Behaviour and strength of steel jacketed RC columns under concentric axial load

Abstract

Reinforced concrete (RC) columns often need strengthening to improve their load carrying capacity and ductility to sustain the applied loads. This research investigates the behavior and strength of the RC columns strengthened with steel jacketing method. An experimental investigation was carried out on deficient RC columns with steel angles and strip jacketed under concentric axial loads. The experimental program consists of eight square deficient RC columns with similar longitudinal steel ratio and low concrete strength. Mimic to the practical situation, they were made deficient further by preloading up to 70% of their ultimate load. The failure behavior, post-peak responses, and ultimate loads were observed during testing. The effects of the parameters: steel angle ratio, spacing of the horizontal strips, preloading state and partial strengthening method applied at column ends were investigated from the experimental results. Finally, the experimentally obtained capacities for the preloaded strengthened columns were compared with theoretical capacities calculated using available analytical models. The performance of the particular steel jacketing method was found to be very efficient. Significant improvement in ultimate load and ductility was obtained in the study. The failure in most of the strengthened specimens was due to the buckling of the steel angle followed by crushing of the concrete. From the test results, it has been found that the strengthened columns improve their load carrying capacity (ranging from 87% to 186%) and ductility (ranging from 31% to 67%) than the unstrengthen RC columns. This enhancement in ultimate capacity was observed to be reduced by 27% due to the application of 70% preloading to the RC columns before strengthening. The increase in steel angle ratio from 4% to 7% provided highest contribution in improving the ultimate strength of the preloaded column with respect to the unstrengthen column. On the other hand, decreasing the strip spacing from 300 (2d) to 150 (d) mm resulted in an increase in the capacity of the preloaded columns by an average value of 15% only. However, the ductility of the columns were improved significantly by about 60% due to the reduction in strip spacing. The available capacity prediction models for unloaded strengthened RC columns can be safely applied for preloaded strengthened RC columns.