How do they do this?

Question

I have always wanted to know the answer to this question, perhaps some of you engineers or builders out there can answer it. When building a very large or tall building, cranes are often perched on top. How do they get the crane up there and how do they move it to the top of each level as it gets higher. More importantly, how do they get the crane down once the building has finished? It can't be from another crane as none would be that tall....

Answer 1

The crane is assembled on the ground before the building is built by a mobile crane from trucked in pieces. The crane itself can lift itself up section by section as the building rises using a special apparatus built into the base of the crane itself. Once the building is done, the crane is designed to lower itself to the ground piece by piece.

Answer 2

Looks like the shorter ones are removed with a mobile crane (first link), and the description at the second link describes disassembly of the crane and lowering the pieces with a block and tackle (think "winch").  Not sure exactly how this is done, but given that a winch can handle more than its own weight a large winch could be lowered with a smaller one and so forth until the remaining equipment can come down one of the building elevators.

Answer 3

The crane breaks down in to small pieces.