The tower crane's base is generally bolted to a big concrete pad which provides very necessary support. The base is attached to a mast or a tower and stabilizes the crane which is attached to the inside of the building's structure. Usually, this attachment point is to an elevator shaft or to a concrete lift.
Generally, the mast is a triangulated lattice structure measuring 0.9m2 or 10 feet square. The slewing unit is attached to the very top of the mast. The slewing unit consists of a gear and a motor that enable 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. Additionally, two limit switches are utilized to be able to ensure the driver does not overload the crane. There is even another safety feature called a load moment switch to make certain that the operator does not exceed 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 has to be transported to the construction location by utilizing a huge tractor-trailer rig setup. Then, a mobile crane is utilized so as to assemble the equipment part of the crane and the jib. These parts are then connected to the mast. The mobile crane then adds counterweights. Crawler cranes and forklifts may be some of the other industrial machinery that is typically used to erect a crane.
As the building is erected, mast extensions are added to the crane. This is how the crane's height can match the building's height. The crane crew uses what is known as 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 in order to balance the counterweight. When complete, the slewing unit is able to detach from the top of the mast. In the top climber, hydraulic rams are used to adjust the slewing unit up an additional 6.1m or 20 feet. Next, the driver of the crane uses the crane to insert and bolt into place one more mast part piece.