角形鋼管の局部座屈性状と幅厚比評価について

抄録

As evaluation methods of the width-to-thickness ratio of the square steel tube, there are two concepts : one is to use the total width, and the other is to use the width of the flat plate portion. This is due to the fact that although the constraint effect of the corners on local buckling is recognized, it has not been made clear how effective is the constraint. As the object of this study, short columns subjected to axial compression have been chosen, we have investigated the constraint effect of corners on local buckling and plastic deformation capacity, and the evaluation method of the width-to-thickness ratio of the square steel tube analytically. The results from the study are as follows. (1) Changes in deformation properties of a square steel tube when the radius of curvature of corners increases, resemble those in deformation properties of the box section steel tube when the width-to-thickness ratio is reduced, and the increase in the radius of curvature is recognized to have the same effect as a reduction of the width-to-thickness ratio. (2) Assuming that the width-to-thickness ratio of the box section steel tube, which has the same plastic deformation capacity as that of the square steel tube, is the equivalent width-to-thickness ratio, the width-to-thickness ratio evaluation of the flat plate portion is on the dangerous side, because the equivalent width-to-thickness ratio becomes greater than the width-to-thickness ratio of the flat plate portion. (3) For the ordinarily-used square steel tube (corner radius of curvature R≦3× plate thickness t), the constraint effect of the corners does not greatly increase plastic deformation capacity, and therefore, the width-to-thickness ratio evaluation method on the basis of the total width is appropriate.