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.