Generally the base which 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 connected to the inside of the building's structure. Often, this attachment point is to a concrete lift or to an elevator shaft.
The mast of the crane is usually a triangulated lattice structure that measures 10 feet square or 0.9m2. 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 kg or 39,690 lbs. with counter weights of 20 tons. Additionally, two limit switches are utilized to be able to make sure that the driver does not overload the crane. There is also one more 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 70 meters or 230 feet.
There is definitely a science involved with erecting a tower crane, especially because of their extreme heights. First, the stationary structure needs to be transported to the construction site by using a large tractor-trailer rig setup. Then, a mobile crane is used in order to assemble the machine part of the jib and the crane. These sections are then attached to the mast. Then, the mobile crane adds counterweights. Crawler cranes and forklifts may be some of the other industrial machines which is commonly 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 known as a climbing frame or a top climber which 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. When complete, the slewing unit can detach from the top of the mast. In the top climber, hydraulic rams are utilized to adjust the slewing unit up an additional 6.1m or 20 feet. After that, the crane operator utilizes the crane to insert and bolt into place another mast part piece.