Generally the base that is bolted into a huge concrete pad provides the crucial support for a tower crane. The base is connected to a tower or a mast and stabilizes the crane that is attached to the inside of the building's structure. Often, this attachment point is to an elevator shaft or to a concrete lift.
The mast of the crane is often a triangulated lattice structure which measures 0.9m2 or 10 feet square. Attached to the very top of the mast is the slewing unit. The slewing unit is made 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 kg or 39,690 lbs. with counter weights of 20 tons. Moreover, two limit switches are utilized in order to ensure the operator does not overload the crane. There is also one more safety feature called a load moment switch to ensure that the operator does not surpass the ton meter load rating. Finally, 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 transported to the construction site by using a huge tractor-trailer rig setup. Then, a mobile crane is utilized so as to assemble the machine portion of the jib and the crane. After that, these sections are connected to the mast. The mobile crane next adds counterweights. Forklifts and crawler cranes can be a few of the other industrial equipment that is typically utilized to erect a crane.
As 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 uses what is called 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 in order 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 extra 20 feet or 6.1m. After that, the driver of the crane uses the crane to insert and bolt into place one more mast section piece.