Big cranes!

[siclark]

How the hell do they put up those big building cranes? I mean surely they need a crane just as big to get the bits up...? Maybe...? Arrgghh!

[cupra]

They build the jib first, then jack it up and insert the supporting sections!

[rinkytink]

When they get to a certain height the real big cranes can 'build themselves'. Not too sure of the technical details but they have the ability to add sections onto themselves.

[sddsddean]

I assume you mean tower cranes (lattice work giant T's) rather than normal mobile cranes (with about 8 axles). There are 3 basic ways. If the crane is fairly short (say <15m), they can come folded up. You take off the set of road wheels, and it 'unfolds' itself. For cranes up to about 30m, it is usually more economic to erect it using a normal mobile crane to lift the sections into place. For anything bigger (I think the record at the moment is held on a site in Germany at about 400m) the crane is self erecting. At this sort of height the crane is usually braced either to the side of the structure, or often goes up a lift shaft. In these cases, rather than build the whole thing at once, it grows with the building. It has a section (usually under the cab) which can extend 3m on hydraulics. The crane then lifts the next tower section up and its slotted into place and bolted home.

[cupra]

I discovered an interesting fact looking into this; a tower crane in Las Vegas (erecting a skyscraper) was so large, the had to erect another smaller crane on top of the skyscaper to dismantle it, and then another even smaller crane to dismantle this one!

[Lal]

hydraulically