| 摘要 |
PROBLEM TO BE SOLVED: To solve the problem that a nest structure cannot be applied for extension sections of a lattice jib or a lattice tower in a conventional boom structure of a crane, which has only the lattice jib or the lattice tower. SOLUTION: The extension sections 14b to 14h are formed into a hollow truncated pyramid shape. A bottom part on a contracted side of the small extension section adjacent to the large extension section is inserted into an opening part on an expanded side of the large extension section mutually for the extension sections 14b to 14d on a bottom boom side, and mutually for the extension sections 14e to 14h on a top end side to form the nest structure. Therefore, the storage status becomes compact, and the extension sections 14b to 14h have diagonals 16 on a bottom surface on the contracted side in the truncated pyramid shape, thus preventing torsion of the extension sections 14b to 14h. COPYRIGHT: (C)2004,JPO
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