How do they put cranes on the top floors when constructing high Sky Scrapers?

You see cranes on the floor which rise about 50 metres, but sometimes, when building high sky scrapers, I see cranes on the 70th floor or the 80th floor. How do they put the the crane so high up there when it can only go up high around 60-70 metres?

2 Responses to “How do they put cranes on the top floors when constructing high Sky Scrapers?”

  1. michael  on December 9th, 2012

    The cranes are built in the elevator shafts and moved up as needed during work progress.

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  2. John B  on December 9th, 2012

    these cranes are self raising. as they need to go higher they raise themselves up on hydraulic jacks and another section is bolted in the gap that is left. i hope this will answer your question

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