Typically the base that is bolted into a big concrete pad provides the essential support for a tower crane. The base is connected to a mast or a tower and stabilizes the crane which is affixed 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 that measures 10 feet square or 0.9m2. 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 tower crane's maximum lifting capacity is 16,642 kg or 39,690 lbs. 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 even one more safety feature called a load moment switch to make certain that the operator does not surpass the ton meter load rating. Lastly, 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 because of their extreme heights. At first, the stationary structure has to be transported to the construction site by using a huge tractor-trailer rig setup. Then, a mobile crane is used so as to assemble the machinery part of the crane and the jib. Afterwards, these sections are attached to the mast. The mobile crane next adds counterweights. Forklifts and crawler cranes can be some of the other industrial equipment which is utilized to erect a crane.
When the building is erected, mast extensions are added to the crane. This is how the crane's height could match the building's height. The crane crew uses what is called a top climber or a climbing frame which fits between the top of the mast and the slewing unit. A weight is hung on the jib by the work crew so as to balance the counterweight. Once complete, the slewing unit can 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 operator utilizes the crane to insert and bolt into position another mast section piece.