The tower crane's base is usually bolted to a huge concrete pad which provides really necessary support. The base is connected to a tower or a mast and stabilizes the crane that is connected 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 attached to the very top of the mast. The slewing unit is made of a motor and a gear that allows 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. Moreover, two limit switches are utilized to be able to ensure the driver does not overload the crane. There is even another safety feature referred to as a load moment switch to ensure that the driver does not exceed the ton meter load rating. Last of all, the maximum reach of a tower crane is 230 feet or 70 meters.
There is definitely a science involved with erecting a tower crane, especially due to their extreme heights. First, the stationary structure has to be transported to the construction site by using a big tractor-trailer rig setup. Next, a mobile crane is utilized in order to assemble the machinery part of the crane and the jib. These sections are then attached to the mast. The mobile crane next adds counterweights. Crawler cranes and forklifts could be a few of the other industrial machinery that is used to erect a crane.
When the building is erected, mast extensions are added to the crane. This is how the crane's height is able to match the building's height. The crane crew utilizes what is called a top climber or a climbing frame 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 utilized to adjust the slewing unit up an extra 20 feet or 6.1m. Then, the crane driver uses the crane to insert and bolt into position one more mast section piece.