Experimental Study on the Effect of Steel-Tube Replacement Ratio on the Eccentric Compression Bearing Capacity of Composite Column

The improvement effect of the external concrete to stability of the core steel-tube was demonstrated by the steel-tube replacement ratio through experimental study. The test results show that, with the steel-tube replacement ratio increasing, the ultimate bearing capacity of composite columns increased correspondingly, and the ductility of composite columns was improved obviously also. Therefore, the steel-tube replacement ratio should be involved in the formula for calculating the ultimate bearing capacity of composite columns. By finite element method and regression analysis, the slenderness ratio is amended by the steel-tube replacement ratio and the calculation results of the eccentric compression bearing capacity agreed well with the test results．