A STUDY ON THE POST-LOCAL-BUCKLING FRACTURE OF CONCRETE FILLED CIRCULAR TUBES UNDER CYCLICLOADING

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The first objective of this report is to reveal the scale effect on the fracture following local bucking of concrete-filled circular tubular members (CFT members). The second objective is to investigate the fracture mode of CFT beam-columns subjected to the fluctuating axial loads as well as the repeated horizontal loads. In 1998, An experimental work for the first objective was completed. The specimens were CFT members with the diameter of 355mm or 216mm, either of which represented the full scale beam-column or the full scale bracing member, respectively. The specimen was subjected to the cyclic bending under a constant amplitude of the curvature until the fracture. The comparison with the previous small scale specimens suggested that the scale effect would be negligible for CFT members at least within 355 mm in diameter. Accordingly, the fracture prediction method which had been developed by the authors from the small scale specimens may apply to the full scale CFT members. In 1999, a cyclic loading test for CFT columns in which the axial loads varied in proportion to the alternatively repeated horizontal loads was completed as the second objective of this report. The axial loads had a zero average and fluctuated with the amplitude of +/-20% to 40% of the compressive strength. The experiment demonstrated that the collapse mode of CFT columns subjected to fluctuating axial loads was basically the breaking fracture following local buckling of tubes; and , therefore, the authors fracture prediction method was applicable to those. However, the further experimental study should be required, so that the present experiment has a limit to the condition of axial fluctuation or the material properties of CFT specimens; and the information is deficient for the fracture in the small strain amplitudes which is ordinary for beam-column members.