Usually the base which is bolted into a huge concrete pad provides the necessary support for a tower crane. The base is connected to a tower or a mast and stabilizes the crane which is attached to the inside of the structure of the building. Usually, this attachment point is to a concrete lift or to an elevator shaft.
The crane's mast is often a triangulated lattice structure which 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 enable the crane to rotate.
Tower cranes may have a max unsupported height of 80m or 265 feet, while the tower crane's maximum lifting capacity is 16,642 kg or 39,690 pounds with counter weights of 20 tons. In addition, two limit switches are utilized in order to ensure the operator does not overload the crane. There is also another safety feature called a load moment switch to ensure that the operator does not surpass the ton meter load rating. Lastly, the tower crane has a maximum reach of 70 meters or 230 feet.
Due to their extreme heights, there is a science involved to erecting a crane. The stationary structure will first have to be brought to the construction location by utilizing a large tractor-trailer rig setup. Next, a mobile crane is used in order to assemble the machine portion of the crane and the jib. These parts are then connected to the mast. The mobile crane then adds counterweights. Forklifts and crawler cranes may be some of the other industrial machinery which is 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 utilizes what is called 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 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 utilized to adjust the slewing unit up an extra 6.1m or 20 feet. Then, the operator of the crane uses the crane to insert and bolt into place one more mast section piece.