The tower crane's base is usually bolted to a large concrete pad that provides really crucial support. The base is connected to a mast or a tower and stabilizes the crane which is connected to the inside of the building's structure. Normally, this attachment point is to an elevator shaft or to a concrete lift.
The mast of the crane is usually 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 is made of a motor and a gear that enable the crane to rotate.
Tower cranes may have a max unsupported height of 80m or 265 feet, while the minimum lifting capacity of a tower crane is 16,642 kilograms or 39,690 pounds with counter weights of 20 tons. In addition, two limit switches are used in order to make certain that the operator does not overload the crane. There is even another safety feature called a load moment switch to make certain that the driver does not surpass the ton meter load rating. Finally, the maximum reach of a tower crane is 230 feet or 70 meters.
There is definitely a science involved with erecting a tower crane, especially due to their extreme heights. At first, the stationary structure has to be brought to the construction site by using a huge tractor-trailer rig setup. After that, a mobile crane is utilized so as to assemble the machinery portion of the jib and the crane. Afterwards, these parts are connected to the mast. The mobile crane next adds counterweights. Forklifts and crawler cranes could be some 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 utilizes what is called a top climber or a climbing frame 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 utilized to adjust the slewing unit up an extra 20 feet or 6.1m. Then, the driver of the crane utilizes the crane to insert and bolt into place another mast part piece.