25 September 2010- Skyscrapers have become a permanent part of any city landscape, providing the ability to utilize a large amount of space in a small section of city real estate. These great buildings would not be possible without the advent of the crane, which allows construction crews to build upward instead of outward. There are two types of cranes that are mainly used in the construction of tall skyscrapers. One is the tower crane, which is the large crane with a single swinging arm that is seen on the outside of buildings, and the other is the self-erecting crane, which stands inside the building.
Raising the Crane
When building a skyscraper, builders must find a way to lift the cranes
so that they can assist in the assembly of the skyscraper. The way that this is accomplished with tower cranes is by using a jack to lift the crane. The jack, which surrounds the shaft of the crane, slowly lifts up a section of the crane, and then allows for more parts to be placed into the shaft and bolted into place, thus growing the crane. Another type of crane is the self-erecting crane which sits inside the building and lifts itself up using jacks, allowing it to be lifted and placed on each newly constructed floor, thereby rising with the building.
Disassembling the Cranes
Removing these massive cranes from a construction site is a difficult procedure. The largest crane, the swinging-arm tower crane, must be disassembled piece by piece and lowered. This is done by using the smaller self-erecting crane, which is now sitting on the roof of the building, to dismantle and lower the parts of the tower crane. The self-erecting crane is still, however, too large to be removed from the site without assistance, and at this point a small derrick crane will be brought to the roof. This crane is small enough to be brought up through the elevator piece by piece and assembled on the roof. Once this crane has disassembled the self-erecting crane, it is then disassembled by hand and brought back down through the elevator.
Source: Aram Khayatpour, www.ehow.com