Seismic Performance of RC Circular Columns Strengthened with Self-compacting Concrete-Filled Steel Tubes

To investigate the seismic performance of RC circular column strengthened with self-compacting concrete (SCC) -filled steel tubes (SCFST), nine specimens of height 1200 mm, varying with a cross-section shape of steel tube (external diameter: 218 mm, cross-section dimensions: 200 mm x 200 mm) were tested under axial load and cyclic lateral load. Three parameters, including the axial compression ratio, the cross-section shape of steel tube, and the embedding rebars ratio, were considered in the tests. The failure mode, hysteresis curves, skeleton curves, ductility, stiffness degradation, and energy-dissipation capacity were analysed. Experimental results showed that the bearing capacity and stiffness of the strengthened column were 5.4 and 9.08 times than that of the unstrengthened column respectively, and the improvement ratio of ductility and energy dissipation reached 123% and 85.7% respectively. The bearing capacity and stiffness of the square SCFST strengthened column was enhanced by 28.57% and 42.11% respectively, compared with the circular SCFST strengthened column. With the designed axial compression ratio increasing, the bearing capacity, initial stiffness, and energy dissipation capacity of strengthened columns increased by 17-39%, 21-60%, and 15-40% respectively, but the ductility coefficient decreased by 8.56-32.4%. The bearing capacity and energy dissipation of the specimen with an embedding rebars ratio of 0.06% increased by 7.5% and 9.31% respectively, but the ductility decreased by 12.81%. When the embedding rebars ratio was 0.1%, the reinforcement effect can be basically negligible.