Usually the base that is bolted into a huge concrete pad provides the necessary support for a tower crane. The base is connected to a mast or a tower and stabilizes the crane that is attached to the inside of the building's structure. Often, this attachment point is to a concrete lift or to an elevator shaft.
Generally, the mast is a triangulated lattice structure measuring 10 feet square or 0.9m2. The slewing unit is attached to the very top of the mast. The slewing unit is made of a gear and a motor which allows the crane to rotate.
Tower cranes are able to have a maximum unsupported height of 80m or 265 feet. The tower crane's maximum lifting capacity is 16,642 kg or 39,690 pounds with counter weights of 20 tons. Additionally, two limit switches are utilized to be able to ensure the driver does not overload the crane. There is also one more safety feature called a load moment switch to make certain that the driver does not exceed the ton meter load rating. Finally, 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. At first, the stationary structure has to be brought to the construction location by utilizing a large tractor-trailer rig setup. Next, a mobile crane is used in order to assemble the machinery portion of the crane and the jib. These sections are then attached to the mast. The mobile crane then adds counterweights. Forklifts and crawler cranes could be some of the other industrial machinery that 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 is able to match the building's height. The crane crew uses what is called a top climber or a climbing frame that 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 used to adjust the slewing unit up an extra 20 feet or 6.1m. Then, the crane operator utilizes the crane to insert and bolt into place another mast part piece.