Typically the base which 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 an elevator shaft or to a concrete lift.
Usually, 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 that enable 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 kilograms or 39,690 pounds with counter weights of 20 tons. Moreover, two limit switches are utilized to be able to make certain that 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 operator does not exceed the ton meter load rating. Lastly, the tower crane has a maximum reach of 230 feet or 70 meters.
Due to their extreme heights, there is a science involved to erecting a crane. The stationary structure would at first need to be brought to the construction location by using a large tractor-trailer rig setup. Next, a mobile crane is used in order to assemble the machinery portion of the crane and the jib. These parts are then connected to the mast. The mobile crane then adds counterweights. Forklifts and crawler cranes may be some of the other industrial equipment that is 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 can match the building's height. The crane crew utilizes what is known as a climbing frame or a top climber 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 is able to detach from the top of the mast. In the top climber, hydraulic rams are used to adjust the slewing unit up an additional 20 feet or 6.1m. Then, the driver of the crane utilizes the crane to insert and bolt into place one more mast section piece.