| 摘要 |
On a tower crane with a three-piece jib, consisting of a jib foot linked to the tower head, a jib centre piece (8) linked to the jib foot and a jib tip (9) linked to the jib centre piece (8), a lever system (22) is provided between centre piece (8) and jib tip (9), which lever system (22) not only enables the two jib sections to be pivoted into an extended position and to be folded but in particular enables the two jib sections to be held in a statically stable extended position during operation, without additional locking elements. This lever system (22) consists of a lever (27) linked to the centre piece (8) and of a lever (28) adjacently linked to the jib tip. The levers (27, 28) are connected to one another via a common joint (29). A stay rope (30) producing a rope force (S) acts on this joint. Since the effective lever arm (a) of the rope force is large in comparison with the effective lever arm of the tensile force (Z) acting from the jib tip, the requisite rope force (S) is small. <IMAGE>
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