Typically the base that is bolted into a large concrete pad provides the necessary support for a tower crane. The base is connected to a tower or a mast and stabilizes the crane which is affixed to the inside of the structure of the building. Normally, this attachment point is to an elevator shaft or to a concrete lift.
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. Moreover, two limit switches are utilized to be able to ensure the driver does not overload the crane. There is also another safety feature called 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.
There is certainly a science involved with erecting a tower crane, specially due to their extreme heights. At first, the stationary structure has to be transported to the construction site by using a huge tractor-trailer rig setup. Next, a mobile crane is used so as to assemble the equipment part of the crane and the jib. These sections are then attached to the mast. The mobile crane then adds counterweights. Crawler cranes and forklifts can be some of the other industrial machines that is typically utilized to erect a crane.
As the building is erected, mast extensions are added to the crane. This is how the crane's height could match the building's height. The crane crew uses what is known as 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 in order to balance the counterweight. Once complete, the slewing unit could 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. Next, the crane operator uses the crane to insert and bolt into place another mast part piece.