| 摘要 |
PROBLEM TO BE SOLVED: To enable local overstress applied to the middles of bottom wall fixed parts of reinforcing members to be distributed around the bottom wall fixed parts.SOLUTION: A boom 3 is cylindrically formed with right and left side walls 3A, a top wall 3B and a bottom wall 3C, reinforcing members 8 fixed to the side walls 3A and the bottom wall 3C are provided inside the boom 3, and bottom wall fixed parts 8a of the reinforcing members 8 are arranged overlapping the longitudinal ends of a lower connector 4 fixed to the bottom wall 3C. In the middles of overlapping portions of the bottom wall fixed parts 8a of the reinforcing members 8, relief parts 9 are formed which are opposed to an end part edge of the lower connector 4 and isolated from the bottom wall 3C. |
