Restoring Force Characteristics of CFT-Column under Seismic Load

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1) Experimental Study on Ultimate Behaviors of High-Strength Concrete Filled Steel TubeTo investigate the ultimate behavior of high-strength concrete filled steel tube (CFT), dynamic loading test of CFT column has been carried out. From the test results it is shown that the steel tube of CFT column cracks in the ultimate state and the fracture of CFT column is brittle.2) Ultimate Bending Strength of High-Strength Concrete Filled Steel tube ColumnOn the basis of stub-column test of concrete filled steel tube and calculation of steel tube stress, the equation of confined concrete strength of CFT column is derived. By the use of the equation of confined concrete strength, the method to predict the ultimate bending strength of CFT column is proposed. This method can predict well the maximum bending strength of CFT column test even if CFT column is the super high-strength concrete filled steel tube.3) Crack of Steel Tube and Plastic Deformation Capacity of Concrete Filled Steel Tube ColumnThe ultimate state of CFT column due to the steel tube crack is examined and the condition of fracture is obtained on the basis of test data. By the use of this fracture condition the equation to calculate the accumulated plastic deformation capacity of CFT column is proposed.4) Restoring Force Characteristics and Model of Concrete Filled Steel Tube ColumnA restoring force model of CFT column is obtained from the cyclic loading test of CFT column. The proposed restoring force model is composed of the Tri-linear model and the Clough model and easily applicable to seismic response analysis of CFT frames under strong ground motion. The proposed model is defined by the yield strength, the ultimate strength and the accumulated plastic deformation capacity of CFT column. By the use of the energy absorbing capacity of CFT column, it is ascertained that the presented model can predict well the restoring force characteristics of the CFT specimens.