate ductility and stiffness behavior and achieved a bearing capacity higher than the superposed value of the reference hollow reinforced concrete (RC) and steel tube specimens. Then, a finite element model (FEM) was developed to simulate the behavior of the slender HSRC columns under eccentric compression. The reliability of the FEM was verified using the measured data in terms of the variation of the load with the mid-height lateral deflection, the representative mechanical performance indices, and the failure modes. The mechanisms of the different failure modes, the loading distributions of the outer RC and the inner steel tube, and the contact stress on the interface between the inner steel tube and the outer RC were also analyzed. Next, a systematic parametric analysis was conducted to study the impacts of the height-to-width ratio of the column, the hollow ratio, the steel ratio, the yield strength of the steel tube, and the strength of the outer concrete; the key influencing factors were also determined. Finally, a simplified design method was developed to calculate the sectional capacity of the slender HSRC columns under eccentric compression.