| 摘要 |
A torsion- and bending resistant boom formed of beams running the length of the structure, a set of pierced, transverse flanges arrayed along, and substantially perpendicular to, the length of the structure, a continuous longitudinal member running the length of the structure, piercing the flanges, and several further longitudinal members, outward of the first member. The longitudinal members are welded to the flanges. An elevatable mast assembly raises and lowers the boom, and has a mast and guides formed of hollow tubes, and rollers between the guides and the mast, the rollers transferring torque loading to the guides.
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