The base of the tower crane is usually bolted to a large concrete pad which provides really necessary support. The base is attached to a tower or a mast and stabilizes the crane that 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.
Generally, the mast is a triangulated lattice structure measuring 0.9m2 or 10 feet square. The slewing unit is connected to the very top of the mast. The slewing unit consists of a motor and a gear which enable the crane to rotate.
Tower cranes may have a max unsupported height of 80m or 265 feet, while the minimum 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 used to be able to make certain that the operator does not overload the crane. There is even another safety feature referred to as a load moment switch to make sure that the driver does not exceed the ton meter load rating. Lastly, the maximum reach of a tower crane is 70 meters or 230 feet.
There is certainly a science involved with erecting a tower crane, specially due to their extreme heights. First, the stationary structure needs to be brought to the construction site by using a large tractor-trailer rig setup. Then, a mobile crane is utilized so as to assemble the machine portion of the crane and the jib. After that, these sections are attached to the mast. The mobile crane next adds counterweights. Crawler cranes and forklifts may be some of the other industrial machines that is used to erect a crane.
Mast extensions are added to the crane when the building is erected. This is how the height of the crane is able to match the building's height. The crane crew utilizes what is called a climbing frame or a top climber 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. 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 6.1m or 20 feet. After that, the crane driver uses the crane to insert and bolt into place another mast part piece.