The base of the tower crane is typically bolted to a large concrete pad that provides very crucial support. The base is connected to a mast or a tower and stabilizes the crane which 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.
Generally, the mast is a triangulated lattice structure measuring 0.9m2 or 10 feet square. The slewing unit is connected to the very top of the mast. The slewing unit is made of a gear and a motor which enable 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 kg or 39,690 lbs. with counter weights of 20 tons. In addition, two limit switches are utilized in order to make certain that the operator does not overload the crane. There is also one more safety feature known as a load moment switch to make sure that the driver does not exceed the ton meter load rating. Finally, the maximum reach of a tower crane is 230 feet or 70 meters.
Due to their extreme heights, there is a science involved to erecting a crane. The stationary structure would first have to be transported to the construction location by using a big tractor-trailer rig setup. After that, a mobile crane is used so as to assemble the machine portion of the jib and the crane. Afterwards, these parts are connected to the mast. The mobile crane then adds counterweights. Crawler cranes and forklifts could be some of the other industrial machinery that is used to erect a crane.
Mast extensions are added to the crane as the building is erected. This is how the height of the crane is able to match the building's height. The crane crew uses what is referred to 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 in order 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 6.1m or 20 feet. After that, the operator of the crane utilizes the crane to insert and bolt into position one more mast section piece.