Usually the base which is bolted into a huge concrete pad provides the crucial support for a tower crane. The base is connected to a tower or a mast and stabilizes the crane which is affixed to the inside of the building's structure. Often, this attachment point is to an elevator shaft or to a concrete lift.
The mast of the crane is normally a triangulated lattice structure that 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 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 kilograms or 39,690 pounds with counter weights of 20 tons. Moreover, two limit switches are used in order to ensure the driver 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. Lastly, the tower crane has a maximum reach of 230 feet or 70 meters.
There is certainly a science involved with erecting a tower crane, particularly due to their extreme heights. First, the stationary structure needs to be transported to the construction site by utilizing a big tractor-trailer rig setup. Next, a mobile crane is used in order to assemble the machine portion of the crane and the jib. Then, these parts are attached to the mast. The mobile crane next adds counterweights. Crawler cranes and forklifts can be some of the other industrial equipment which is usually 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 is able to match the building's height. The crane crew uses what is known as a top climber or a climbing frame that 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 can detach from the top of the mast. In the top climber, hydraulic rams are used to adjust the slewing unit up an extra 6.1m or 20 feet. After that, the crane driver utilizes the crane to insert and bolt into position one more mast section piece.