Generally the base that is bolted into a big concrete pad provides the essential support for a tower crane. The base is connected to a tower or a mast and stabilizes the crane which is attached to the inside of the building's structure. Often, this attachment point is to a concrete lift or to an elevator shaft.
The crane's mast is normally a triangulated lattice structure that measures 10 feet square or 0.9m2. Connected to the very top of the mast is the slewing unit. The slewing unit consists of a gear and a motor which allows the crane to rotate.
Tower cranes are able to have a maximum unsupported height of 80m or 265 feet. The tower crane's maximum lifting capacity is 16,642 kilograms or 39,690 lbs. with counter weights of 20 tons. Additionally, two limit switches are used in order to make sure that the operator does not overload the crane. There is also another safety feature known as a load moment switch to ensure that the driver does not surpass the ton meter load rating. Lastly, the tower crane has a maximum reach of 230 feet or 70 meters.
There is definitely a science involved with erecting a tower crane, specially due to their extreme heights. First, the stationary structure needs to be brought to the construction site by utilizing a huge tractor-trailer rig setup. Then, a mobile crane is used so as to assemble the machinery 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 some of the other industrial machines which is typically utilized to erect a crane.
When the building is erected, mast extensions are added to the crane. This is how the crane's height could match the building's height. The crane crew utilizes 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 so as to balance the counterweight. When 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 additional 6.1m or 20 feet. After that, the operator of the crane uses the crane to insert and bolt into position another mast part piece.