how do they erect those huge cranes for constuction?

Question

do they start with the crane house and keep adding sections underneath it? Or do they build they tower and then somehow top it with the actual crane?

Answer 1

How Do They Grow?
Tower cranes arrive at the construction site on 10 to 12 tractor-trailer rigs. The crew uses a mobile crane to assemble the jib and the machinery section, and places these horizontal members on a 40-foot (12-m) mast that consists of two mast sections. The mobile crane then adds the counterweights.
The mast rises from this firm foundation. The mast is a large, triangulated lattice structure, typically 10 feet (3.2 meters) square. The triangulated structure gives the mast the strength to remain upright.

To rise to its maximum height, the crane grows itself one mast section at a time! The crew uses a top climber or climbing frame that fits between the slewing unit and the top of the mast. Here's the process:

The crew hangs a weight on the jib to balance the counterweight.
The crew detaches the slewing unit from the top of the mast. Large hydraulic rams in the top climber push the slewing unit up 20 feet (6 m).
The crane operator uses the crane to lift another 20-foot mast section into the gap opened by the climbing frame. Once bolted in place, the crane is 20 feet taller!

Once the building is finished and it is time for the crane to come down, the process is reversed -- the crane disassembles its own mast and then smaller cranes disassemble the rest.

Answer 2

As described above, but the crane that is being used in our plant arrived in 80 semi truck loads!

Answer 3

The cranes are taken to the top of the buildings in pieces and then they are built together whilst up there.

Answer 4

I'm sorry, but there is no way that a crane can lift another section of itself up in the manner described by the first person ("lift another 20-foot mast section into the gap opened by the climbing frame"). Can you lift yourself off the ground by pulling up on your own collar?

I was told that the crane is jacked up from the bottom, and they slide another section below the jacked up crane. Then they lower and bolt the crane to the new section that was inserted under the bottom.

Answer 5

Sorry Randy G but Dane is perfectly correct in his answer.

Answer 6

helicoptors
Watch Discovery Channel Extreme engineering they show how many things are built and the equipment needed

Answer 7

very carefully