Compressive and Flexural Behavior of RC Columns Laterally Prestressed by High-strength Steel Bars

Abstract

A dry column confining method using high-strength steel bars proposed by one of the authors is applied to a total of 24 reinforced concrete (RC) columns. Two series of tests were conducted on these columns. Hoop steel ratio of the columns was 0.1%, typical of RC columns designed before the Japanese Building Code in 1981. These RC columns were laterally reinforced using 19 sets of four high-strength steel bars and L-shaped steel blocks that were attached around the column by tightening the high-strength steel bars. Five specimens were exposed to concentric compression. Uniform bending test was conducted on 9 specimens under constant axial load. High-strength steel bars were pre-tensioned before testing. The amount of pre-tension was controlled by strain in the bars. It was found that the new confining method is effective to increase ductility of the RC columns. Strength of a RC column increases in a proportional manner to the amount of pre-stress in high-strength steel bars. Strength estimation method is proposed. The measured strength varied between 93% to 116% of the calculated strength.