Typically the base which is bolted into a big concrete pad provides the essential support for a tower crane. The base is connected to a tower or a mast and stabilizes the crane which is connected to the inside of the building's structure. Usually, this attachment point is to a concrete lift or to an elevator shaft.
The mast of the crane is usually a triangulated lattice structure that measures 10 feet square or 0.9m2. Connected to the very top of the mast is the slewing unit. The slewing unit consists of a motor and a gear that enable the crane to rotate.
Tower cranes are able to have a maximum unsupported height of 80m or 265 feet. The maximum lifting capacity of a tower crane is 16,642 kilograms or 39,690 lbs. with counter weights of 20 tons. In addition, two limit switches are used in order to make sure that 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 surpass the ton meter load rating. Lastly, the maximum reach of a tower crane is 70 meters or 230 feet.
Due to their extreme heights, there is a science involved to erecting a crane. The stationary structure will first have to be brought to the construction location by using a large tractor-trailer rig setup. After that, a mobile crane is used in order to assemble the machinery part of the jib and the crane. These sections are then attached to the mast. Then, the mobile crane adds counterweights. Crawler cranes and forklifts could be some of the other industrial machinery that is usually utilized to erect a crane.
As 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 referred to as 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 so as to balance the counterweight. When complete, the slewing unit could 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 driver of the crane uses the crane to insert and bolt into position one more mast part piece.