Generally the base that is bolted into a huge 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. Usually, this attachment point is to an elevator shaft or to a concrete lift.
The crane's mast is usually a triangulated lattice structure that measures 10 feet square or 0.9m2. Attached to the very top of the mast is the slewing unit. The slewing unit consists of a motor and a gear that allows the crane to rotate.
Tower cranes may have a max unsupported height of 80m or 265 feet, while the tower crane's maximum lifting capacity is 16,642 kg or 39,690 lbs. with counter weights of 20 tons. Moreover, two limit switches are used in order to make sure that 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 tower crane has a maximum reach of 230 feet or 70 meters.
There is definitely a science involved with erecting a tower crane, especially due to their extreme heights. First, the stationary structure has to be transported to the construction location by utilizing a huge tractor-trailer rig setup. Then, a mobile crane is used in order to assemble the machine part of the jib and the crane. These parts are then attached to the mast. After that, the mobile crane adds counterweights. Crawler cranes and forklifts could be some of the other industrial machinery which is typically used to erect a crane.
As 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 referred to as 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. 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 additional 20 feet or 6.1m. Then, the operator of the crane utilizes the crane to insert and bolt into place another mast part piece.