Cyclic behavior of steel tube-reinforced high-strength concrete composite columns with high-strength steel bars

To study the cyclic behavior of steel tube-reinforced, high-strength concrete columns with high-strength steel bars, a cyclic loading test of six full-sized square columns was carried out, including one traditional reinforced concrete (RC) column and five steel tube-reinforced concrete (STRC) composite columns. The cross-sectional shape of the inner steel tube, the strength matching of the outer concrete and the core concrete, and the presence of steel fiber in outer concrete were the major parameters of the test. The research shows that steel fiber-reinforced high-strength STRC composite columns had better seismic behavior compared to RC columns. The strength matching method, where the C90 core concrete was combined with the C70 outer concrete, resulted in a better composite effect in comparison to the method of using C80 concrete in both core concrete and outer concrete. Moreover, the addition of steel fibers in outer concrete effectively reduced the damage degree and improved the ductility, resilient capacity, and energy dissipation capacity of the specimens. Finally, based on the test research and theoretical analysis, a calculation model for predicting the maximum load-carrying capacity was proposed. The model was then verified by comparing its predictions with test results.