Usually the base which is bolted into a big concrete pad provides the crucial 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. Usually, this attachment point is to a concrete lift or to an elevator shaft.
The crane's mast is usually 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 allows 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 kilograms or 39,690 lbs. with counter weights of 20 tons. In addition, two limit switches are used in order to ensure the driver does not overload the crane. There is also 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 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 would first have to be transported to the construction site by using a huge tractor-trailer rig setup. Then, a mobile crane is utilized so as to assemble the equipment portion of the crane and the jib. These parts are then attached to the mast. Afterward, the mobile crane adds counterweights. Crawler cranes and forklifts can be a few of the other industrial machinery which is 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 is able to match the building's height. The crane crew uses what is known as a top climber or a climbing frame which fits between the top of the mast and the slewing unit. A weight is hung on the jib by the work crew so as to balance the counterweight. When complete, the slewing unit is able to 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 operator uses the crane to insert and bolt into position one more mast part piece.