The base of the tower crane is usually bolted to a large concrete pad that provides very necessary support. The base is attached to a mast or a tower and stabilizes the crane which is affixed to the inside of the building's structure. Often, this attachment point is to a concrete lift or to an elevator shaft.
The mast of the crane is normally 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 enable 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. In addition, two limit switches are used in order to ensure the operator does not overload the crane. There is even one more safety feature called a load moment switch to ensure that the driver does not exceed the ton meter load rating. Finally, the tower crane has a maximum reach of 230 feet or 70 meters.
Because of their extreme heights, there is a science involved to erecting a crane. The stationary structure will first have to be brought to the construction site by utilizing a huge tractor-trailer rig setup. Next, a mobile crane is utilized in order to assemble the machine part of the crane and the jib. Afterwards, these sections are connected to the mast. The mobile crane next adds counterweights. Crawler cranes and forklifts can be a few of the other industrial machines which is usually used to erect a crane.
As the building is erected, mast extensions are added to the crane. This is how the crane's height can match the building's height. The crane crew uses what is known as a top climber or a climbing frame that fits between the top of the mast and the slewing unit. A weight is hung on the jib by the work crew in order to balance the counterweight. When complete, the slewing unit could detach from the top of the mast. In the top climber, hydraulic rams are utilized to adjust the slewing unit up an additional 20 feet or 6.1m. After that, the crane operator utilizes the crane to insert and bolt into place one more mast part piece.