The tower crane's base is generally bolted to a large concrete pad which provides really crucial support. The base is attached to a tower or a mast and stabilizes the crane that is affixed to the inside of the building's structure. Normally, this attachment point is to a concrete lift or to an elevator shaft.
The crane's mast is often 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 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 utilized to be able to make certain that the operator does not overload the crane. There is even another safety feature known as a load moment switch to ensure that the driver does not surpass the ton meter load rating. Finally, the tower crane has a maximum reach of 230 feet or 70 meters.
There is definitely a science involved with erecting a tower crane, especially due to their extreme heights. First, the stationary structure needs to be transported to the construction location by using a huge tractor-trailer rig setup. Next, a mobile crane is utilized so as to assemble the machinery portion of the crane and the jib. These sections are then connected to the mast. The mobile crane next adds counterweights. Crawler cranes and forklifts could be some of the other industrial equipment that is 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 can match the building's height. The crane crew utilizes 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. When 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 extra 20 feet or 6.1m. Next, the crane operator uses the crane to insert and bolt into place another mast part piece.