軸圧縮力が作用する薄肉八角形断面部材の局部座屈耐力

Cold-formed steel members are widely applied in columns and other axial members in steel structures. One of the key issues in design of cold formed steel is local buckling strength under axial compression. As a means to avoid premature local buckling, we have paid on attention to the application of octagonal section members. The local buckling behavior of octagonal section members have been investigated by many researchers. However, these studies have focused mainly on regular octagonal sections and do not considered the restraining effect between adjacent plate elements. In this paper, we conducted numerical analysis (Finite Strip Analysis and Finite Element Analysis) and stab column tests, to investigate the elastic buckling strength and post buckling strength of octagonal section members where the adjacent plate elements have different width-thickness ratios.First, we conducted Finite Strip Analysis to investigate the elastic buckling strength of octagonal section members. Through these numerical analysis, it was found that the octagonal section members generally showed higher strength than that of simply supported plate. These strength increases were depended on the difference of the width-thickness ratio between adjacent plate elements and the change of buckling mode.Second, we examined the post buckling strength of octagonal section members through a stab-column compression test. We compared the post buckling strength of square section and that of octagonal section, and found that the post buckling strengths of octagonal section members was higher than those of square section members, when they have a same diameter. In addition, it was known that the post buckling strength of octagonal section members could be evaluated by the traditional effective-width method, where simply supported conditions were assumed.Finally, we investigated the post buckling strength of each plate elements of octagonal section members whose adjacent plate elements have different widths by Finite Element Analysis. The post buckling strength of the plate elements with a large width was higher than of square section member. On the other hand, the post buckling strength of the plate elements with a small width was lower than that of square section member. These increase and decrease were dependent on the restraining effect between adjacent plate elements. Because of this trade-off effect between the adjacent plate elements, the effective width method, which regarded each plate e