Behavior of Strengthened and Repaired Reinforced Concrete Columns under Cyclic Deformations

The behavior of strengthened and/or repaired reinforced concrete short columns under cyclic deformation was studied. The primary objective of the study was the evaluate the effectiveness of various techniques for strengthening or repairing short columns. Based on an 18-in. square prototype column, three column test specimens were constructed to two-thirds scale, using identical geometry and reinforcement. The original specimens had a 12-in. square cross section reinforced with eight #6 longitudinal bars, sets of 6 mm ties spaced at 8 in., and 1 in. cover. Spacing of the transverse reinforcement, though greater than what would currently be specified, was intended to represent the practice of column design in seismic regions of the U.S. in the 1950's and 1960's. One of the original specimens was tested. The remaining two specimens were strengthened prior to testing. A single lateral displacement history was used for all tests. Constant axial load was applied. Both the strengthened and the repaired columns exhibited greater ductility than the original column. Jacketing both with and without supplementary crossties resulted in much greater stiffness and strength than that of the original, unstrengthened specimen. The repaired specimen had much greater lateral stiffness and strength than the original specimen, but did perform as well as the strengthened specimens.