The tower crane's base is generally bolted to a large concrete pad which provides very crucial support. The base is connected to a mast or a tower and stabilizes the crane which is affixed to the inside of the building's structure. Usually, this attachment point is to a concrete lift or to an elevator shaft.
Usually, the mast is a triangulated lattice structure measuring 0.9m2 or 10 feet square. The slewing unit is connected to the very top of the mast. The slewing unit consists of a gear and a motor which enable 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 pounds with counter weights of 20 tons. Furthermore, two limit switches are utilized in order to ensure the driver does not overload the crane. There is even another safety feature called a load moment switch to make sure that the operator does not surpass the ton meter load rating. Last of all, the tower crane has a maximum reach of 70 meters or 230 feet.
There is definitely a science involved with erecting a tower crane, specially because of their extreme heights. At first, the stationary structure needs to be transported to the construction location by utilizing a huge tractor-trailer rig setup. After that, a mobile crane is used so as to assemble the equipment part of the jib and the crane. Afterwards, these parts are connected to the mast. The mobile crane then adds counterweights. Forklifts and crawler cranes can be a few of the other industrial machinery which is usually utilized to erect a crane.
Mast extensions are added to the crane as the building is erected. This is how the height of the crane can match the building's height. The crane crew uses what is called 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 in order to balance the counterweight. Once complete, the slewing unit is able to detach from the top of the mast. In the top climber, hydraulic rams are utilized to adjust the slewing unit up an extra 6.1m or 20 feet. Then, the crane driver uses the crane to insert and bolt into place another mast section piece.