The tower crane's base is generally bolted to a big concrete pad that provides very crucial support. The base is connected to a tower or a mast and stabilizes the crane that is affixed to the inside of the structure of the building. Normally, this attachment point is to an elevator shaft or to a concrete lift.
The mast of the crane is normally 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 motor and a gear that enable 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 pounds with counter weights of 20 tons. Moreover, two limit switches are utilized in order to ensure the operator does not overload the crane. There is also another safety feature called a load moment switch to ensure that the driver does not exceed the ton meter load rating. Finally, 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 because of their extreme heights. First, the stationary structure has to be brought to the construction site by utilizing a large tractor-trailer rig setup. Then, a mobile crane is utilized so as to assemble the machine portion of the jib and the crane. These parts are then connected to the mast. The mobile crane then adds counterweights. Crawler cranes and forklifts can be some of the other industrial machines which 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 can match the building's height. The crane crew uses what is called 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 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 extra 6.1m or 20 feet. After that, the crane operator utilizes the crane to insert and bolt into position one more mast section piece.