Experimental Research On Seismic Behavior Of RC Column Strengthened With Recycled Concrete Filled Steel Jacket

Both the strengthening of old buildings and recycle of waste concrete have become significant issues in building industry. To achieve sustainable development, an innovative concept of steel-jacket retrofitted columns(SJRC) with recycled aggregate concrete(RAC).was put forward in this thesis, in which the common RC column is encased by a steel jacket, and the gap between the tube and the original column is filled with RAC for integration purpose. As this type of strengthening column using new material and new technique, its seismic behavior needs to be demonstrated by test and analysis. Tests on ten specimens were carried out in this thesis to investigate the seismic behavior of SJRC. The work has been done as follows:(1) The cyclic loading tests on an RC column and nine strengthening SJRC were carried out to investigate the influence factors as follows: axial compression ratio, thickness of the steel jacket, replacement ratio of recycled coarse aggregate(RCA), pre-damaged and preload on original column. It turns out that the SJRC has a great improvement in seismic behavior than the RC column. The bearing capacities of SJRCs are 1.6~2.6 times of the RC column, and the ductility of SJRCs are more than twice of that of the original one. As the axial compression ratio varies from 0.20 to 0.66, the bearing capacity of SJRCs increase. As the thickness of the steel jacket increases, the bearing capacity, ductility, and energy consuming capacity improve with the axial compression ratio of 0.66. Moreover, the replacement ratio of RCA has little influence on stiffness, bearing capacity, ductility, and energy consuming capacity, which means the appropriate use of RAC can also behave good seismic performance. The bearing capacity of pre-damaged column strengthened by SJRC is 6.8% lower than that of undamaged one. The preload on original columns in this thesis has positive effect on bearing capacity, but negative effect on ductility.(2) The results of ABAQUS analysis shows that FEM simulates well in skeleton curves, hysteretic curves, and strain evolution and distribution of test results. Detailed FEM analysis about stress revolution in the whole loading process indicated that the failure mode can be defined as tensioncontrolled failure and compression-controlled failure. The tension-controlled failure shows better ductility due to the yielding of the longitudinal bar, while the compression-controlled failure is brittle because of the crushing of the concrete.(3) Parametric analysis by FEM was carried out, aiming at the following influence factors of SJRCs: axial compression ratio, thickness of the steel jacket, replacement ratio of RCA, axial compression ratio of original column, and boundary condition of column bottom. The results show that the bearing capacity of SJRC increases with the raise of axial compression ratio when the SJRC failed by tension-controlled, but decreases when the SJRC failed by compression-controlled. The increase of thickness of the steel jacket can improve the bearing capacity and stiffness. The raise of the replacement ratio of RCA has negative effect on bearing capacity, but the effect is limited with a reduction up to 4.2%. The preload on the original column has positive influence on bearing capacity when the SJRC failed by tension-controlled, but negative influence when the SJRC failed by compression-controlled. In general, the bearing capacity of SJRC is lower than that of the concretefilled steel tube(CFST) column except the case when the the steel tube is thin enough.(4) The working mechanism of SJRC under compression-bending condition is put forward and summarized in this thesis, and calculation on its bearing capacity is carried out. It shows that the assumption and analysis about this mechanism corresponds to the test results.