The tower crane's base is generally bolted to a large concrete pad that provides very crucial support. 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. Normally, this attachment point is to an elevator shaft or to a concrete lift.
The mast of the crane is normally a triangulated lattice structure that measures 0.9m2 or 10 feet square. Attached to the very top of the mast is the slewing unit. The slewing unit consists 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 tower crane's maximum lifting capacity is 16,642 kg or 39,690 lbs. with counter weights of 20 tons. Additionally, two limit switches are used in order to make certain that the driver does not overload the crane. There is even another safety feature called a load moment switch to ensure that the operator does not exceed the ton meter load rating. Lastly, the maximum reach of a tower crane is 230 feet or 70 meters.
Due to their extreme heights, there is a science involved to erecting a crane. The stationary structure would first have to be brought to the construction site by using a huge tractor-trailer rig setup. Then, a mobile crane is utilized in order to assemble the machinery part of the crane and the jib. Afterwards, these parts are attached to the mast. The mobile crane then adds counterweights. Crawler cranes and forklifts could be some of the other industrial equipment that 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 could match the building's height. The crane crew utilizes what is known as a climbing frame or a top climber that fits between the top of the mast and the slewing unit. A weight is hung on the jib by the work crew so as 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 used to adjust the slewing unit up an extra 20 feet or 6.1m. Next, the crane driver uses the crane to insert and bolt into position another mast part piece.