The base of the tower crane is typically bolted to a huge concrete pad which provides really crucial support. The base is connected to a tower or a mast and stabilizes the crane which is attached 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 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 gear and a motor which enable 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 pounds with counter weights of 20 tons. Additionally, two limit switches are used to be able to ensure the operator does not overload the crane. There is even one more safety feature called a load moment switch to ensure that the driver does not surpass the ton meter load rating. Finally, the maximum reach of a tower crane is 70 meters or 230 feet.
There is certainly a science involved with erecting a tower crane, especially because of their extreme heights. First, the stationary structure needs to be transported to the construction site by utilizing a huge tractor-trailer rig setup. Then, a mobile crane is utilized in order to assemble the machinery portion of the jib and the crane. Afterwards, these parts are connected to the mast. Afterward, the mobile crane adds counterweights. Forklifts and crawler cranes could be some of the other industrial machines that is 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 could match the building's height. The crane crew utilizes what is called a climbing frame or a top climber 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. When 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. After that, the operator of the crane utilizes the crane to insert and bolt into position another mast section piece.