Generally the base which is bolted into a big concrete pad provides the crucial support for a tower crane. The base is attached to a mast or a tower and stabilizes the crane that is affixed to the inside of the building's structure. Normally, this attachment point is to a concrete lift or to an elevator shaft.
The crane's mast is usually 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 motor and a gear which allows 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. Furthermore, two limit switches are used in order to ensure the operator does not overload the crane. There is even another 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 230 feet or 70 meters.
There is definitely a science involved with erecting a tower crane, specially due to their extreme heights. At first, the stationary structure needs to be brought to the construction site by using a huge tractor-trailer rig setup. Next, a mobile crane is utilized in order to assemble the machinery portion of the jib and the crane. Afterwards, these parts are attached to the mast. Then, the mobile crane adds counterweights. Crawler cranes and forklifts could be some of the other industrial machines which is usually used to erect a crane.
Mast extensions are added to the crane when the building is erected. This is how the height of the crane is able to match the building's height. The crane crew utilizes what is referred to as a top climber or a climbing frame that fits between the slewing unit and the top of the mast. A weight is hung on the jib by the work crew in order to balance the counterweight. When 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 20 feet or 6.1m. After that, the driver of the crane uses the crane to insert and bolt into position one more mast section piece.