Usually the base that is bolted into a big concrete pad provides the necessary support for a tower crane. The base is attached to a tower or a mast and stabilizes the crane which is affixed to the inside of the building's structure. Usually, this attachment point is to an elevator shaft or to a concrete lift.
Usually, the mast is a triangulated lattice structure measuring 10 feet square or 0.9m2. The slewing unit is attached to the very top of the mast. The slewing unit consists of a motor and a gear 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 lbs. 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 referred to as a load moment switch to make sure that the operator does not surpass the ton meter load rating. Lastly, the maximum reach of a tower crane is 70 meters or 230 feet.
There is definitely a science involved with erecting a tower crane, specially due to their extreme heights. First, the stationary structure has to be brought to the construction location by using a large tractor-trailer rig setup. Then, a mobile crane is used so as to assemble the machine part of the crane and the jib. These parts are then connected to the mast. Afterward, the mobile crane adds counterweights. Crawler cranes and forklifts may be a few of the other industrial machinery which 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 referred to as a top climber or a climbing frame that 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. When complete, the slewing unit could 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 utilizes the crane to insert and bolt into position one more mast section piece.