| More and more buildings are badly in need of strengthening for the sake of ageing.In this paper, based on the existing strengthening method and the mechanical behavior of recycled aggregate concrete filled steel tube(RACFT) columns, a reinforcement method is put forward. The RC columns are strengthened by recycled aggregate concrete(RAC) and steel jacket which can either take advantage of steel tube to improve the mechanical properties of column structure, but also can reuse the waste concrete as recycled concrete and achieve the purposere of sustainable development. In order to study the mechanical properties of the RC column strengthen by this strengthening method subjected to axial compression, the main following aspects are carried out in this paper:(1) A total of 19 specimens including one RC column without strengthening, twelve RC columns strengthen by RAC and circular steel jacket, two concrete filled steel tubular columns and four RC columns strengthen by RAC and square steel jacket were conducted under axial compression. The main parameters comprised: recycled coarse aggregate replacement ratio, thickness of steel tube, initial axial compression ratio of original column and section of steel tube. The test results showed that the bearing capacity, stiffness and ductility of the specimens are significantly improved after strengthening. For circular specimens, the bearing capacities of the specimens with RAC were a little smaller than the specimens with nature aggregate concrete(NAC). Whereas, the influence of replacement ratio on the bearing capacity and ductility of the specimens is not obvious. Larger thickness of steel jacket could behave higher bearing capacity. The initial axial compression ratio of original column showed little impact on the bearing capacity of the steel-jacket retrofitted columns. For square specimens, the bearing capacities of the ribbed specimens increased obviously compared to the un-ribbed one. Meanwhile, the increases number of the ribs could also improve the bearing capacity of the specimen accordingly.(2) Based on test result, further analysis by FEA software ABAQUS were also conducted. The results showed that the developed finite element model can simulate the stress state and bearing capacity of the circular specimens well. The parametric analysis results showed that for the bearing capacity of circular specimens, the influence of the steel yield strength and thickness of the steel tube are more significant than the RAC replacement ratio and RAC strength. The impact on the bearing capacity of the original column initial axial compression ratio is little.(3) Different formulas were used to calculate the bearing capacity of the specimens in this paper. The comparison between the test and calculation showed that, these formula were more accurate in the calculation of bearing capacity of circular specimens than the square specimens. Among the formulas, the results of EC4 code give the highest precision and the smallest discreteness, which is suggested for designing. On the other hand, the calculation results of the square specimens were higher than the test ones. |
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