Could someone tell me how construction cranes are constructed? I’ve never actually seen one go up, and barring helicopter support [or a second crane], I’m baffled. It seems to me that prefabricated sections would be the only time-efficient way to do it, but how to haul all that up there without a crane has me stumped. Or are they built strut by strut, the way scaffolding is?
The crane tower is built seperately. (It also disconnects for easy transportation.) When the crane arrives at the site, the tower is connected to the cab, cables attached, and the whole thing is hauled up.
Hauled up by what? Do they use horizontal force and a big pulley? If so, what the heck is sturdy enough to attach that pulley to?
I think MRknowitall is saying that is is constructed with the arm in the down position. Once it is attached, you just turn on the crane and raise it.
There is quite a lot of building going on around here so I’ve had the chance to observe. I can say that often (and I knot little else about’em) I have watched smaller cranes being used to assemble larger cranes. A REALLY BIG one near my office will be disassembled soon; I’ll try to watch and report back.
According to a friend of mine who drives trax machines, diggers etc.
First off they build a large concrete base, then the crane is assembled from sections on the ground and then hauled in one piece onto the concrete base. It’s put together on the ground with the arm in the correct position, they don’t haul it into place after raising it. The hauling is done by the telescopic arm cranes.
He says this is normally done at night which is why the cranes always just seem to spring up. At least they do around here…
One final word from him (which would be a miracle) is that it’s a VERY dangerous operation.
I have to admit my earlier explanation is a bit of a guess. I’ve seen cranes hauled around on tractor/trailers, and the crane’s arm was disconected from the cab. I pretty much guessed the rest. If someone out there knows from a reliable source, I’d love to hear it.
Thanks, everybody. A friend of mine at work came back with a similar answer and the correction that they are called “derricks;” though I am not sure if he was referring to the entire structure or the arm.
To quote myself
& Bobinelli
Sure enough, that crane was gone this morning.
Trying to make a jump correlation from oil & gas drilling, I’d guess “derrick” means the whole damn thing, but it might refer to just the supporting structure. We need definitive word from someone in that industry.
I think there’s some confusion as to what kind of crane we’re talking about…the kind that has 18 wheels and drives down the highway, or the kind that looks like a big truss arm with a counterweight sitting on top of a very tall tower. As for the mobile ones, I’m not sure how they put that last section on the crane. I’d say maybe they could lower the whole boom to the ground and somehow attach it there, but that’s just a guess. Now, if I remember this right (I think I remember David MacCaulay writing about this, but its still a bit fuzzy) The tower crane build themselves (after they’re partially assembled, that is). The section just under the boom can “crawl” up the tower section. As was previously stated, a base is built for the crane to sit on, and a tower is started on it. Once there is a section or two of tower, the crawling section is attached. The top half or so of this crawling section has a space on the side of it where another section can be slid into it, then bolted to the already in place tower. The crawling section (with boom attached above) then crawls up to the top of the newly attached highest tower section, another tower section is added through the side of the crawling section, and the crawling section then climbs up again. This process continues until the tower is the desired height. The sections are lifted to the tower by the boom that sits on top of it. To take the tower down, the reverse process is used (the top-most tower section is removed, the crawler slides down, and another section is removed). Its a bit tough to explain without drawing it out, and I’m too tired to do that right now. Maybe in the morning 
Jeremy…
I can think of no more stirring symbol of man’s humanity to man than a fire engine - Kurt Vonnegut
You see in the spring the male crane does a display dance and the fe…HUH? What?.. oh nevermind. The official bird of D allas is the building crane, in honor of which, every one is invited to the annual Wrecking Ball.
Seriously KCB is right. I had the oportunity to watch one grow once.