The base of the tower crane is generally bolted to a huge concrete pad which provides really necessary support. The base is attached to a tower or a mast and stabilizes the crane which is affixed to the inside of the structure of the building. Often, this attachment point is to a concrete lift or to an elevator shaft.
Generally, the mast is a triangulated lattice structure measuring 0.9m2 or 10 feet square. The slewing unit is connected to the very top of the mast. The slewing unit consists 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. Furthermore, two limit switches are utilized in order to ensure the driver does not overload the crane. There is even one more safety feature called 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 first have to be transported to the construction site by utilizing a large tractor-trailer rig setup. After that, a mobile crane is used in order to assemble the equipment part of the jib and the crane. These parts are then attached to the mast. Afterward, the mobile crane adds counterweights. Crawler cranes and forklifts could be some of the other industrial machines which is typically used to erect a crane.
Mast extensions are added to the crane when the building is erected. This is how the height of the crane could match the building's height. The crane crew uses what is referred to 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 utilized to adjust the slewing unit up an extra 20 feet or 6.1m. Then, the crane driver uses the crane to insert and bolt into place another mast section piece.