Generally the base which is bolted into a large concrete pad provides the necessary support for a tower crane. The base is connected to a mast or a tower and stabilizes the crane that is connected to the inside of the building's structure. Often, this attachment point is to an elevator shaft or to a concrete lift.
The crane's mast is often 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 tower crane's maximum lifting capacity is 16,642 kg or 39,690 pounds with counter weights of 20 tons. Furthermore, two limit switches are used in order to ensure the driver does not overload the crane. There is even another safety feature called a load moment switch to make sure that the operator does not surpass the ton meter load rating. Last of all, the tower crane has a maximum reach of 70 meters or 230 feet.
There is certainly a science involved with erecting a tower crane, especially due to their extreme heights. At first, the stationary structure needs to be transported to the construction location by utilizing a large tractor-trailer rig setup. Then, a mobile crane is used in order to assemble the machinery part of the crane and the jib. After that, these sections are attached to the mast. The mobile crane then adds counterweights. Forklifts and crawler cranes can be some of the other industrial machinery that is usually used to erect a crane.
When the building is erected, mast extensions are added to the crane. This is how the crane's height is able to match the building's height. The crane crew uses what is called a climbing frame or a top climber that 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 20 feet or 6.1m. After that, the crane operator utilizes the crane to insert and bolt into place one more mast section piece.