The base of the tower crane is typically bolted to a large concrete pad that provides very crucial support. The base is attached to a tower or a mast and stabilizes the crane which is connected to the inside of the structure of the building. Usually, 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 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 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 known as a load moment switch to ensure that the driver does not exceed the ton meter load rating. Lastly, the maximum reach of a tower crane is 230 feet or 70 meters.
There is definitely a science involved with erecting a tower crane, specially due to their extreme heights. At first, the stationary structure needs to be transported to the construction site by utilizing a huge tractor-trailer rig setup. Next, a mobile crane is utilized in order to assemble the equipment part of the crane and the jib. These parts are then connected to the mast. The mobile crane then adds counterweights. Crawler cranes and forklifts could be some of the other industrial equipment which is usually 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 called 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 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 6.1m or 20 feet. Then, the driver of the crane utilizes the crane to insert and bolt into position one more mast section piece.