The base of the tower crane is typically bolted to a big concrete pad that provides very crucial support. The base is attached to a tower or a mast and stabilizes the crane which is attached 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 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 kg 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 called a load moment switch to ensure that the operator does not surpass the ton meter load rating. Lastly, the tower crane has a maximum reach of 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 needs to be brought to the construction site by utilizing a big tractor-trailer rig setup. Then, a mobile crane is utilized so as to assemble the machinery part of the jib and the crane. Afterwards, these sections are connected to the mast. Next, the mobile crane adds counterweights. Crawler cranes and forklifts may be some of the other industrial machines that is commonly utilized to erect a crane.
Mast extensions are added to the crane when the building is erected. This is how the height of the crane is able to match the building's height. The crane crew uses what is known 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. Once 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 extra 20 feet or 6.1m. Next, the crane operator uses the crane to insert and bolt into place another mast section piece.