How does a tower crane build itself?

Tower Cranes are usually assembled up to a certain height by means of mobile cranes. Since the reach of a mobile crane is limited, a Tower Crane is equipped to build itself by adding columns to its Mast Section. In order to achieve this, a climbing frame is bolted around the top section of the mast. The slewing unit and all components above are then unbolted from the mast and fixed to the climbing frame, which elevates those using large hydraulic rams.

The gap now opened is used to fit another column, which has been pulled into position by means of the crane itself. When the crane is to be disassembled, the process is reversed.

Cranes that are built adjacent to construction sites use the concrete base as support. They also need additional columns to raise themselves. However, some cranes are built in elevator shafts and utilize the building as the support itself. In such cases, they can unbolt the lower sections and use them to build themselves as the construction progresses.