Usually the base that is bolted into a big concrete pad provides the essential support for a tower crane. The base is connected to a mast or a tower and stabilizes the crane which is attached to the inside of the building's structure. Often, this attachment point is to an elevator shaft or to a concrete lift.
The mast of the crane is often a triangulated lattice structure which measures 0.9m2 or 10 feet square. Connected to the very top of the mast is the slewing unit. The slewing unit is made of a gear and a motor that enable the crane to rotate.
Tower cranes are able to have a maximum unsupported height of 80m or 265 feet. The maximum lifting capacity of a tower crane is 16,642 kg or 39,690 lbs. with counter weights of 20 tons. Additionally, two limit switches are used in order to ensure the operator does not overload the crane. There is even one more safety feature referred to as a load moment switch to ensure that the driver does not surpass the ton meter load rating. Finally, the tower crane has a maximum reach of 230 feet or 70 meters.
Due to their extreme heights, there is a science involved to erecting a crane. The stationary structure will at first need to be brought to the construction site by using a huge tractor-trailer rig setup. Next, a mobile crane is utilized so as to assemble the equipment part of the crane and the jib. These sections are then attached to the mast. Afterward, the mobile crane adds counterweights. Crawler cranes and forklifts could be some of the other industrial machinery which is usually utilized to erect a crane.
Mast extensions are added to the crane as the building is erected. This is how the height of the crane could match the building's height. The crane crew utilizes what is called a top climber or a climbing frame 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 could detach from the top of the mast. In the top climber, hydraulic rams are used to adjust the slewing unit up an extra 6.1m or 20 feet. Then, the crane driver utilizes the crane to insert and bolt into position one more mast part piece.