The base of the tower crane is generally bolted to a big concrete pad which provides really necessary support. The base is attached to a mast or a tower and stabilizes the crane that 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 often a triangulated lattice structure which measures 0.9m2 or 10 feet square. Attached to the very top of the mast is the slewing unit. The slewing unit is made of a gear and a motor 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 kilograms or 39,690 lbs. with counter weights of 20 tons. Additionally, 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 make sure that the driver does not exceed the ton meter load rating. Last of all, the maximum reach of a tower crane is 70 meters or 230 feet.
There is definitely a science involved with erecting a tower crane, particularly due to their extreme heights. At first, the stationary structure needs to be transported to the construction location by utilizing a big tractor-trailer rig setup. Then, a mobile crane is used so as to assemble the machinery part of the crane and the jib. After that, these parts are attached to the mast. Afterward, the mobile crane adds counterweights. Forklifts and crawler cranes may be some of the other industrial machinery which is typically utilized 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 uses 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 in order to balance the counterweight. When complete, the slewing unit could detach from the top of the mast. In the top climber, hydraulic rams are utilized to adjust the slewing unit up an additional 20 feet or 6.1m. Then, the crane driver uses the crane to insert and bolt into place another mast section piece.