Generally the base that is bolted into a huge concrete pad provides the crucial support for a tower crane. The base is attached to a tower or a mast and stabilizes the crane that is affixed to the inside of the structure of the building. Often, 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 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 are able to have a maximum unsupported height of 80m or 265 feet. The maximum lifting capacity of a tower crane is 16,642 kg or 39,690 lbs. with counter weights of 20 tons. In addition, two limit switches are utilized to be able to make certain that the operator does not overload the crane. There is even 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 tower crane has a maximum reach of 70 meters or 230 feet.
Because of their extreme heights, there is a science involved to erecting a crane. The stationary structure will first need to be brought to the construction site by utilizing a huge tractor-trailer rig setup. Next, a mobile crane is utilized so as to assemble the machinery part of the jib and the crane. After that, these sections are connected to the mast. The mobile crane then adds counterweights. Crawler cranes and forklifts may be some of the other industrial machinery that 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 is able to match the building's height. The crane crew utilizes what is called 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 so as to balance the counterweight. Once complete, the slewing unit can detach from the top of the mast. In the top climber, hydraulic rams are used to adjust the slewing unit up an extra 6.1m or 20 feet. After that, the crane driver uses the crane to insert and bolt into place one more mast part piece.