| 摘要 |
A tower crane is carried on a platform rotatably mounted on a large ring with the tower pivotally mounted on the forward portion of the platform above the ring and a mast mounted on the platform adjacent the boom and extending upwardly and rearwardly therefrom. A counterweight support at the rear end of the platform also rides on the ring and is connected to the top of the mast by a backstay. At the top of the tower is a pivotally mounted, forwardly projecting boom and an upwardly and rearwardly inclined boom strut whose upper end is pin-connected to the top of the mast by a backstay strut. A tower backstay is connected to an upper part of the tower and extends generally horizontally rearwardly to the top of the mast where it is also pin-connected. By removing the pin-connections at the top of the mast, the tower, boom, boom strut, backstay strut and tower backstay can be pivotally raised and lowered as a unit by powered erection rigging mounted on the platform. A pendant is connected between an intermediate point on the tower backstay and a lower point on the tower to insure that the openings for the pin-connections at the top of the mast are properly aligned when the tower is erected. Additional hoist mechanisms and rigging are carried on the platform for adjusting the boom angle and for raising and lowering a load. In the preferred embodiment, the crane includes two laterally spaced towers, booms, masts, backstays and struts interconnected as described above.
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