Kenji Sakino

Hysteretic Behavior of Concrete-Filled Steel Tubular Columns under Uniform Bending

In order to evaluate the load carrying capacity and ductility of hinging zone of the concrete filled steel tubular (CFT) columns, tests are carried out on 12 circular specimens and 18 square specimens subjected to uniform bending under a constant axial load. The experimental parameters are: 1) depth to thickness ratio (D/t ratio) and width to thickness ratio (B/t ratio) of steel tube; 2) axial load ratio; 3) material strength; 4) deformation history; and 5) annealing. One of the features of the test is the wide range of D/t and B/t ratio. The range of D/t ratio of the circular CFT columns is 40.5-160 and the range of B/t ratio of the square CFT columns is 32.8-98.0, respectively. The experimental load-deformation relations are compared with those of the elasto-plastic analysis based on the supposed stress-strain relationships established for the filled concrete and for the steel tube. The analytical results show good agreement with the test results for all specimens. This implies that the proposed stress-strain relationships for CFT columns are useful to predict the characteristics of the filled concrete and the steel tube.

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

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.