The tower crane's base is generally bolted to a huge concrete pad that provides very necessary support. The base is connected to a mast or a tower and stabilizes the crane which is attached to the inside of the structure of the building. Often, this attachment point is to an elevator shaft or to a concrete lift.
The crane's mast is usually 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 consists of a gear and a motor that 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 kg or 39,690 lbs. with counter weights of 20 tons. In addition, two limit switches are used in order to make sure that the driver does not overload the crane. There is even one more safety feature called a load moment switch to ensure 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.
Due to their extreme heights, there is a science involved to erecting a crane. The stationary structure would at first have to be transported to the construction location by utilizing a huge tractor-trailer rig setup. Next, a mobile crane is used in order to assemble the machinery portion of the crane and the jib. These sections are then attached to the mast. Then, the mobile crane adds counterweights. Crawler cranes and forklifts can be some of the other industrial equipment 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 could match the building's height. The crane crew uses what is known as a top climber or a climbing frame which fits between the slewing unit and the top of the mast. A weight is hung on the jib by the work crew in order to balance the counterweight. Once 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 extra 6.1m or 20 feet. Next, the crane operator uses the crane to insert and bolt into position one more mast section piece.