Mechanical behavior of square RC columns strengthened with concrete filled steel tube under eccentric load

Eight RC columns strengthened with concrete filled steel tube and one unstrengthened RC column were tested under eccentric load. The results show that the strengthening method significantly improves the ultimate bearing capacity and the ductility of the original RC columns. With the wall thickness of steel tube increasing, the strengthened columns show an increasing trend in the bearing capacity and the ductility. With the compressive strength of strengthening concrete increasing, the strengthened columns show a slightly increasing trend in the bearing capacity but a significantly decreasing trend in ductility. Based on the experimental results, the mechanical properties of the strengthened columns under eccentric load were analyzed by ANSYS. Comparative results with the experimental results indicate that the numerical model is effective, and the maximum error of calculated strengths is 6%. The analysis results of the finite element method show that the inside strengthened concrete is obviously confined by the steel tube and the maximum confining stress is up to 10 MPa, while the outside strengthened concrete is under tension and is not confined. Moreover, the confining stress of original concrete is roughly similar everywhere and is between 2.0 MPa and 2.5 MPa. Because of the effective confinement provided by the circular steel tube, the maximum stresses of original concrete and strengthening concrete are more than their uniaxial compressive strength. © 2016, Editorial Office of Journal of Building Structures. All right reserved.