The tower crane's base is usually bolted to a large concrete pad that provides very necessary support. The base is attached to a tower or a mast and stabilizes the crane that is attached to the inside of the building's structure. Normally, this attachment point is to a concrete lift or to an elevator shaft.
The crane's mast is normally 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 motor and a gear which 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 lbs. with counter weights of 20 tons. Furthermore, two limit switches are used to be able to ensure the operator does not overload the crane. There is even another safety feature referred to as a load moment switch to ensure that the driver does not surpass the ton meter load rating. Lastly, 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 because of their extreme heights. First, the stationary structure has to be brought 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 sections are then attached to the mast. The mobile crane next adds counterweights. Forklifts and crawler cranes could be some of the other industrial equipment which is typically used to erect a crane.
When the building is erected, mast extensions are added to the crane. This is how the crane's height can match the building's height. The crane crew uses 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 in order to balance the counterweight. Once 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 20 feet or 6.1m. Next, the crane driver uses the crane to insert and bolt into position one more mast part piece.