Strengthening damaged columns on the soft first story of reinforced concrete building using ultra-high-strength fiber-reinforced concrete panels

In this study, ultra-high-strength fiber-reinforced concrete (UFC) panels were used as a quick and effective measure for seismic strengthening of damaged reinforced concrete (RC) columns. Four 1/3-scale specimens, which replicated RC columns of the soft-first_story of a 10-story condominium building that was heavily damaged in the 2016 Kumamoto Earthquake, were constructed and tested. The specimens were strengthened using UFC panels after being preloaded to the drift ratio, at which the maximum load capacity of the target column was measured, and then subjected to the main loading until the ultimate state was reached. The UFC panels were installed on the two faces of the column in a direction parallel to the assumed loading direction. Two of the specimens had a UFC or RC wing wall attached to one side of the column, which was also aligned with the assumed loading direction. During the preloading and main loading, the specimens were subjected to a cyclic lateral load and varying axial load that simulated an earthquake load. The proposed method improved the maximum strength and ultimate drift ratio, and helped restore the initial stiffness of specimens with UFC panels and a wing wall to that of a column specimen during preloading. The test results of a previous study, wherein the target column, loading method, and strengthening method were the same but the specimens were not damaged before strengthening, were compared to study the impact of the damage on the RC column before strengthening.