The tower crane's base is generally bolted to a big concrete pad which provides very crucial support. The base is attached to a mast or a tower and stabilizes the crane which is attached to the inside of the structure of the building. Usually, 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 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 which 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 kilograms or 39,690 pounds with counter weights of 20 tons. Furthermore, two limit switches are utilized in order to ensure the operator does not overload the crane. There is even one more safety feature called a load moment switch to ensure that the operator does not exceed the ton meter load rating. Lastly, the tower crane has a maximum reach of 230 feet or 70 meters.
There is definitely a science involved with erecting a tower crane, specially because of their extreme heights. First, the stationary structure has to be transported to the construction site by utilizing a large tractor-trailer rig setup. After that, a mobile crane is used in order to assemble the machine portion of the jib and the crane. After that, these parts are connected to the mast. The mobile crane then adds counterweights. Forklifts and crawler cranes could be some of the other industrial equipment that is 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 that 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 can detach from the top of the mast. In the top climber, hydraulic rams are used to adjust the slewing unit up an extra 20 feet or 6.1m. After that, the driver of the crane uses the crane to insert and bolt into position one more mast section piece.