Usually the base that is bolted into a huge concrete pad provides the essential support for a tower crane. The base is connected to a mast or a tower and stabilizes the crane that is connected to the inside of the building's structure. Normally, this attachment point is to an elevator shaft or to a concrete lift.
Typically, 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 consists of a motor and a gear that 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 kilograms or 39,690 lbs. with counter weights of 20 tons. Additionally, two limit switches are utilized to be able to make certain that the driver does not overload the crane. There is also one more safety feature known as 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.
There is certainly a science involved with erecting a tower crane, especially because of their extreme heights. At first, the stationary structure has to be brought to the construction site by utilizing a large tractor-trailer rig setup. Then, a mobile crane is utilized so as to assemble the machinery portion of the crane and the jib. These sections are then connected to the mast. The mobile crane then adds counterweights. Forklifts and crawler cranes may be a few of the other industrial machinery which is utilized 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 known as a top climber or a climbing frame 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 can detach from the top of the mast. In the top climber, hydraulic rams are utilized to adjust the slewing unit up an extra 20 feet or 6.1m. Next, the crane driver utilizes the crane to insert and bolt into position another mast section piece.