eli5: You know those cranes that people use to build skyscrapers? Well, how do they get the cranes up there, and how do they get them back down when construction is finished?

Question

eli5: You know those cranes that people use to build skyscrapers? Well, how do they get the cranes up there, and how do they get them back down when construction is finished?

In: Engineering

Answer 1

Going up, they can jack themselves up and insert new tower sections under the crane as the building goes up.

Going down, it helps to have a temporary second crane.

See https://www.youtube.com/results?search_query=crane+disassembly

Answer 2

They are actually built in segments and there is a self-lifting segment right below the cab that allows for the new pieces to be inserted.