| 摘要 |
PROBLEM TO BE SOLVED: To provide a telescopic boom capable of obtaining sufficient buckling strength of a lower plate, which has been difficult to further improve the buckling strength of the lower plate in such a structure that the buckling strength is improved by three small sections.SOLUTION: In a telescopic boom having a boom in which a lower plate 11 having a cross-sectional shape of a substantially U shape and an upper plate 12 form a closed cross section, a plurality of projections 14, 15a to 15c and 16a to 16c which have cross-sectional shapes of circular arc shapes and project outward the are continuously formed on the lower plate 11. |
