Flexural Behavior of Reinforced Concrete Columns Strengthened with Wire Rope and T-Plate Units

Abstract

Unbonded techniques to strengthen reinforced concrete columns have become increasingly popular. This study evaluates the flexural behavior of reinforced concrete columns strengthened with unbonded wire rope and T-shaped steel plate units. Seven strengthened columns and an unstrengthened column were tested to failure under constant axial load and cyclic lateral loads to explore the significance and limitations of the strengthening procedure developed for resistance against earthquakes. The main variables investigated were the volume ratio of wire rope, axial load level, and the presence of mortar cover for strengthening steel elements. In addition, the theoretical monotonic lateral load-displacement curve for strengthened columns is simply derived using the combination of section laminae method and the idealized curvature-displacement relationship. The findings show that wire rope and T-shaped steel plate units were highly effective in preventing spalling of concrete cover and buckling of longitudinal reinforcement. The flexural capacity of columns strengthened without mortar cover was slightly higher than that of the unstrengthened column, but the flexural capacity of strengthened columns with a 60 mm (2.36 in.) thick mortar cover was at least 2.5 times higher than that of the comparable strengthened columns without mortar cover. The developed strengthening procedure was particularly effective in enhancing the ductility of the columns, showing that the displacement ductility ratios and work damage indicators in the strengthened columns were much higher than in the unstrengthened column. The monotonic lateral load-displacement relationship of the column specimens predicted from the proposed numerical analysis is in good agreement with backbone curves obtained from measured cyclic lateral load-displacement relationships.