The third method is to have a heavy-lift helicopter (or ?skycrane?) airlift the crane to the top of the construction site. This must be done piece by piece?just a single segment of a crane?s tower can weigh between 3,000 and 20,000 pounds. However, because of the cost, and because flying a load-bearing helicopter over a populated area is logistically very difficult, this method is the most rare, used only a few times a year nationwide.
Bonus Explainer: How do cranes get back down? Often by constructing the very gallows that will destroy them. To disassemble themselves, tower cranes construct derricks. (Derricks are tower cranes? simpler great-granddaddy.) These derricks then help dismantle the tower cranes, and?in the case of internal climbers?lower their parts one by one to the ground using extremely long cables. (External climbers, however, can jack themselves all the way back down.) Once the parts reach the ground, they?re taken back to the rental service on flatbed trucks, then the workers take apart the derricks. Most of the derricks? parts can just take the construction elevator.
Got a question about today?s news??Ask the Explainer.
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