Structural performance of repaired circular reinforced concrete columns using steel strapping tensioning technique

Studies on the behaviour of intact reinforced concrete (RC) columns are widely available, however, studies focusing on the behaviour of deteriorated RC columns is quite limited. Deteriorated columns need to be repaired to remain structurally sound. Among the available repairing approaches, confining methods have been extensively researched. Current studies on confining damaged column only focusing on passive-typed confinement, which led to high dependency of the dilation of concrete. This study extends the investigation on repairing RC columns to the active-typed confinement, where confining stress is applied to columns before the concrete dilation. Both experimental and numerical modeling were conducted to investigate the applicability of active confinement in repairing RC columns with varied pre-damaged levels. The applicability of steel strapping confinement in repairing RC columns with the varied pre-damaged levels were confirmed through experimental works, the experimental involved testing of 34 plain concrete cylinders and 21 RC columns under monotonic uniaxial compression. The concrete cylinder tests were performed develop a suitable stress-strain model, which incorporated pre-damaged levels for confined concrete. The empirical stress-strain model was then used in the development of numerical model for the repaired RC columns. The tests on RC column specimens consisted of 3 control columns and 18 repaired RC columns with different confining levels. The overall response of the specimens was investigated in terms of crack pattern, load carrying capacity, axial displacement, stiffness and ductility of repaired columns. The results from the experimental works were then verified by using the numerical modeling before further analysis. The test results have shown that the restorability of confinement was significantly affected by pre-damaged levels. It is also observed that the increase in confining volumetric ratio is able to restore both strength and ductility of repaired RC columns up to 171% and 172%, for the same pre-damaged level. Additionally, the outcome of the finite element modelling also aligned with the experimental results where the average absolute errors (AAE) for both strength and ductility remained are within 15%. Based on this study, a design consideration for repairing columns using confinement was also developed. The design consideration serves as a tool for design engineers in using steel strapping confinement in repairing damaged columns