The base of the tower crane is typically bolted to a large concrete pad which provides very necessary 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. Normally, this attachment point is to an elevator shaft or to a concrete lift.
Generally, 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 which allows the crane to rotate.
Tower cranes may have a max unsupported height of 80m or 265 feet, while the tower crane's maximum lifting capacity is 16,642 kilograms or 39,690 lbs. with counter weights of 20 tons. Furthermore, two limit switches are used in order to ensure the operator does not overload the crane. There is even another safety feature referred to as a load moment switch to make sure that the driver does not surpass the ton meter load rating. Finally, the tower crane has a maximum reach of 70 meters or 230 feet.
There is certainly a science involved with erecting a tower crane, specially because of their extreme heights. At first, the stationary structure has to be brought to the construction site by using a large tractor-trailer rig setup. Next, a mobile crane is utilized in order to assemble the machine portion of the crane and the jib. These sections are then attached to the mast. The mobile crane then adds counterweights. Crawler cranes and forklifts may be a few of the other industrial machines which is usually 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 could 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 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. 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 additional 6.1m or 20 feet. After that, the crane driver uses the crane to insert and bolt into position one more mast section piece.