The base of the tower crane is generally bolted to a big concrete pad which provides very crucial support. The base is connected to a tower or a mast and stabilizes the crane which is affixed to the inside of the structure of the building. Often, this attachment point is to a concrete lift or to an elevator shaft.
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 that 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 kilograms or 39,690 lbs. with counter weights of 20 tons. Furthermore, two limit switches are used in order to make sure that the driver does not overload the crane. There is even another safety feature called a load moment switch to make sure that the driver does not surpass the ton meter load rating. Finally, the maximum reach of a tower crane is 70 meters or 230 feet.
There is definitely a science involved with erecting a tower crane, especially because of their extreme heights. At first, the stationary structure has to be transported to the construction site by using a large tractor-trailer rig setup. After that, a mobile crane is utilized in order to assemble the machinery 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 equipment that is utilized 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 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. Once 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 20 feet or 6.1m. Then, the driver of the crane uses the crane to insert and bolt into place one more mast part piece.