Generally the base which is bolted into a large concrete pad provides the necessary support for a tower crane. The base is attached to a mast or a tower and stabilizes the crane which is affixed to the inside of the building's structure. Normally, this attachment point is to an elevator shaft or to a concrete lift.
Usually, the mast is a triangulated lattice structure measuring 0.9m2 or 10 feet square. The slewing unit is attached to the very top of the mast. The slewing unit consists of a gear and a motor which allows the crane to rotate.
Tower cranes are able to have a maximum unsupported height of 80m or 265 feet. The tower crane's maximum lifting capacity is 16,642 kg or 39,690 pounds with counter weights of 20 tons. In addition, two limit switches are used in order to ensure the operator does not overload the crane. There is even one more safety feature known as a load moment switch to ensure that the operator does not surpass the ton meter load rating. Lastly, the maximum reach of a tower crane is 70 meters or 230 feet.
Due to their extreme heights, there is a science involved to erecting a crane. The stationary structure will first need to be brought to the construction location by using a huge tractor-trailer rig setup. Next, a mobile crane is utilized in order to assemble the equipment part of the crane and the jib. These parts are then connected to the mast. Next, the mobile crane adds counterweights. Crawler cranes and forklifts could be a few of the other industrial machinery which is utilized to erect a crane.
Mast extensions are added to the crane when the building is erected. This is how the height of the crane is able to match the building's height. The crane crew uses what is called a climbing frame or a top climber which fits between the slewing unit and the top of the mast. A weight is hung on the jib by the work crew so as to balance the counterweight. Once complete, the slewing unit is able to detach from the top of the mast. In the top climber, hydraulic rams are utilized to adjust the slewing unit up an additional 6.1m or 20 feet. After that, the operator of the crane utilizes the crane to insert and bolt into place another mast part piece.