EXPERIMENTAL STUDY ON REINFORCED CONCRETE-FILLED STEEL SQUARE TUBULAR COLUMNS WITH TIE BARS

The tests were conducted on three reinforced concrete-filled steel square tubular columns with tie bars, which included one axial compressive test for S-1 and two pseudo-static tests for S-2 and S-3. The bearing capacity, failure modes, failure paths, hysteretic energy dissipation capacity, displacement ductility, strength and stiffness degradation were examined. The research indicated that the compression deformation occurred to specimen S-1. Binding action was provided for concrete by steel tubes. The expansion from concrete to steel tubes occured because of the concrete’s cracking inside and bulking. Half-wave shapes of the steel tubes between tie bars occurred due to the bucking of thin steel tubes and the local constraint of tie bars. The bottom of concrete was crushed and steel tubes was buckled in quasi-static tests. The bottom of specimen S-3 without reinforcing stiffening rings at the two ends and with smaller shear span-to-effective depth ratios was more seriously damaged and the energy dissipation capacity was lower than specimen S-2. A design formula to calculate axial bearing capacity of columns was proposed, and the influence of the constraint effect from tie bars on the plastic hinge length of column ends was discussed.