Abstract: Eight reinforced concrete columns were designed and strengthened with high ductile concrete (HDC) and grouting material. The failure modes, strength enhancement mechanics and shear capacities of the specimens were studied by static cyclic loading tests. The experimental results indicate that the HDC strengthening jacket could provide a good confinement for the core concrete. The failure mode is changed from brittle failure to ductile failure. The shear capacity and deformability of the specimens are significantly improved. Theoretical analysis is carried out on the strength enhancement mechanics for columns strengthened with HDC jackets. A calculation method of the shear capacity of strengthened columns is proposed based on the truss-arch model. The calculated results have good agreement with the test results.