COLUMNS SUBJECTED TO AXIAL FORCE AND

BENDING MOMENT

Hysteresis characteristics of concrete filled steel tubular columns have been proposed.
However, it has not been clarified if the skeleton curve could be applied for slender
columns, and there are few studies about the unloading stiffness of the hysteresis loop.
The purpose of this study is to compare the skeleton curves of square CFT columns,
which have been proposed by the moment-rotation angle relationships and the
experimental data by the previous research. The relationship between the initial
stiffness obtained by the theoretical calculation and the unloading stiffness obtained by
the experimental study are shown. Also the effects of the axial force ratio and the
width-thickness ratio on the above mentioned relationships are discussed. The loading
condition of the experimental study is monotonic and cyclic loading. It is found that
the skeleton curve evaluates conservatively the bending moment-rotation angle
relationships obtained by the test in both loading conditions, except for the width-thickness
ratio 43 specimen with cyclic loading. The ratio of unloading stiffness _{ex}K_{r}
obtained from the experimental data and calculated theoretical stiffness K was shown.
The effect of the axial force ratio on the _{ex}K_{r}/K was observed when the rotation chord angle was more than 1% and the width-thickness ratio increased as _{ex}K_{r}/K decreased.