The base of the tower crane is usually bolted to a big concrete pad which provides really crucial support. The base is attached to a tower or a mast and stabilizes the crane which is attached to the inside of the structure of the building. Often, this attachment point is to a concrete lift or to an elevator shaft.
Generally, 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 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. Moreover, two limit switches are used in order to make sure that the driver does not overload the crane. There is also one more safety feature called a load moment switch to ensure that the operator does not exceed the ton meter load rating. Lastly, the maximum reach of a tower crane is 70 meters or 230 feet.
There is definitely a science involved with erecting a tower crane, particularly due to their extreme heights. At first, the stationary structure needs to be transported to the construction site by using a huge tractor-trailer rig setup. After that, a mobile crane is used so as to assemble the equipment portion of the jib and the crane. These parts are then connected to the mast. The mobile crane next adds counterweights. Forklifts and crawler cranes may be a few of the other industrial machines which is typically 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 known as 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. 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 extra 6.1m or 20 feet. Then, the crane driver uses the crane to insert and bolt into place another mast section piece.