Generally the base which is bolted into a large concrete pad provides the essential support for a tower crane. The base is connected to a tower or a mast and stabilizes the crane that is attached to the inside of the structure of the building. Usually, this attachment point is to an elevator shaft or to a concrete lift.
The crane's mast is normally a triangulated lattice structure which measures 10 feet square or 0.9m2. Attached 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 may have a max unsupported height of 80m or 265 feet, while the minimum lifting capacity of a tower crane is 16,642 kg or 39,690 pounds with counter weights of 20 tons. Moreover, two limit switches are used to be able to ensure the driver does not overload the crane. There is also another safety feature referred to as a load moment switch to ensure that the driver does not exceed the ton meter load rating. Lastly, the tower crane has a maximum reach of 70 meters or 230 feet.
Because of 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 location by using a large tractor-trailer rig setup. After that, a mobile crane is utilized so as to assemble the machinery part of the crane and the jib. After that, these sections are attached to the mast. Then, the mobile crane adds counterweights. Crawler cranes and forklifts can be some of the other industrial machinery which is commonly used to erect a crane.
Mast extensions are added to the crane as the building is erected. This is how the height of the crane can 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 could detach from the top of the mast. In the top climber, hydraulic rams are used to adjust the slewing unit up an additional 6.1m or 20 feet. Then, the crane driver utilizes the crane to insert and bolt into place another mast section piece.