Usually the base that is bolted into a huge concrete pad provides the essential support for a tower crane. The base is attached to a mast or a tower and stabilizes the crane which is affixed to the inside of the structure of the building. Often, this attachment point is to an elevator shaft or to a concrete lift.
The crane's mast is often a triangulated lattice structure which 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 which allows 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. Moreover, two limit switches are utilized in order to ensure the driver does not overload the crane. There is also another safety feature called a load moment switch to ensure that the operator does not surpass the ton meter load rating. Lastly, the maximum reach of a tower crane is 230 feet or 70 meters.
Because of their extreme heights, there is a science involved to erecting a crane. The stationary structure would at first need to be brought to the construction location by utilizing a large tractor-trailer rig setup. Then, a mobile crane is used in order to assemble the equipment portion of the crane and the jib. These sections are then attached to the mast. Then, the mobile crane adds counterweights. Forklifts and crawler cranes could be a few of the other industrial machines that is usually used to erect a crane.
When 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 uses what is referred to 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 6.1m or 20 feet. Then, the crane driver utilizes the crane to insert and bolt into place one more mast part piece.