Usually the base which is bolted into a large concrete pad provides the necessary support for a tower crane. The base is attached to a mast or a tower and stabilizes the crane which is attached to the inside of the structure of the building. Normally, this attachment point is to an elevator shaft or to a concrete lift.
The mast of the crane is often 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 is made 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 kilograms or 39,690 lbs. with counter weights of 20 tons. Moreover, 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 make certain that the operator does not exceed the ton meter load rating. Last of all, the tower crane has a maximum reach of 70 meters or 230 feet.
There is definitely a science involved with erecting a tower crane, specially due to their extreme heights. First, the stationary structure needs to be transported to the construction site by using a large tractor-trailer rig setup. Next, a mobile crane is utilized in order to assemble the machine part of the crane and the jib. Afterwards, these parts are connected to the mast. The mobile crane next adds counterweights. Forklifts and crawler cranes could be some of the other industrial equipment which is utilized 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 utilizes what is called 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. When 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 additional 20 feet or 6.1m. Next, the crane operator uses the crane to insert and bolt into place one more mast part piece.