| 摘要 |
PROBLEM TO BE SOLVED: To improve workability upon manufacturing by securing needed strength and rigidity by using a welding bead without specially adding a plate material, increasing a thickness of a plate or the like. SOLUTION: A boom 11 having a closed quadrangular cross-section structure is made by joining right and left webs 12, 13 and upper and lower flanges 14, 15 to one another. Rib-like projections 21, 21 extending to have a zigzag form are formed on outer surfaces of central web plates 12C, 13C of the right and left webs 12, 13 in a longitudinal direction of the central web plates 12C, 13C by cumulating the welding bead. Thus, the rib-like projection 21 formed by the welding bead is utilized as a reinforcing rib of the central web plates 12C, 13C, being the flat plate materials, to enhance the strength of the central web plates 12C, 13C, and to improve bending strength, twisting strength, or the like of the boom 11 as a whole. COPYRIGHT: (C)2007,JPO&INPIT
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