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

本报告的第一个目的是揭示圆形管状混凝土构件局部屈曲后断裂的尺度效应。第二个目标是研究CFT梁柱在波动轴向荷载和重复水平荷载作用下的断裂模式。1998年，第一个目标的实验工作完成。试件为直径为355mm和216mm的CFT构件，分别代表满尺梁柱和满尺支撑构件。试样在恒定曲率幅值下进行循环弯曲直至断裂。与以往小比尺试件的对比表明，对于直径小于355 mm的CFT构件，尺度效应可以忽略不计。因此，作者所建立的基于小尺寸试件的断裂预测方法可以应用于实尺寸CFT构件。1999年，完成了CFT柱的循环加载试验，其中轴向荷载与交替重复的水平荷载成比例变化，这是本报告的第二个目标。轴向载荷平均值为零，波动幅度为抗压强度的+/-20% ~ 40%。试验表明：波动轴向荷载作用下CFT柱的破坏模式基本为筒体局部屈曲后的断裂破坏；因此，本文提出的裂缝预测方法适用于上述情况。但是，还需要进一步的实验研究，使目前的实验对CFT试件的轴向波动情况或材料性能有一定的限制；而对于梁柱构件通常存在的小应变幅值的断裂信息缺乏。

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.