Abstract: To improve the ductility and bearing capacity of concrete columns,this paper proposed a composite strengthening method with prestressed steel strips and external steel frames.Axial compression tests were conducted on two concrete columns and thirty-six strengthened concrete columns,which included two columns strengthened with prestressed steel strip,two columns strengthened with external steel frame,and thirty-two columns strengthened with the composite method.The influences of steel strip configuration (spacing and layers),external steel frame configuration (tensile strength,thickness,and radius),and initial axial compression ratios on failure modes,bearing capacity,ductility,and energy dissipation capacity of strengthened columns were analyzed.Test results show that the proposed composite strengthening method is an efficient method,which combines the advantages of prestressed steel strip method and external steel frame method,and can significantly improve the ductility and bearing capacity of concrete columns at the same time.The strengthening effects of the composite method on concrete columns increase with decreasing steel strip spacing and increasing steel strip layers.The increase of tensile strength and amount of external steel frame can improve the bearing capacity and energy dissipation capacity of columns,when the amount of steel strip is enough to prevent the global buckling of external steel frames.In addition,the initial axial compression ratios have limited effects on the compressive behaviours of strengthened columns.Moreover,a prediction equation was developed to calculate the compressive bearing capacity of the composite strengthened columns and the calculated results agree well with the experimental results.